STRTOL(3) Linux Programmer's Manual STRTOL(3)
strtol, strtoll, strtoq - convert a string to a long integer
long int strtol(const char *nptr, char **endptr, int base);
long long int strtoll(const char *nptr, char **endptr, int base);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
XOPEN_SOURCE >= 600 || _BSD_SOURCE || _SVID_SOURCE || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99
The strtol() function converts the initial part of the string in nptr to a long integer value 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 long int 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, strtol()
stores the original value of nptr in *endptr (and returns 0). In particular, if *nptr is not '