snprintf

snprintf is a function in the C standard library that formats a sequence of characters and stores them in the character array pointed to by str. It is designed to prevent buffer overflows by enforcing a maximum number of characters to write, as specified by the size parameter. The function follows the printf formatting rules and formats the provided arguments according to the format string.

It writes at most size-1 characters from the formatted output and always terminates the destination with a null character, provided size is nonzero. The return value is the number of characters that would have been written if enough space had been available, not counting the terminating null terminator. If the returned value is greater than or equal to size, the output was truncated.

Special case: if size is 0, nothing is written, but snprintf still returns the length of the would-be output. The function is part of the printf family and has a related variant, vsnprintf, which accepts a va_list instead of variadic arguments.

snprintf is defined in the C99 standard and is widely implemented across platforms, including GNU C Library, musl, BSD libc, and MSVC. It is commonly used as a safer alternative to functions like sprintf when the destination buffer size is known, enabling formatted output without risking buffer overflow.