pjh@mccc.UUCP (Peter J. Holsberg) (02/25/88)
Dumb question: if in an assignment like
x = 3;
where x is declared a double, the 3 is simply widened to the size of a
double, why does this fail?
min = minimum( min, x );
where
double minimum( double, double );
Thanks.
--
Peter Holsberg UUCP: {rutgers!}princeton!mccc!pjh
Technology Division CompuServe: 70240,334
Mercer College GEnie: PJHOLSBERG
Trenton, NJ 08690 Voice: 1-609-586-4800gwyn@brl-smoke.ARPA (Doug Gwyn ) (02/26/88)
In article <239@mccc.UUCP> pjh@mccc.UUCP (Peter J. Holsberg) writes: >Dumb question: if in an assignment like > x = 3; >where x is declared a double, the 3 is simply widened to the size of a >double, why does this fail? > min = minimum( min, x ); >where > double minimum( double, double ); The key is, the conversion from int to double has to be done by code generated by the compiler, which means that the compiler has to know that it is needed. If you haven't previously declared the function prototype, or if you have declared it a la "old style": double minimum(); , or if you have declared it before the use of the function but your compiler does not fully support (proposed) ANSI C rules for function prototypes, then the types of the function parameters have no effect on the code that is generated to pass the parameters to the function. In such a case, the compiler will simply apply "default widening conventions" (all integer types < long get widened to int, float to double) to the parameters. Then, on the other end the function is always implemented by code that is prepared to receive the correct (widened) parameter types; it never tries to perform further conversions when picking up the parameters. Therefore, the default- widened type must agree with the type declared in the beginning of the actual function definition. The main reason for this rigamarole is to support separate compilation of functions without having to pass type information (known in the trade as "dope vectors") along with the data values for function parameters. In ANSI C as proposed, you'll be able to have function prototypes in scope and thereby get the compiler to automatically convert all parameters to matching types. (Personally I don't think this is a good idea.)