On Sat, Jul 14, 2007 at 12:52:09PM -0400, Michael Velez wrote:
I've got this little program I wrote to test something, and it keeps giving the wrong result. I'm not inexperienced in C, but I can't believe strtof (et al) are broken, so I must be doing something wrong. However, I've spent hours looking at this and comparing it to the man pages and don't see what I'm doing wrong. strtod() and strtold() also give equally wrong results. (the example program given on the strotd man page works fine, BTW.)
Can someone wield a clue-bat please? :)
Here's the program:
#include <stdio.h> #include <math.h> #include <stdlib.h> #include <errno.h>
int main (int argc, char ** argv) { float ldbl = 0.0; char * endp;
printf ("%s\n", argv[1]);
errno = 0; ldbl = strtof (argv[1], &endp); if (errno != 0) printf ("strtof failed! errno=%d\n", errno);
printf ("%f\n", (double) ldbl); printf ("%f\n", (double) strtof (argv[1], (char **)NULL)); printf ("%f\n", (double) atof (argv[1]));
return 0; }
Compile it with:
cc -O0 -g -o x4 x4.c
then run it like this:
./x4 2.5
and I'd EXPECT it to produce this output:
2.5 2.5 2.5 2.5
but it actually produces this:
2.5 1075838976.000000 1075838976.000000 2.500000
the typecase of the arg in the 3 printf calls makes no difference. Remove it and the results are the same.
Using an input of something other than 2.5 changes the middle two lines in some way in which I haven't yet discerned a pattern, but the result is still highly bogus.
The following strtod line works fine on my system (CentOS 5, latest updates, x86_64):
printf ("%lf\n", (double) strtod (argv[1], (char **)NULL));
For strtof, the SYNOPSIS in the man page mentions you need to add:
#define _ISO_C99_SOURCE
Or
#define _XOPEN_SOURCE 600
Either line should be added before ALL include files (note there is a mistake in the synopsis. There should be no = sign in the define statement for _XOPEN_SOURCE).
The above #define lines enforces C99 compatibility rules, which is the revised ISO C standard which came out in 1999. As a previous responder suggested, you can also specify -std=gnu99 or -std=C99 on the compile line.
Michael
Sorry, I forgot to mention that I'm using Centos 4.5. And the man page here doesn't mention those #define settings. I'll give it a try, thanks!