Itoa

Itoa is a non-standard, non-portable function used in some C libraries to convert an integer value to a null-terminated string in a specified base. It is not part of the C standard library, but it has been widely provided by various compilers and environments.

Common signature and variations include functions such as char *itoa(int value, char *str, int base), with variations for long or unsigned long. The function usually returns a pointer to the output buffer specified by str. The base parameter typically ranges from 2 to 36, using digits 0-9 and letters (a-z or A-Z) to represent values above 9.

Behavior with negative values varies by implementation. For base 10, it is common to prepend a minus sign for negative numbers. For bases other than 10, handling of negative values is implementation-dependent and may involve treating the value as unsigned or applying a sign in a non-standard way.

Algorithmic notes include that itoa often builds digits from least significant to most significant, writing them into the buffer in reverse order and then reversing the relevant portion to form the final string. The caller must ensure the output buffer is large enough to hold all digits, a possible sign, and the terminating null character.

Portability and alternatives: because itoa is not part of the C standard, portable code should avoid relying on it. Alternatives include using snprintf or sprintf with appropriate formatting (for decimal, "%d" or "%u"), or, in C++, using std::to_string or string streams. For cross-platform projects, a custom integer-to-string function or a portable library is often preferred.