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    <p>The only actual error is that you don't check the return value of <code>malloc</code> for null.</p> <p>The name <code>itoa</code> is kind of already taken for a function that's non-standard, but not that uncommon. It doesn't allocate memory, rather it writes to a buffer provided by the caller:</p> <pre><code>char *itoa(int value, char * str, int base); </code></pre> <p>If you don't want to rely on your platform having that, I would still advise following the pattern. String-handling functions which return newly allocated memory in C are generally more trouble than they're worth in the long run, because most of the time you end up doing further manipulation, and so you have to free lots of intermediate results. For example, compare:</p> <pre><code>void delete_temp_files() { char filename[20]; strcpy(filename, "tmp_"); char *endptr = filename + strlen(filename); for (int i = 0; i &lt; 10; ++i) { itoa(endptr, i, 10); // itoa doesn't allocate memory unlink(filename); } } </code></pre> <p>vs.</p> <pre><code>void delete_temp_files() { char filename[20]; strcpy(filename, "tmp_"); char *endptr = filename + strlen(filename); for (int i = 0; i &lt; 10; ++i) { char *number = itoa(i, 10); // itoa allocates memory strcpy(endptr, number); free(number); unlink(filename); } } </code></pre> <p>If you had reason to be especially concerned about performance (for instance if you're implementing a stdlib-style library including <code>itoa</code>), or if you were implementing bases that <code>sprintf</code> doesn't support, then you might consider not calling <code>sprintf</code>. But if you want a base 10 string, then your first instinct was right. There's absolutely nothing "incorrect" about the <code>%d</code> format specifier.</p> <p>Here's a possible implementation of <code>itoa</code>, for base 10 only:</p> <pre><code>char *itobase10(char *buf, int value) { sprintf(buf, "%d", value); return buf; } </code></pre> <p>Here's one which incorporates the snprintf-style approach to buffer lengths:</p> <pre><code>int itobase10n(char *buf, size_t sz, int value) { return snprintf(buf, sz, "%d", value); } </code></pre>
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    1. POWhat is the proper way of implementing a good "itoa()" function?
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    1. USSteve Jessop
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    1. POWhat is the proper way of implementing a good "itoa()" function?
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    1. COThis is silly, if he's not returning allocated memory, then why not just call snprintf directly. `snprintf(endptr, bytes, "%d", number)` - This would prevent a temporary variable declaration and doesn't have those buffer overflow possibilities in this sample code.
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    2. CO@evilclown: the reason not to call `snprintf` directly the is the same reason anyone ever writes a function: to abstract the operation specifically of converting an integer to a string, as opposed to any of the many things which `snprintf` can do with different string formats. There is only a buffer overflow possibility in this code on platforms where `int` is at least 48 bits, and I think that issue has been covered well elsewhere. Feel free to merge one of those into this answer :-)
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    3. COAnyway, snprintf is often over-rated. If you're worried about buffer overflows, and your solution is to use snprintf, then why aren't you worried about truncating the result string and getting the wrong answer? A "secure" program which doesn't actually work is of course better than an insecure program which doesn't work, but still not great ;-p
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