The strtol function converts the string in nptr to a
.Vt long value. The strtoll function converts the string in nptr to a
.Vt "long long" value. The strtoimax function converts the string in nptr to an
.Vt intmax_t value. The strtoq function converts the string in nptr to a
.Vt quad_t value. The conversion is done according to the given base, which must be between 2 and 36 inclusive, or be the special value 0.
The string may begin with an arbitrary amount of white space (as determined by isspace(3)) followed by a single optional + or - sign. If base is zero or 16, the string may then include a "0x" prefix, and the number will be read in base 16; otherwise, a zero base is taken as 10 (decimal) unless the next character is 0, in which case it is taken as 8 (octal).
The remainder of the string is converted to a
.Vt long , "long long" , intmax_t or
.Vt quad_t value in the obvious manner, stopping at the first character which is not a valid digit in the given base. (In bases above 10, the letter A in either upper or lower case represents 10, B represents 11, and so forth, with Z representing 35.)
If endptr is not NULL, strtol stores the address of the first invalid character in *endptr. If there were no digits at all, however, strtol stores the original value of nptr in *endptr. (Thus, if *nptr is not \0 but **endptr is \0 on return, the entire string was valid.)
The strtol, strtoll, strtoimax and strtoq functions return the result of the conversion, unless the value would underflow or overflow. If no conversion could be performed, 0 is returned and the global variable errno is set to EINVAL (the last feature is not portable across all platforms). If an overflow or underflow occurs, errno is set to ERANGE and the function return value is clamped according to the following table.