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.

Puiia

I am guessing that itoa may not be present in the standard C library you are using. You could try specifying the flag -fpermissive to see if the code works. – Shin

There's no such function as itoa in the "official" standard library. Apparently the standard library you are using does not provide itoa. Your -pedantic and -ansi flags will not help anything. Quite the opposite, they can actually make things worse by hiding non-standard functions (I don't know whether they really do that). Try compiling without them. – Latency

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);

Artamas

You need a bigger buffer to handle the negative sign. – Effort

@RocketRoy it was actually simply an example. The value 20 in the example fits just fine in a char[10] and that's the buffer size the OP was using. But yes, a signed 32 bit int would require char[12] to handle the sign and \0 – Artamas

@BrianRoach while you are perfectly correct, for the sake of people who like to copy paste I have changed the size of the buffer in the example. – Kooky

Brian's original answer illustrates the fact of the matter. Assuming that int would fit into a 12 byte string is completely incorrect, and if put out as fact, it could mislead people. For example, on AVR 8-bit systems, 'int's are often 16-bit (2- byte). – Madrid

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.

Bosket