strnlen

strnlen is a function in C programming that calculates the length of a string, but with a limit on the number of characters to check. It is defined in the string.h header file. The function takes two arguments: a pointer to the null-terminated string and an unsigned integer representing the maximum number of characters to count.

Unlike the standard strlen function, which continues counting characters until it encounters the null terminator ('\0'), strnlen stops counting if it reaches the specified maximum length, even if the null terminator has not yet been found. This is particularly useful when dealing with strings that might be malformed or corrupted, preventing buffer overflows or infinite loops that could occur if a null terminator is missing.

The return value of strnlen is the number of characters counted, up to the specified maximum length. If the null terminator is found within the specified limit, the function returns the index of the null terminator, which is effectively the length of the string. If the limit is reached before the null terminator is found, the function returns the maximum length that was provided. This behavior ensures that strnlen never reads beyond the specified boundary, making it a safer option in certain scenarios.