why is strtof is always evaluating to HUGE_VAL?

Question

What could be the issue here? It doesn't matter what number I choose for str, it is always 26815615859885194199148049996411692254958731641184786755447122887443528060147093953603748596333806855380063716372972101707507765623893139892867298012168192.00

char *str = "2.6";
printf("%f\n", strtof(str, (char**)NULL));
//prints 26815615859885194199148049996411692254958731641184786755447122887443528060147093953603748596333806855380063716372972101707507765623893139892867298012168192.00

whole program:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
    char *str = "2.6";
    printf("%f\n", strtof(str, NULL));
    return 1;
}

compile with -Wall:

test4.c:7: warning: implicit declaration of function âstrtofâ

Answer 1

Perhaps you've forgotten to include the correct header(s)?

#include <stdlib.h>
#include <stdio.h>

int main() {
    printf("%f\n", strtof("2.6", NULL));
    return 0;
}

produces:

2.600000

for me...

Answer 2

What platform are you building for/on? The warning that you say is being emitted:

test4.c:7: warning: implicit declaration of function âstrtofâ

indicates that the compiler doesn't know that strtof() returns a float, so it's going to push an int to the printf() call instead of a double. strtof() is normally declared in stdlib.h, which you're including. But it wasn't a standard function until C99, so the exact compiler platform (and configuration/options you're using) may affect whether it's being made available or not.

Answer 3

strtof is defined in C99 only. It may be that passing the option -std=c99 to the compiler will fix it since default GCC (-std=gnu89) includes only a few C99 features.

Another option is to use the C89-kosher strtod. Which is probably the better option in the long run, anyways. (When do you need singles except in exceptional circumstances?)

Answer 4

Given your warnings, you should try adding -std=c99 to get the C99 standard definitions from the header. By default it will assume that the return value is an int and then try to convert that to a float. This will obviously be wrong. Alternatively you could simply supply your own, correct declaration for strtof().

Answer 5

As the others have said, you need -std=c99. But you can also use strtod() which is string to double, and you don't need -std=c99 for that.

I was having problems with strtof() on CentOS 5.5 with glibc 2.5 unless I used -std=c99, but strtod() worked perfectly.