strtol() - convert string value to a long integer
#include <stdlib.h>
#include <limits.h>
long strtol (char *nptr, char **endptr, int base)
The strtol(3) function converts the string in nptr to a long value.
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 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 or a represents 10, B or
b represents 11, and so forth, with Z or
z representing 35.)
If endptr is not NULL, strtol(3) stores the address of
the first invalid character in *endptr. If there were no
digits at all, however, strtol(3) 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(3) function returns the result of the conversion, unless the value would underflow or overflow. If an underflow occurs, strtol(3) returns {LONG_MIN.} If an overflow occurs, strtol(3) returns LONG_MAX. In both cases, errno is set.
The strtol(3) function can fail for any of these reasons:
atof(3)
atoi(3)
atol(3)
strtod(3)
strtoul(3)