strtol

strtol is a function in the C standard library that converts the initial portion of the string pointed to by nptr to a long int. It is declared in stdlib.h as long int strtol(const char *nptr, char **endptr, int base).

Behavior: The function discards leading whitespace, accepts an optional sign, and then interprets as many valid digits as fit in a long int according to the specified base. If base is 0, the base is auto-detected: a 0x or 0X prefix yields base 16; a leading 0 yields base 8; otherwise base 10. If endptr is not NULL, it is set to point to the character immediately following the number; if no conversion is performed, endptr is set to nptr and the function returns 0.

Return value and error handling: If the parsed value lies within the range of long int, that value is returned. If the value would overflow or underflow, LONG_MAX or LONG_MIN is returned and errno is set to ERANGE. The function does not modify the input string. It is the caller’s responsibility to check errno and endptr to detect a failed or partial conversion.

Notes: The base must be 0 or between 2 and 36 inclusive; values outside that range yield undefined behavior. strtol is commonly used with errno and endptr to perform robust input parsing in portable C code. Related functions include strtoul (for unsigned long) and strtol variants for other integer types. See also: strtoul, strtol_l, and strtoll for broader integer parsing.