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File: HuntTheBug ''' <img src="/cgi-bin/CountHits.py?HuntTheBug" alt="" /> From ColinsBlog, and one of the RandomWritings. ---- !!! Let's play Hunt the Bug ... [[[>50 {{{ #include <stdio.h> #include <string.h> #include <stdlib.h> int main( void ) { float f; double d; f = strtof("5.7",NULL); d = strtod("5.7",NULL); printf("F: %f\n", f); printf("F: %f\n",(double)f); printf("D: %f\n", d); printf("D: %f\n",(double)d); return 0; } }}} ]]] OK, so here's a fun thing - what do you think that code should print? It prints this: * F: 3565158.000000 * F: 3565158.000000 * D: 5.700000 * D: 5.700000 That surprised me. In case you're interested: * gcc version 4.1.0 (SUSE Linux) * SUSE LINUX 10.1 (i586) * VERSION = 10.1 It works with this command: * gcc -std=c99 bug.c So here's the thing. [[[>50 I've been corrected about this. Apparently it's not thought of as being "built in" if the code is in *libc.* So I stand (or sit) corrected. The code for *strtof* is in *libc,* or some library (as yet not exactly pinned down) but the prototype isn't in *strlib.h.* The reason is becoming clear now. *strtof* wasn't in the original C and has only been introduced in C99. Since it is in C99 the code exists. Since it's not in earlier versions the prototype isn't declared unless you're in C99 mode. So there you are. ]]] Apparently GCC has a built-in version of *strtof,* (corrected - see side-box) which it compiles into your code if you're not using C99. (Because before C99 there was no *strtof* in the standard library). However, the built-in version of *strtof* doesn't have a prototype unless you are in C99 mode, just in case you made one of your own, and hence the system defaults to returning an *int.*. But now one part of the compiler thinks it's an int, another thinks it's a float, and everything goes to hell in a handbasket. So there are three ways to get answers you expect instead of random numbers: * Compile with the c99 option as above, * Provide a prototype: float strtof(char *, char * *); * Use doubles. The moral? Always use *-Wall* Or don't use C.