rsalz@uunet.uu.net (Rich Salz) (06/06/90)
Submitted-by: "Arnold D. Robbins" <arnold@unix.cc.emory.edu>
Posting-number: Volume 22, Issue 89
Archive-name: gawk2.11/part03
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# Contents: ./gawk.texinfo.04 ./missing.d/strtod.c
# Wrapped by rsalz@litchi.bbn.com on Wed Jun 6 12:24:47 1990
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Xoften necessary to insure that it happens where you want it to by
Xenclosing the items to be concatenated in parentheses. For example, the
Xfollowing code fragment does not concatenate @code{file} and @code{name}
Xas you might expect:
X
X@example
Xfile = "file"
Xname = "name"
Xprint "something meaningful" > file name
X@end example
X
X@noindent
XIt is necessary to use the following:
X
X@example
Xprint "something meaningful" > (file name)
X@end example
X
XWe recommend you use parentheses around concatenation in all but the
Xmost common contexts (such as in the right-hand operand of @samp{=}).
X
X@ignore
X@code{gawk} actually now allows a concatenation on the right hand
Xside of a @code{>} redirection, but other @code{awk}s don't. So for
Xnow we won't mention that fact.
X@end ignore
X
X@node Comparison Ops, Boolean Ops, Concatenation, Expressions
X@section Comparison Expressions
X@cindex comparison expressions
X@cindex expressions, comparison
X@cindex relational operators
X@cindex operators, relational
X@cindex regexp operators
X
X@dfn{Comparison expressions} compare strings or numbers for
Xrelationships such as equality. They are written using @dfn{relational
Xoperators}, which are a superset of those in C. Here is a table of
Xthem:
X
X@table @code
X@item @var{x} < @var{y}
XTrue if @var{x} is less than @var{y}.
X
X@item @var{x} <= @var{y}
XTrue if @var{x} is less than or equal to @var{y}.
X
X@item @var{x} > @var{y}
XTrue if @var{x} is greater than @var{y}.
X
X@item @var{x} >= @var{y}
XTrue if @var{x} is greater than or equal to @var{y}.
X
X@item @var{x} == @var{y}
XTrue if @var{x} is equal to @var{y}.
X
X@item @var{x} != @var{y}
XTrue if @var{x} is not equal to @var{y}.
X
X@item @var{x} ~ @var{y}
XTrue if the string @var{x} matches the regexp denoted by @var{y}.
X
X@item @var{x} !~ @var{y}
XTrue if the string @var{x} does not match the regexp denoted by @var{y}.
X
X@item @var{subscript} in @var{array}
XTrue if array @var{array} has an element with the subscript @var{subscript}.
X@end table
X
XComparison expressions have the value 1 if true and 0 if false.
X
XThe operands of a relational operator are compared as numbers if they
Xare both numbers. Otherwise they are converted to, and compared as,
Xstrings (@pxref{Conversion}). Strings are compared by comparing the
Xfirst character of each, then the second character of each, and so on.
XThus, @code{"10"} is less than @code{"9"}.
X
XFor example,
X
X@example
X$1 == "foo"
X@end example
X
X@noindent
Xhas the value of 1, or is true, if the first field of the current input
Xrecord is precisely @samp{foo}. By contrast,
X
X@example
X$1 ~ /foo/
X@end example
X
X@noindent
Xhas the value 1 if the first field contains @samp{foo}.
X
XThe right hand operand of the @samp{~} and @samp{!~} operators may be
Xeither a constant regexp (@code{/@dots{}/}), or it may be an ordinary
Xexpression, in which case the value of the expression as a string is a
Xdynamic regexp (@pxref{Regexp Usage}).
X
X@cindex regexp as expression
XIn very recent implementations of @code{awk}, a constant regular
Xexpression in slashes by itself is also an expression. The regexp
X@code{/@var{regexp}/} is an abbreviation for this comparison expression:
X
X@example
X$0 ~ /@var{regexp}/
X@end example
X
XIn some contexts it may be necessary to write parentheses around the
Xregexp to avoid confusing the @code{gawk} parser. For example,
X@code{(/x/ - /y/) > threshold} is not allowed, but @code{((/x/) - (/y/))
X> threshold} parses properly.
X
XOne special place where @code{/foo/} is @emph{not} an abbreviation for
X@code{$0 ~ /foo/} is when it is the right-hand operand of @samp{~} or
X@samp{!~}!
X
X@node Boolean Ops, Assignment Ops, Comparison Ops, Expressions
X@section Boolean Expressions
X@cindex expressions, boolean
X@cindex boolean expressions
X@cindex operators, boolean
X@cindex boolean operators
X@cindex logical operations
X@cindex and operator
X@cindex or operator
X@cindex not operator
X
XA @dfn{boolean expression} is combination of comparison expressions or
Xmatching expressions, using the @dfn{boolean operators} ``or''
X(@samp{||}), ``and'' (@samp{&&}), and ``not'' (@samp{!}), along with
Xparentheses to control nesting. The truth of the boolean expression is
Xcomputed by combining the truth values of the component expressions.
X
XBoolean expressions can be used wherever comparison and matching
Xexpressions can be used. They can be used in @code{if} and @code{while}
Xstatements. They have numeric values (1 if true, 0 if false), which
Xcome into place if the result of the boolean expression is stored in a
Xvariable, or used in arithmetic.
X
XIn addition, every boolean expression is also a valid boolean pattern, so
Xyou can use it as a pattern to control the execution of rules.
X
XHere are descriptions of the three boolean operators, with an example of
Xeach. It may be instructive to compare these examples with the
Xanalogous examples of boolean patterns (@pxref{Boolean Patterns}), which
Xuse the same boolean operators in patterns instead of expressions.
X
X@table @code
X@item @var{boolean1} && @var{boolean2}
XTrue if both @var{boolean1} and @var{boolean2} are true. For example,
Xthe following statement prints the current input record if it contains
Xboth @samp{2400} and @samp{foo}.@refill
X
X@example
Xif ($0 ~ /2400/ && $0 ~ /foo/) print
X@end example
X
XThe subexpression @var{boolean2} is evaluated only if @var{boolean1}
Xis true. This can make a difference when @var{boolean2} contains
Xexpressions that have side effects: in the case of @code{$0 ~ /foo/ &&
X($2 == bar++)}, the variable @code{bar} is not incremented if there is
Xno @samp{foo} in the record.
X
X@item @var{boolean1} || @var{boolean2}
XTrue if at least one of @var{boolean1} and @var{boolean2} is true.
XFor example, the following command prints all records in the input
Xfile @file{BBS-list} that contain @emph{either} @samp{2400} or
X@samp{foo}, or both.@refill
X
X@example
Xawk '@{ if ($0 ~ /2400/ || $0 ~ /foo/) print @}' BBS-list
X@end example
X
XThe subexpression @var{boolean2} is evaluated only if @var{boolean1}
Xis false. This can make a difference when @var{boolean2} contains
Xexpressions that have side effects.
X
X@item !@var{boolean}
XTrue if @var{boolean} is false. For example, the following program prints
Xall records in the input file @file{BBS-list} that do @emph{not} contain the
Xstring @samp{foo}.
X
X@example
Xawk '@{ if (! ($0 ~ /foo/)) print @}' BBS-list
X@end example
X@end table
X
X@node Assignment Ops, Increment Ops, Boolean Ops, Expressions
X@section Assignment Expressions
X@cindex assignment operators
X@cindex operators, assignment
X@cindex expressions, assignment
X
XAn @dfn{assignment} is an expression that stores a new value into a
Xvariable. For example, let's assign the value 1 to the variable
X@code{z}:@refill
X
X@example
Xz = 1
X@end example
X
XAfter this expression is executed, the variable @code{z} has the value 1.
XWhatever old value @code{z} had before the assignment is forgotten.
X
XAssignments can store string values also. For example, this would store
Xthe value @code{"this food is good"} in the variable @code{message}:
X
X@example
Xthing = "food"
Xpredicate = "good"
Xmessage = "this " thing " is " predicate
X@end example
X
X@noindent
X(This also illustrates concatenation of strings.)
X
XThe @samp{=} sign is called an @dfn{assignment operator}. It is the
Xsimplest assignment operator because the value of the right-hand
Xoperand is stored unchanged.
X
X@cindex side effect
XMost operators (addition, concatenation, and so on) have no effect
Xexcept to compute a value. If you ignore the value, you might as well
Xnot use the operator. An assignment operator is different; it does
Xproduce a value, but even if you ignore the value, the assignment still
Xmakes itself felt through the alteration of the variable. We call this
Xa @dfn{side effect}.
X
X@cindex lvalue
XThe left-hand operand of an assignment need not be a variable
X(@pxref{Variables}); it can also be a field (@pxref{Changing Fields}) or
Xan array element (@pxref{Arrays}). These are all called @dfn{lvalues},
Xwhich means they can appear on the left-hand side of an assignment operator.
XThe right-hand operand may be any expression; it produces the new value
Xwhich the assignment stores in the specified variable, field or array
Xelement.
X
XIt is important to note that variables do @emph{not} have permanent types.
XThe type of a variable is simply the type of whatever value it happens
Xto hold at the moment. In the following program fragment, the variable
X@code{foo} has a numeric value at first, and a string value later on:
X
X@example
Xfoo = 1
Xprint foo
Xfoo = "bar"
Xprint foo
X@end example
X
X@noindent
XWhen the second assignment gives @code{foo} a string value, the fact that
Xit previously had a numeric value is forgotten.
X
XAn assignment is an expression, so it has a value: the same value that
Xis assigned. Thus, @code{z = 1} as an expression has the value 1.
XOne consequence of this is that you can write multiple assignments together:
X
X@example
Xx = y = z = 0
X@end example
X
X@noindent
Xstores the value 0 in all three variables. It does this because the
Xvalue of @code{z = 0}, which is 0, is stored into @code{y}, and then
Xthe value of @code{y = z = 0}, which is 0, is stored into @code{x}.
X
XYou can use an assignment anywhere an expression is called for. For
Xexample, it is valid to write @code{x != (y = 1)} to set @code{y} to 1
Xand then test whether @code{x} equals 1. But this style tends to make
Xprograms hard to read; except in a one-shot program, you should
Xrewrite it to get rid of such nesting of assignments. This is never very
Xhard.
X
XAside from @samp{=}, there are several other assignment operators that
Xdo arithmetic with the old value of the variable. For example, the
Xoperator @samp{+=} computes a new value by adding the right-hand value
Xto the old value of the variable. Thus, the following assignment adds
X5 to the value of @code{foo}:
X
X@example
Xfoo += 5
X@end example
X
X@noindent
XThis is precisely equivalent to the following:
X
X@example
Xfoo = foo + 5
X@end example
X
X@noindent
XUse whichever one makes the meaning of your program clearer.
X
XHere is a table of the arithmetic assignment operators. In each
Xcase, the right-hand operand is an expression whose value is converted
Xto a number.
X
X@table @code
X@item @var{lvalue} += @var{increment}
XAdds @var{increment} to the value of @var{lvalue} to make the new value
Xof @var{lvalue}.
X
X@item @var{lvalue} -= @var{decrement}
XSubtracts @var{decrement} from the value of @var{lvalue}.
X
X@item @var{lvalue} *= @var{coefficient}
XMultiplies the value of @var{lvalue} by @var{coefficient}.
X
X@item @var{lvalue} /= @var{quotient}
XDivides the value of @var{lvalue} by @var{quotient}.
X
X@item @var{lvalue} %= @var{modulus}
XSets @var{lvalue} to its remainder by @var{modulus}.
X
X@item @var{lvalue} ^= @var{power}
X@itemx @var{lvalue} **= @var{power}
XRaises @var{lvalue} to the power @var{power}.
X@end table
X
X@node Increment Ops, Conversion, Assignment Ops, Expressions
X@section Increment Operators
X
X@cindex increment operators
X@cindex operators, increment
X@dfn{Increment operators} increase or decrease the value of a variable
Xby 1. You could do the same thing with an assignment operator, so
Xthe increment operators add no power to the @code{awk} language; but they
Xare convenient abbreviations for something very common.
X
XThe operator to add 1 is written @samp{++}. It can be used to increment
Xa variable either before or after taking its value.
X
XTo pre-increment a variable @var{v}, write @code{++@var{v}}. This adds
X1 to the value of @var{v} and that new value is also the value of this
Xexpression. The assignment expression @code{@var{v} += 1} is completely
Xequivalent.
X
XWriting the @samp{++} after the variable specifies post-increment. This
Xincrements the variable value just the same; the difference is that the
Xvalue of the increment expression itself is the variable's @emph{old}
Xvalue. Thus, if @code{foo} has value 4, then the expression @code{foo++}
Xhas the value 4, but it changes the value of @code{foo} to 5.
X
XThe post-increment @code{foo++} is nearly equivalent to writing @code{(foo
X+= 1) - 1}. It is not perfectly equivalent because all numbers in
X@code{awk} are floating point: in floating point, @code{foo + 1 - 1} does
Xnot necessarily equal @code{foo}. But the difference is minute as
Xlong as you stick to numbers that are fairly small (less than a trillion).
X
XAny lvalue can be incremented. Fields and array elements are incremented
Xjust like variables.
X
XThe decrement operator @samp{--} works just like @samp{++} except that
Xit subtracts 1 instead of adding. Like @samp{++}, it can be used before
Xthe lvalue to pre-decrement or after it to post-decrement.
X
XHere is a summary of increment and decrement expressions.
X
X@table @code
X@item ++@var{lvalue}
XThis expression increments @var{lvalue} and the new value becomes the
Xvalue of this expression.
X
X@item @var{lvalue}++
XThis expression causes the contents of @var{lvalue} to be incremented.
XThe value of the expression is the @emph{old} value of @var{lvalue}.
X
X@item --@var{lvalue}
XLike @code{++@var{lvalue}}, but instead of adding, it subtracts. It
Xdecrements @var{lvalue} and delivers the value that results.
X
X@item @var{lvalue}--
XLike @code{@var{lvalue}++}, but instead of adding, it subtracts. It
Xdecrements @var{lvalue}. The value of the expression is the @emph{old}
Xvalue of @var{lvalue}.
X@end table
X
X@node Conversion, Conditional Exp, Increment Ops, Expressions
X@section Conversion of Strings and Numbers
X
X@cindex conversion of strings and numbers
XStrings are converted to numbers, and numbers to strings, if the context
Xof the @code{awk} program demands it. For example, if the value of
Xeither @code{foo} or @code{bar} in the expression @code{foo + bar}
Xhappens to be a string, it is converted to a number before the addition
Xis performed. If numeric values appear in string concatenation, they
Xare converted to strings. Consider this:@refill
X
X@example
Xtwo = 2; three = 3
Xprint (two three) + 4
X@end example
X
X@noindent
XThis eventually prints the (numeric) value 27. The numeric values of
Xthe variables @code{two} and @code{three} are converted to strings and
Xconcatenated together, and the resulting string is converted back to the
Xnumber 23, to which 4 is then added.
X
XIf, for some reason, you need to force a number to be converted to a
Xstring, concatenate the null string with that number. To force a string
Xto be converted to a number, add zero to that string.
X
XStrings are converted to numbers by interpreting them as numerals:
X@code{"2.5"} converts to 2.5, and @code{"1e3"} converts to 1000.
XStrings that can't be interpreted as valid numbers are converted to
Xzero.
X
X@vindex OFMT
XThe exact manner in which numbers are converted into strings is controlled
Xby the @code{awk} built-in variable @code{OFMT} (@pxref{Built-in Variables}).
XNumbers are converted using a special
Xversion of the @code{sprintf} function (@pxref{Built-in}) with @code{OFMT}
Xas the format specifier.@refill
X
X@code{OFMT}'s default value is @code{"%.6g"}, which prints a value with
Xat least six significant digits. For some applications you will want to
Xchange it to specify more precision. Double precision on most modern
Xmachines gives you 16 or 17 decimal digits of precision.
X
XStrange results can happen if you set @code{OFMT} to a string that doesn't
Xtell @code{sprintf} how to format floating point numbers in a useful way.
XFor example, if you forget the @samp{%} in the format, all numbers will be
Xconverted to the same constant string.@refill
X
X@node Conditional Exp, Function Calls, Conversion, Expressions
X@section Conditional Expressions
X@cindex conditional expression
X@cindex expression, conditional
X
XA @dfn{conditional expression} is a special kind of expression with
Xthree operands. It allows you to use one expression's value to select
Xone of two other expressions.
X
XThe conditional expression looks the same as in the C language:
X
X@example
X@var{selector} ? @var{if-true-exp} : @var{if-false-exp}
X@end example
X
X@noindent
XThere are three subexpressions. The first, @var{selector}, is always
Xcomputed first. If it is ``true'' (not zero) then @var{if-true-exp} is
Xcomputed next and its value becomes the value of the whole expression.
XOtherwise, @var{if-false-exp} is computed next and its value becomes the
Xvalue of the whole expression.
X
XFor example, this expression produces the absolute value of @code{x}:
X
X@example
Xx > 0 ? x : -x
X@end example
X
XEach time the conditional expression is computed, exactly one of
X@var{if-true-exp} and @var{if-false-exp} is computed; the other is ignored.
XThis is important when the expressions contain side effects. For example,
Xthis conditional expression examines element @code{i} of either array
X@code{a} or array @code{b}, and increments @code{i}.
X
X@example
Xx == y ? a[i++] : b[i++]
X@end example
X
X@noindent
XThis is guaranteed to increment @code{i} exactly once, because each time
Xone or the other of the two increment expressions is executed,
Xand the other is not.
X
X@node Function Calls, Precedence, Conditional Exp, Expressions
X@section Function Calls
X@cindex function call
X@cindex calling a function
X
XA @dfn{function} is a name for a particular calculation. Because it has
Xa name, you can ask for it by name at any point in the program. For
Xexample, the function @code{sqrt} computes the square root of a number.
X
XA fixed set of functions are @dfn{built in}, which means they are
Xavailable in every @code{awk} program. The @code{sqrt} function is one
Xof these. @xref{Built-in}, for a list of built-in functions and their
Xdescriptions. In addition, you can define your own functions in the
Xprogram for use elsewhere in the same program. @xref{User-defined},
Xfor how to do this.
X
X@cindex arguments in function call
XThe way to use a function is with a @dfn{function call} expression,
Xwhich consists of the function name followed by a list of
X@dfn{arguments} in parentheses. The arguments are expressions which
Xgive the raw materials for the calculation that the function will do.
XWhen there is more than one argument, they are separated by commas. If
Xthere are no arguments, write just @samp{()} after the function name.
XHere are some examples:
X
X@example
Xsqrt(x**2 + y**2) # @r{One argument}
Xatan2(y, x) # @r{Two arguments}
Xrand() # @r{No arguments}
X@end example
X
X@strong{Do not put any space between the function name and the
Xopen-parenthesis!} A user-defined function name looks just like the name of
Xa variable, and space would make the expression look like concatenation
Xof a variable with an expression inside parentheses. Space before the
Xparenthesis is harmless with built-in functions, but it is best not to get
Xinto the habit of using space, lest you do likewise for a user-defined
Xfunction one day by mistake.
X
XEach function expects a particular number of arguments. For example, the
X@code{sqrt} function must be called with a single argument, the number
Xto take the square root of:
X
X@example
Xsqrt(@var{argument})
X@end example
X
XSome of the built-in functions allow you to omit the final argument.
XIf you do so, they use a reasonable default. @xref{Built-in},
Xfor full details. If arguments are omitted in calls to user-defined
Xfunctions, then those arguments are treated as local variables,
Xinitialized to the null string (@pxref{User-defined}).
X
XLike every other expression, the function call has a value, which is
Xcomputed by the function based on the arguments you give it. In this
Xexample, the value of @code{sqrt(@var{argument})} is the square root of the
Xargument. A function can also have side effects, such as assigning the
Xvalues of certain variables or doing I/O.
X
XHere is a command to read numbers, one number per line, and print the
Xsquare root of each one:
X
X@example
Xawk '@{ print "The square root of", $1, "is", sqrt($1) @}'
X@end example
X
X@node Precedence,, Function Calls, Expressions
X@section Operator Precedence: How Operators Nest
X@cindex precedence
X@cindex operator precedence
X
X@dfn{Operator precedence} determines how operators are grouped, when
Xdifferent operators appear close by in one expression. For example,
X@samp{*} has higher precedence than @samp{+}; thus, @code{a + b * c}
Xmeans to multiply @code{b} and @code{c}, and then add @code{a} to the
Xproduct.
X
XYou can overrule the precedence of the operators by writing parentheses
Xyourself. You can think of the precedence rules as saying where the
Xparentheses are assumed if you do not write parentheses yourself. In
Xfact, it is wise always to use parentheses whenever you have an unusual
Xcombination of operators, because other people who read the program may
Xnot remember what the precedence is in this case. You might forget,
Xtoo; then you could make a mistake. Explicit parentheses will prevent
Xany such mistake.
X
XWhen operators of equal precedence are used together, the leftmost
Xoperator groups first, except for the assignment, conditional and
Xand exponentiation operators, which group in the opposite order.
XThus, @code{a - b + c} groups as @code{(a - b) + c};
X@code{a = b = c} groups as @code{a = (b = c)}.
X
XThe precedence of prefix unary operators does not matter as long as only
Xunary operators are involved, because there is only one way to parse
Xthem---innermost first. Thus, @code{$++i} means @code{$(++i)} and
X@code{++$x} means @code{++($x)}. However, when another operator follows
Xthe operand, then the precedence of the unary operators can matter.
XThus, @code{$x**2} means @code{($x)**2}, but @code{-x**2} means
X@code{-(x**2)}, because @samp{-} has lower precedence than @samp{**}
Xwhile @samp{$} has higher precedence.
X
XHere is a table of the operators of @code{awk}, in order of increasing
Xprecedence:
X
X@table @asis
X@item assignment
X@samp{=}, @samp{+=}, @samp{-=}, @samp{*=}, @samp{/=}, @samp{%=},
X@samp{^=}, @samp{**=}. These operators group right-to-left.
X
X@item conditional
X@samp{?:}. These operators group right-to-left.
X
X@item logical ``or''.
X@samp{||}.
X
X@item logical ``and''.
X@samp{&&}.
X
X@item array membership
X@code{in}.
X
X@item matching
X@samp{~}, @samp{!~}.
X
X@item relational, and redirection
XThe relational operators and the redirections have the same precedence
Xlevel. Characters such as @samp{>} serve both as relationals and as
Xredirections; the context distinguishes between the two meanings.
X
XThe relational operators are @samp{<}, @samp{<=}, @samp{==}, @samp{!=},
X@samp{>=} and @samp{>}.
X
XThe I/O redirection operators are @samp{<}, @samp{>}, @samp{>>} and
X@samp{|}.
X
XNote that I/O redirection operators in @code{print} and @code{printf}
Xstatements belong to the statement level, not to expressions. The
Xredirection does not produce an expression which could be the operand of
Xanother operator. As a result, it does not make sense to use a
Xredirection operator near another operator of lower precedence, without
Xparentheses. Such combinations, for example @samp{print foo > a ? b :
Xc}, result in syntax errors.
X
X@item concatentation
XNo special token is used to indicate concatenation.
XThe operands are simply written side by side.
X@c This is supposedly being fixed
X@ignore
XConcatenation has the same precedence as relational and redirection
Xoperators. These operators nest left to right. Thus, @code{4 5 > 6}
Xconcatenates first, yielding 1, while @code{6 < 4 5} compares first, and
Xyields @code{"05"}.
X@end ignore
X
X@item add, subtract
X@samp{+}, @samp{-}.
X
X@item multiply, divide, mod
X@samp{*}, @samp{/}, @samp{%}.
X
X@item unary plus, minus, ``not''
X@samp{+}, @samp{-}, @samp{!}.
X
X@item exponentiation
X@samp{^}, @samp{**}. These operators group right-to-left.
X
X@item increment, decrement
X@samp{++}, @samp{--}.
X
X@item field
X@samp{$}.
X@end table
X
X@node Statements, Arrays, Expressions, Top
X@chapter Actions: Control Statements
X@cindex control statement
X
X@dfn{Control statements} such as @code{if}, @code{while}, and so on
Xcontrol the flow of execution in @code{awk} programs. Most of the
Xcontrol statements in @code{awk} are patterned on similar statements in
XC.
X
XAll the control statements start with special keywords such as @code{if}
Xand @code{while}, to distinguish them from simple expressions.
X
XMany control statements contain other statements; for example, the
X@code{if} statement contains another statement which may or may not be
Xexecuted. The contained statement is called the @dfn{body}. If you
Xwant to include more than one statement in the body, group them into a
Xsingle compound statement with curly braces, separating them with
Xnewlines or semicolons.
X
X@menu
X* If Statement:: Conditionally execute some @code{awk} statements.
X
X* While Statement:: Loop until some condition is satisfied.
X
X* Do Statement:: Do specified action while looping until some
X condition is satisfied.
X
X* For Statement:: Another looping statement, that provides
X initialization and increment clauses.
X
X* Break Statement:: Immediately exit the innermost enclosing loop.
X
X* Continue Statement:: Skip to the end of the innermost enclosing loop.
X
X* Next Statement:: Stop processing the current input record.
X
X* Exit Statement:: Stop execution of @code{awk}.
X@end menu
X
X@node If Statement, While Statement, Statements, Statements
X@section The @code{if} Statement
X
X@cindex @code{if} statement
XThe @code{if}-@code{else} statement is @code{awk}'s decision-making
Xstatement. It looks like this:@refill
X
X@example
Xif (@var{condition}) @var{then-body} @r{[}else @var{else-body}@r{]}
X@end example
X
X@noindent
XHere @var{condition} is an expression that controls what the rest of the
Xstatement will do. If @var{condition} is true, @var{then-body} is
Xexecuted; otherwise, @var{else-body} is executed (assuming that the
X@code{else} clause is present). The @code{else} part of the statement is
Xoptional. The condition is considered false if its value is zero or
Xthe null string, true otherwise.@refill
X
XHere is an example:
X
X@example
Xif (x % 2 == 0)
X print "x is even"
Xelse
X print "x is odd"
X@end example
X
XIn this example, if the expression @code{x % 2 == 0} is true (that is,
Xthe value of @code{x} is divisible by 2), then the first @code{print}
Xstatement is executed, otherwise the second @code{print} statement is
Xperformed.@refill
X
XIf the @code{else} appears on the same line as @var{then-body}, and
X@var{then-body} is not a compound statement (i.e., not surrounded by
Xcurly braces), then a semicolon must separate @var{then-body} from
X@code{else}. To illustrate this, let's rewrite the previous example:
X
X@group
X@example
Xawk '@{ if (x % 2 == 0) print "x is even"; else
X print "x is odd" @}'
X@end example
X@end group
X
X@noindent
XIf you forget the @samp{;}, @code{awk} won't be able to parse the
Xstatement, and you will get a syntax error.
X
XWe would not actually write this example this way, because a human
Xreader might fail to see the @code{else} if it were not the first thing
Xon its line.
X
X@node While Statement, Do Statement, If Statement, Statements
X@section The @code{while} Statement
X@cindex @code{while} statement
X@cindex loop
X@cindex body of a loop
X
XIn programming, a @dfn{loop} means a part of a program that is (or at least can
Xbe) executed two or more times in succession.
X
XThe @code{while} statement is the simplest looping statement in
X@code{awk}. It repeatedly executes a statement as long as a condition is
Xtrue. It looks like this:
X
X@example
Xwhile (@var{condition})
X @var{body}
X@end example
X
X@noindent
XHere @var{body} is a statement that we call the @dfn{body} of the loop,
Xand @var{condition} is an expression that controls how long the loop
Xkeeps running.
X
XThe first thing the @code{while} statement does is test @var{condition}.
XIf @var{condition} is true, it executes the statement @var{body}.
X(Truth, as usual in @code{awk}, means that the value of @var{condition}
Xis not zero and not a null string.) After @var{body} has been executed,
X@var{condition} is tested again, and if it is still true, @var{body} is
Xexecuted again. This process repeats until @var{condition} is no longer
Xtrue. If @var{condition} is initially false, the body of the loop is
Xnever executed.@refill
X
XThis example prints the first three fields of each record, one per line.
X
X@example
Xawk '@{ i = 1
X while (i <= 3) @{
X print $i
X i++
X @}
X@}'
X@end example
X
X@noindent
XHere the body of the loop is a compound statement enclosed in braces,
Xcontaining two statements.
X
XThe loop works like this: first, the value of @code{i} is set to 1.
XThen, the @code{while} tests whether @code{i} is less than or equal to
Xthree. This is the case when @code{i} equals one, so the @code{i}-th
Xfield is printed. Then the @code{i++} increments the value of @code{i}
Xand the loop repeats. The loop terminates when @code{i} reaches 4.
X
XAs you can see, a newline is not required between the condition and the
Xbody; but using one makes the program clearer unless the body is a
Xcompound statement or is very simple. The newline after the open-brace
Xthat begins the compound statement is not required either, but the
Xprogram would be hard to read without it.
X
X@node Do Statement, For Statement, While Statement, Statements
X@section The @code{do}-@code{while} Statement
X
XThe @code{do} loop is a variation of the @code{while} looping statement.
XThe @code{do} loop executes the @var{body} once, then repeats @var{body}
Xas long as @var{condition} is true. It looks like this:
X
X@group
X@example
Xdo
X @var{body}
Xwhile (@var{condition})
X@end example
X@end group
X
XEven if @var{condition} is false at the start, @var{body} is executed at
Xleast once (and only once, unless executing @var{body} makes
X@var{condition} true). Contrast this with the corresponding
X@code{while} statement:
X
X@example
Xwhile (@var{condition})
X @var{body}
X@end example
X
X@noindent
XThis statement does not execute @var{body} even once if @var{condition}
Xis false to begin with.
X
XHere is an example of a @code{do} statement:
X
X@example
Xawk '@{ i = 1
X do @{
X print $0
X i++
X @} while (i <= 10)
X@}'
X@end example
X
X@noindent
Xprints each input record ten times. It isn't a very realistic example,
Xsince in this case an ordinary @code{while} would do just as well. But
Xthis reflects actual experience; there is only occasionally a real use
Xfor a @code{do} statement.@refill
X
X@node For Statement, Break Statement, Do Statement, Statements
X@section The @code{for} Statement
X@cindex @code{for} statement
X
XThe @code{for} statement makes it more convenient to count iterations of a
Xloop. The general form of the @code{for} statement looks like this:@refill
X
X@example
Xfor (@var{initialization}; @var{condition}; @var{increment})
X @var{body}
X@end example
X
X@noindent
XThis statement starts by executing @var{initialization}. Then, as long
Xas @var{condition} is true, it repeatedly executes @var{body} and then
X@var{increment}. Typically @var{initialization} sets a variable to
Xeither zero or one, @var{increment} adds 1 to it, and @var{condition}
Xcompares it against the desired number of iterations.
X
XHere is an example of a @code{for} statement:
X
X@example
Xawk '@{ for (i = 1; i <= 3; i++)
X print $i
X@}'
X@end example
X
X@noindent
XThis prints the first three fields of each input record, one field per
Xline.
X
XIn the @code{for} statement, @var{body} stands for any statement, but
X@var{initialization}, @var{condition} and @var{increment} are just
Xexpressions. You cannot set more than one variable in the
X@var{initialization} part unless you use a multiple assignment statement
Xsuch as @code{x = y = 0}, which is possible only if all the initial values
Xare equal. (But you can initialize additional variables by writing
Xtheir assignments as separate statements preceding the @code{for} loop.)
X
XThe same is true of the @var{increment} part; to increment additional
Xvariables, you must write separate statements at the end of the loop.
XThe C compound expression, using C's comma operator, would be useful in
Xthis context, but it is not supported in @code{awk}.
X
XMost often, @var{increment} is an increment expression, as in the
Xexample above. But this is not required; it can be any expression
Xwhatever. For example, this statement prints all the powers of 2
Xbetween 1 and 100:
X
X@example
Xfor (i = 1; i <= 100; i *= 2)
X print i
X@end example
X
XAny of the three expressions in the parentheses following @code{for} may
Xbe omitted if there is nothing to be done there. Thus, @w{@samp{for (;x
X> 0;)}} is equivalent to @w{@samp{while (x > 0)}}. If the
X@var{condition} is omitted, it is treated as @var{true}, effectively
Xyielding an infinite loop.@refill
X
XIn most cases, a @code{for} loop is an abbreviation for a @code{while}
Xloop, as shown here:
X
X@example
X@var{initialization}
Xwhile (@var{condition}) @{
X @var{body}
X @var{increment}
X@}
X@end example
X
X@noindent
XThe only exception is when the @code{continue} statement
X(@pxref{Continue Statement}) is used inside the loop; changing a
X@code{for} statement to a @code{while} statement in this way can change
Xthe effect of the @code{continue} statement inside the loop.
X
XThere is an alternate version of the @code{for} loop, for iterating over
Xall the indices of an array:
X
X@example
Xfor (i in array)
X @var{do something with} array[i]
X@end example
X
X@noindent
X@xref{Arrays}, for more information on this version of the @code{for} loop.
X
XThe @code{awk} language has a @code{for} statement in addition to a
X@code{while} statement because often a @code{for} loop is both less work to
Xtype and more natural to think of. Counting the number of iterations is
Xvery common in loops. It can be easier to think of this counting as part
Xof looping rather than as something to do inside the loop.
X
XThe next section has more complicated examples of @code{for} loops.
X
X@node Break Statement, Continue Statement, For Statement, Statements
X@section The @code{break} Statement
X@cindex @code{break} statement
X@cindex loops, exiting
X
XThe @code{break} statement jumps out of the innermost @code{for},
X@code{while}, or @code{do}-@code{while} loop that encloses it. The
Xfollowing example finds the smallest divisor of any integer, and also
Xidentifies prime numbers:@refill
X
X@example
Xawk '# find smallest divisor of num
X @{ num = $1
X for (div = 2; div*div <= num; div++)
X if (num % div == 0)
X break
X if (num % div == 0)
X printf "Smallest divisor of %d is %d\n", num, div
X else
X printf "%d is prime\n", num @}'
X@end example
X
XWhen the remainder is zero in the first @code{if} statement, @code{awk}
Ximmediately @dfn{breaks out} of the containing @code{for} loop. This means
Xthat @code{awk} proceeds immediately to the statement following the loop
Xand continues processing. (This is very different from the @code{exit}
Xstatement (@pxref{Exit Statement}) which stops the entire @code{awk}
Xprogram.)@refill
X
XHere is another program equivalent to the previous one. It illustrates how
Xthe @var{condition} of a @code{for} or @code{while} could just as well be
Xreplaced with a @code{break} inside an @code{if}:
X
X@example
Xawk '# find smallest divisor of num
X @{ num = $1
X for (div = 2; ; div++) @{
X if (num % div == 0) @{
X printf "Smallest divisor of %d is %d\n", num, div
X break
X @}
X if (div*div > num) @{
X printf "%d is prime\n", num
X break
X @}
X @}
X@}'
X@end example
X
X@node Continue Statement, Next Statement, Break Statement, Statements
X@section The @code{continue} Statement
X
X@cindex @code{continue} statement
XThe @code{continue} statement, like @code{break}, is used only inside
X@code{for}, @code{while}, and @code{do}-@code{while} loops. It skips
Xover the rest of the loop body, causing the next cycle around the loop
Xto begin immediately. Contrast this with @code{break}, which jumps out
Xof the loop altogether. Here is an example:@refill
X
X@example
X# print names that don't contain the string "ignore"
X
X# first, save the text of each line
X@{ names[NR] = $0 @}
X
X# print what we're interested in
XEND @{
X for (x in names) @{
X if (names[x] ~ /ignore/)
X continue
X print names[x]
X @}
X@}
X@end example
X
XIf one of the input records contains the string @samp{ignore}, this
Xexample skips the print statement for that record, and continues back to
Xthe first statement in the loop.
X
XThis isn't a practical example of @code{continue}, since it would be
Xjust as easy to write the loop like this:
X
X@example
Xfor (x in names)
X if (names[x] !~ /ignore/)
X print names[x]
X@end example
X
XThe @code{continue} statement in a @code{for} loop directs @code{awk} to
Xskip the rest of the body of the loop, and resume execution with the
Xincrement-expression of the @code{for} statement. The following program
Xillustrates this fact:@refill
X
X@example
Xawk 'BEGIN @{
X for (x = 0; x <= 20; x++) @{
X if (x == 5)
X continue
X printf ("%d ", x)
X @}
X print ""
X@}'
X@end example
X
X@noindent
XThis program prints all the numbers from 0 to 20, except for 5, for
Xwhich the @code{printf} is skipped. Since the increment @code{x++}
Xis not skipped, @code{x} does not remain stuck at 5. Contrast the
X@code{for} loop above with the @code{while} loop:
X
X@example
Xawk 'BEGIN @{
X x = 0
X while (x <= 20) @{
X if (x == 5)
X continue
X printf ("%d ", x)
X x++
X @}
X print ""
X@}'
X@end example
X
X@noindent
XThis program loops forever once @code{x} gets to 5.
X
X@node Next Statement, Exit Statement, Continue Statement, Statements
X@section The @code{next} Statement
X@cindex @code{next} statement
X
XThe @code{next} statement forces @code{awk} to immediately stop processing
Xthe current record and go on to the next record. This means that no
Xfurther rules are executed for the current record. The rest of the
Xcurrent rule's action is not executed either.
X
XContrast this with the effect of the @code{getline} function
X(@pxref{Getline}). That too causes @code{awk} to read the next record
Ximmediately, but it does not alter the flow of control in any way. So
Xthe rest of the current action executes with a new input record.
X
XAt the grossest level, @code{awk} program execution is a loop that reads
Xan input record and then tests each rule's pattern against it. If you
Xthink of this loop as a @code{for} statement whose body contains the
Xrules, then the @code{next} statement is analogous to a @code{continue}
Xstatement: it skips to the end of the body of this implicit loop, and
Xexecutes the increment (which reads another record).
X
XFor example, if your @code{awk} program works only on records with four
Xfields, and you don't want it to fail when given bad input, you might
Xuse this rule near the beginning of the program:
X
X@example
XNF != 4 @{
X printf("line %d skipped: doesn't have 4 fields", FNR) > "/dev/stderr"
X next
X@}
X@end example
X
X@noindent
Xso that the following rules will not see the bad record. The error
Xmessage is redirected to the standard error output stream, as error
Xmessages should be. @xref{Special Files}.
X
XThe @code{next} statement is not allowed in a @code{BEGIN} or @code{END}
Xrule.
X
X@node Exit Statement, , Next Statement, Statements
X@section The @code{exit} Statement
X
X@cindex @code{exit} statement
XThe @code{exit} statement causes @code{awk} to immediately stop
Xexecuting the current rule and to stop processing input; any remaining input
Xis ignored.@refill
X
XIf an @code{exit} statement is executed from a @code{BEGIN} rule the
Xprogram stops processing everything immediately. No input records are
Xread. However, if an @code{END} rule is present, it is executed
X(@pxref{BEGIN/END}).
X
XIf @code{exit} is used as part of an @code{END} rule, it causes
Xthe program to stop immediately.
X
XAn @code{exit} statement that is part an ordinary rule (that is, not part
Xof a @code{BEGIN} or @code{END} rule) stops the execution of any further
Xautomatic rules, but the @code{END} rule is executed if there is one.
XIf you don't want the @code{END} rule to do its job in this case, you
Xcan set a variable to nonzero before the @code{exit} statement, and check
Xthat variable in the @code{END} rule.
X
XIf an argument is supplied to @code{exit}, its value is used as the exit
Xstatus code for the @code{awk} process. If no argument is supplied,
X@code{exit} returns status zero (success).@refill
X
XFor example, let's say you've discovered an error condition you really
Xdon't know how to handle. Conventionally, programs report this by
Xexiting with a nonzero status. Your @code{awk} program can do this
Xusing an @code{exit} statement with a nonzero argument. Here's an
Xexample of this:@refill
X
X@example
XBEGIN @{
X if (("date" | getline date_now) < 0) @{
X print "Can't get system date" > "/dev/stderr"
X exit 4
X @}
X@}
X@end example
X
X@node Arrays, Built-in, Statements, Top
X@chapter Arrays in @code{awk}
X
XAn @dfn{array} is a table of various values, called @dfn{elements}. The
Xelements of an array are distinguished by their @dfn{indices}. Indices
Xmay be either numbers or strings. Each array has a name, which looks
Xlike a variable name, but must not be in use as a variable name in the
Xsame @code{awk} program.
X
X@menu
X* Intro: Array Intro. Basic facts about arrays in @code{awk}.
X* Reference to Elements:: How to examine one element of an array.
X* Assigning Elements:: How to change an element of an array.
X* Example: Array Example. Sample program explained.
X
X* Scanning an Array:: A variation of the @code{for} statement. It loops
X through the indices of an array's existing elements.
X
X* Delete:: The @code{delete} statement removes an element from an array.
X
X* Multi-dimensional:: Emulating multi-dimensional arrays in @code{awk}.
X* Multi-scanning:: Scanning multi-dimensional arrays.
X@end menu
X
X@node Array Intro, Reference to Elements, Arrays, Arrays
X@section Introduction to Arrays
X
X@cindex arrays
XThe @code{awk} language has one-dimensional @dfn{arrays} for storing groups
Xof related strings or numbers.
X
XEvery @code{awk} array must have a name. Array names have the same
Xsyntax as variable names; any valid variable name would also be a valid
Xarray name. But you cannot use one name in both ways (as an array and
Xas a variable) in one @code{awk} program.
X
XArrays in @code{awk} superficially resemble arrays in other programming
Xlanguages; but there are fundamental differences. In @code{awk}, you
Xdon't need to specify the size of an array before you start to use it.
XWhat's more, in @code{awk} any number or even a string may be used as an
Xarray index.
X
XIn most other languages, you have to @dfn{declare} an array and specify
Xhow many elements or components it has. In such languages, the
Xdeclaration causes a contiguous block of memory to be allocated for that
Xmany elements. An index in the array must be a positive integer; for
Xexample, the index 0 specifies the first element in the array, which is
Xactually stored at the beginning of the block of memory. Index 1
Xspecifies the second element, which is stored in memory right after the
Xfirst element, and so on. It is impossible to add more elements to the
Xarray, because it has room for only as many elements as you declared.
X
XA contiguous array of four elements might look like this, conceptually,
Xif the element values are 8, @code{"foo"}, @code{""} and 30:@refill
X
X@example
X+---------+---------+--------+---------+
X| 8 | "foo" | "" | 30 | @r{value}
X+---------+---------+--------+---------+
X 0 1 2 3 @r{index}
X@end example
X
X@noindent
XOnly the values are stored; the indices are implicit from the order of
Xthe values. 8 is the value at index 0, because 8 appears in the
Xposition with 0 elements before it.
X
X@cindex arrays, definition of
X@cindex associative arrays
XArrays in @code{awk} are different: they are @dfn{associative}. This means
Xthat each array is a collection of pairs: an index, and its corresponding
Xarray element value:
X
X@example
X@r{Element} 4 @r{Value} 30
X@r{Element} 2 @r{Value} "foo"
X@r{Element} 1 @r{Value} 8
X@r{Element} 3 @r{Value} ""
X@end example
X
X@noindent
XWe have shown the pairs in jumbled order because their order doesn't
Xmean anything.
X
XOne advantage of an associative array is that new pairs can be added
Xat any time. For example, suppose we add to that array a tenth element
Xwhose value is @w{@code{"number ten"}}. The result is this:
X
X@example
X@r{Element} 10 @r{Value} "number ten"
X@r{Element} 4 @r{Value} 30
X@r{Element} 2 @r{Value} "foo"
X@r{Element} 1 @r{Value} 8
X@r{Element} 3 @r{Value} ""
X@end example
X
X@noindent
XNow the array is @dfn{sparse} (i.e., some indices are missing): it has
Xelements 4 and 10, but doesn't have elements 5, 6, 7, 8, or 9.@refill
X
XAnother consequence of associative arrays is that the indices don't
Xhave to be positive integers. Any number, or even a string, can be
Xan index. For example, here is an array which translates words from
XEnglish into French:
X
X@example
X@r{Element} "dog" @r{Value} "chien"
X@r{Element} "cat" @r{Value} "chat"
X@r{Element} "one" @r{Value} "un"
X@r{Element} 1 @r{Value} "un"
X@end example
X
X@noindent
XHere we decided to translate the number 1 in both spelled-out and
Xnumeric form---thus illustrating that a single array can have both
Xnumbers and strings as indices.
X
XWhen @code{awk} creates an array for you, e.g., with the @code{split}
Xbuilt-in function (@pxref{String Functions}), that array's indices
Xare consecutive integers starting at 1.
X
X@node Reference to Elements, Assigning Elements, Array Intro, Arrays
X@section Referring to an Array Element
X@cindex array reference
X@cindex element of array
X@cindex reference to array
X
XThe principal way of using an array is to refer to one of its elements.
XAn array reference is an expression which looks like this:
X
X@example
X@var{array}[@var{index}]
X@end example
X
X@noindent
XHere @var{array} is the name of an array. The expression @var{index} is
Xthe index of the element of the array that you want.
X
XThe value of the array reference is the current value of that array
Xelement. For example, @code{foo[4.3]} is an expression for the element
Xof array @code{foo} at index 4.3.
X
XIf you refer to an array element that has no recorded value, the value
Xof the reference is @code{""}, the null string. This includes elements
Xto which you have not assigned any value, and elements that have been
Xdeleted (@pxref{Delete}). Such a reference automatically creates that
Xarray element, with the null string as its value. (In some cases,
Xthis is unfortunate, because it might waste memory inside @code{awk}).
X
X@cindex arrays, determining presence of elements
XYou can find out if an element exists in an array at a certain index with
Xthe expression:
X
X@example
X@var{index} in @var{array}
X@end example
X
X@noindent
XThis expression tests whether or not the particular index exists,
Xwithout the side effect of creating that element if it is not present.
XThe expression has the value 1 (true) if @code{@var{array}[@var{index}]}
Xexists, and 0 (false) if it does not exist.@refill
X
XFor example, to test whether the array @code{frequencies} contains the
Xindex @code{"2"}, you could write this statement:@refill
X
X@example
Xif ("2" in frequencies) print "Subscript \"2\" is present."
X@end example
X
XNote that this is @emph{not} a test of whether or not the array
X@code{frequencies} contains an element whose @emph{value} is @code{"2"}.
X(There is no way to do that except to scan all the elements.) Also, this
X@emph{does not} create @code{frequencies["2"]}, while the following
X(incorrect) alternative would do so:@refill
X
X@example
Xif (frequencies["2"] != "") print "Subscript \"2\" is present."
X@end example
X
X@node Assigning Elements, Array Example, Reference to Elements, Arrays
X@section Assigning Array Elements
X@cindex array assignment
X@cindex element assignment
X
XArray elements are lvalues: they can be assigned values just like
X@code{awk} variables:
X
X@example
X@var{array}[@var{subscript}] = @var{value}
X@end example
X
X@noindent
XHere @var{array} is the name of your array. The expression
X@var{subscript} is the index of the element of the array that you want
Xto assign a value. The expression @var{value} is the value you are
Xassigning to that element of the array.@refill
X
X@node Array Example, Scanning an Array, Assigning Elements, Arrays
X@section Basic Example of an Array
X
XThe following program takes a list of lines, each beginning with a line
Xnumber, and prints them out in order of line number. The line numbers are
Xnot in order, however, when they are first read: they are scrambled. This
Xprogram sorts the lines by making an array using the line numbers as
Xsubscripts. It then prints out the lines in sorted order of their numbers.
XIt is a very simple program, and gets confused if it encounters repeated
Xnumbers, gaps, or lines that don't begin with a number.@refill
X
X@example
X@{
X if ($1 > max)
X max = $1
X arr[$1] = $0
X@}
X
XEND @{
X for (x = 1; x <= max; x++)
X print arr[x]
X@}
X@end example
X
X@ignore
XThe first rule just initializes the variable @code{max}. (This is not
Xstrictly necessary, since an uninitialized variable has the null string
Xas its value, and the null string is effectively zero when used in
Xa context where a number is required.)
X@end ignore
X
XThe first rule keeps track of the largest line number seen so far;
Xit also stores each line into the array @code{arr}, at an index that
Xis the line's number.
X
XThe second rule runs after all the input has been read, to print out
Xall the lines.
X
XWhen this program is run with the following input:
X
X@example
X5 I am the Five man
X2 Who are you? The new number two!
X4 . . . And four on the floor
X1 Who is number one?
X3 I three you.
X@end example
X
X@noindent
Xits output is this:
X
X@example
X1 Who is number one?
X2 Who are you? The new number two!
X3 I three you.
X4 . . . And four on the floor
X5 I am the Five man
X@end example
X
END_OF_FILE
if test 49666 -ne `wc -c <'./gawk.texinfo.04'`; then
echo shar: \"'./gawk.texinfo.04'\" unpacked with wrong size!
fi
# end of './gawk.texinfo.04'
fi
if test -f './missing.d/strtod.c' -a "${1}" != "-c" ; then
echo shar: Will not clobber existing file \"'./missing.d/strtod.c'\"
else
echo shar: Extracting \"'./missing.d/strtod.c'\" \(2023 characters\)
sed "s/^X//" >'./missing.d/strtod.c' <<'END_OF_FILE'
X/*
X * strtod.c
X *
X * Stupid version of System V strtod(3) library routine.
X * Does no overflow/underflow checking.
X *
X * A real number is defined to be
X * optional leading white space
X * optional sign
X * string of digits with optional decimal point
X * optional 'e' or 'E'
X * followed by optional sign or space
X * followed by an integer
X *
X * if ptr is not NULL a pointer to the character terminating the
X * scan is returned in *ptr. If no number formed, *ptr is set to str
X * and 0 is returned.
X *
X * For speed, we don't do the conversion ourselves. Instead, we find
X * the end of the number and then call atof() to do the dirty work.
X * This bought us a 10% speedup on a sample program at uunet.uu.net.
X */
X
X#include <ctype.h>
X
Xextern double atof();
X
Xdouble
Xstrtod (s, ptr)
Xregister char *s, **ptr;
X{
X double ret = 0.0;
X char *start = s;
X char *begin = NULL;
X int success = 0;
X
X /* optional white space */
X while (isspace(*s))
X s++;
X
X /* optional sign */
X if (*s == '+' || *s == '-') {
X s++;
X if (*(s-1) == '-')
X begin = s - 1;
X else
X begin = s;
X }
X
X /* string of digits with optional decimal point */
X if (isdigit(*s) && ! begin)
X begin = s;
X
X while (isdigit(*s)) {
X s++;
X success++;
X }
X
X if (*s == '.') {
X if (! begin)
X begin = s;
X s++;
X while (isdigit(*s))
X s++;
X success++;
X }
X
X if (s == start || success == 0) /* nothing there */
X goto out;
X
X /*
X * optional 'e' or 'E'
X * followed by optional sign or space
X * followed by an integer
X */
X
X if (*s == 'e' || *s == 'E') {
X s++;
X
X /* XXX - atof probably doesn't allow spaces here */
X while (isspace(*s))
X s++;
X
X if (*s == '+' || *s == '-')
X s++;
X
X while (isdigit(*s))
X s++;
X }
X
X /* go for it */
X ret = atof(begin);
X
Xout:
X if (! success)
X s = start; /* in case all we did was skip whitespace */
X
X if (ptr)
X *ptr = s;
X
X return ret;
X}
X
X#ifdef TEST
Xmain (argc, argv)
Xint argc;
Xchar **argv;
X{
X double d;
X char *p;
X
X for (argc--, argv++; argc; argc--, argv++) {
X d = strtod (*argv, & p);
X printf ("%lf [%s]\n", d, p);
X }
X}
X#endif
END_OF_FILE
if test 2023 -ne `wc -c <'./missing.d/strtod.c'`; then
echo shar: \"'./missing.d/strtod.c'\" unpacked with wrong size!
fi
# end of './missing.d/strtod.c'
fi
echo shar: End of archive 3 \(of 16\).
cp /dev/null ark3isdone
MISSING=""
for I in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 ; do
if test ! -f ark${I}isdone ; then
MISSING="${MISSING} ${I}"
fi
done
if test "${MISSING}" = "" ; then
echo You have unpacked all 16 archives.
rm -f ark[1-9]isdone ark[1-9][0-9]isdone
else
echo You still must unpack the following archives:
echo " " ${MISSING}
fi
exit 0
exit 0 # Just in case...
--
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