john@basho.uucp (John Lacey) (08/10/90)
Normally, of course, one wants a scanner (and a parser) to work from
a file, perhaps stdin. Sigh. Well, I want one that works from a string.
I am using Flex 2.3, and Bison 1.11. I tried the following few #define's:
#undef YY_INPUT
#define YY_INPUT(buf,result,max_size) \
{ \
for ( result = 0; *ch_this && result < max_size; result ++ ) \
buf[result] = *ch_this++; \
}
#define YY_USER_INIT \
if ( scan_init ) { \
if ( yy_flex_debug ) \
printf ( "-- initializing for scan %d\n", scan_init ); \
ch_this = inbuffer; \
scan_init = 0; }
with the following couple of definitions and declarations in the scanner:
static char * ch_this;
extern char * inbuffer;
extern int scan_init;
and with inbuffer and scan_init defined in the code that calls yyparse().
This didn't work. Well, actually, it works the first time yyparse() is
called, but not again. Now, YY_USER_INIT is used inside an if statement
that checks yy_init, so I moved it out of there in the scanner skeleton
so that YY_USER_INIT is seen every time the scanner is called. Still
no go.
Has anyone done this, or see a way to do it, or know a way to do it, or ....
Thanks.
--
John Lacey,
E-mail: ...!osu-cis!n8emr!uncle!basho!john (coming soon: john@basho.uucp)
V-mail: (614) 436--3773, or 487--8570
"What was the name of the dog on Rin-tin-tin?" --Mickey Rivers, ex-Yankee CFptb@ittc.wec.com (Pat Broderick) (08/10/90)
In article <1990Aug10.012927.5558@basho.uucp>, john@basho.uucp (John Lacey) writes: > Normally, of course, one wants a scanner (and a parser) to work from > a file, perhaps stdin. Sigh. Well, I want one that works from a string. > ... Recently I had occasion to do something similar. What we did was roughly as follows: - strings to be parsed are maintained in memory - to parse a string a global pointer known to lex is set to point at the beginning of the string - the input() macro was redefined in terms of this pointer (standard uses getc(yyin)) The things needed might look something like: LEX: # define input() (((yytchar=yysptr>yysbuf?U(*--yysptr):getc(yyin))==10?(yylineno++,yytchar):yytchar)==EOF?0:yytchar) /* standard defn from lex */ # define input() (((yytchar=yysptr>yysbuf?U(*--yysptr):(*yynyy++))==10?(yylineno++,yytchar):yytchar)==EOF?0:yytchar) ^^^^^^^^^^ /* modified defn to use string */ extern char *yynyy; /* will pt to start of string */ Function invoking parser: char *yynyy; /* globally visible */ .... yynyy = start_of_string; yyparse(); This works fine for us, hope it helps. -- Patrick T. Broderick |ptb@ittc.wec.com | |uunet!ittc!ptb | |(412)733-6265 |
bogatko@lzga.ATT.COM (George Bogatko) (08/10/90)
In article <1990Aug10.012927.5558@basho.uucp>, john@basho.uucp (John Lacey) writes: > Has anyone done this, or see a way to do it, or know a way to do it, or .... Put these lines in your lex file after the #include lines %{ #include <stdio.h> #include <y.tab.h> extern char *mis_ptr; #undef input #undef unput # define input() (*mis_ptr=='\n'?0:*mis_ptr++) # define unput(c) (*--mis_ptr=(c) ) %} Now have a char buff called myinputstring char myinputstring[100]; do the following in main: char *mis_ptr; main() { for(;;) { gets(buf); mis_ptr = buf; yylex(); } } I think you get the picture now? GB
jal@valha1.ATT.COM (Joseph A. Leggio) (08/12/90)
From article <1990Aug10.012927.5558@basho.uucp>, by john@basho.uucp (John Lacey): > Normally, of course, one wants a scanner (and a parser) to work from > a file, perhaps stdin. Sigh. Well, I want one that works from a string. > > Has anyone done this, or see a way to do it, or know a way to do it, or .... > > -- > John Lacey, I have used these "input" and "unput" routines in many programs where I wanted complete control of the input stream. The example here uses fgets to fill a character array from stdin, but you could fill it from any source you wish. You only need point pointer "p" to the start of the array each time you read a new line. Only restriction: unput cannot back up past the start of a line. (I have not found this to be a problem as I do not usually try to match patterns which span multiple lines.) I use System V Release 3 AT&T lex, "flex" might work the same, look for the #defines for "input" and "unput" in your code. ================================================== %% Lex reg-expr's go here %% #define BUFFER_SIZE 1024 char *p; char buf[BUFFER_SIZE]; main(){ p = buf; /* point "p" to start of buf for first line */ while( fgets(buf, sizeof(buf), stdin) != NULL ) { /* read line */ yylex(); /* parse line */ p = buf; /* point "p" back to start of buf for next line */ } exit(0); } #ifdef input #undef input #endif #ifdef unput #undef unput #endif /* replacement "input" routine for lex, uses char array "buf" */ char input() { if ( p < buf + ( BUFFER_SIZE - 1 ) ) return(*p++); else return((char)0); } /* replacement "unput" routine for lex, uses char array "buf" */ unput(c) char c; { if ( p > buf ) *(--p) = c; } ============================================================= Joe Leggio WB2HOL AT&T Customer Software Services Valhalla, NY att!valha1!jal