How to convert an integer to a string portably?

I was looking for a way to convert an integer to a string in a portable manner (portable among at least Windows & Linux and x86 and x86_64) and I though itoa(X) to be standard just like atoi(1).

But I read the开发者_开发知识库 following in the Wikipedia entry:

The itoa function is a widespread non-standard extension to the standard C programming language. It cannot be portably used, as it is not defined in any of the C language standards; however, compilers often provide it through the header while in non-conforming mode, because it is a logical counterpart to the standard library function atoi.

So I'd like to know if there is any way to do it in a portable manner or not. In case I have to write my own function, which things do I have to be careful with?

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Most often you just use printf("%d");

http://en.wikipedia.org/wiki/Printf

You can use sprintf if you need it in a buffer, but how often do you convert to a string and not write it to a file or output device?

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If you aren't doing this terribly often, how about a runtime library routine that writes a few numbers to memory, analyzes the results and stores an encoding type? From then on you just switch on your "encoding type" to select which conversion routine to use.