C Error: undefined reference to '_itoa'

Question

I'm trying to convert an integer to a character to write to a file, using this line:

fputc(itoa(size, tempBuffer, 10), saveFile);

and I receive this warning and message:

warning: implicit declaration of 'itoa'

undefined reference to '_itoa'

I've already included stdlib.h, and am compiling with:

gcc -Wall -pedantic -ansi

Any help would be appreciated, thank you.

Answer 1

itoa is not part of the standard. I suspect either -ansi is preventing you from using it, or it's not available at all.

I would suggest using sprintf()

If you go with the c99 standard, you can use snprintf() which is of course safer.

char buffer[12];
int i = 20;
snprintf(buffer, 12,"%d",i);

Answer 2

This here tells you that during the compilation phase itoa is unknown:

warning: implicit declaration of 'itoa'

so if this function is present on your system you are missing a header file that declares it. The compiler then supposes that it is a function that takes an unspecific number of arguments and returns an int.

This message from the loader phase

undefined reference to '_itoa'

explains that also the loader doesn't find such a function in any of the libraries he knows of.

So you should perhaps follow Brian's advice to replace itoa by a standard function.