STRTOL(3) Linux Programmer's Manual STRTOL(3)
strtol, strtoll, strtoq - convert a string to a long integer.
strtol(const char *nptr, char **endptr, int base);
long long int
strtoll(const char *nptr, char **endptr, int base);
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 must 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 ` ' but **endptr is ` ' on return, the
entire string is valid.
The strtoll() function works just like the strtol() function but returns a long long integer value.
The strtol() function returns the result of the conversion, unless the value would underflow or overflow. If an underflow occurs, strtol()
returns LONG_MIN. If an overflow occurs, strtol() returns LONG_MAX. In both cases, errno is set to ERANGE. Precisely the same holds for
strtoll() (with LLONG_MIN and LLONG_MAX instead of LONG_MIN and LONG_MAX).
ERANGE The resulting value was out of range.
EINVAL (not in C99) The given base contains an unsupported value.
The implementation may also set errno to EINVAL in case no conversion was performed (no digits seen, and 0 returned).
In locales other than the "C" locale, also other strings may be accepted. (For example, the thousands separator of the current locale may
BSD also has
strtoq(const char *nptr, char **endptr, int base);
with completely analogous definition. Depending on the wordsize of the current architecture, this may be equivalent to strtoll() or to
strtol() conforms to SVID 3, BSD 4.3, ISO 9899 (C99) and POSIX, and strtoll() to ISO 9899 (C99) and POSIX-2001.
atof(3), atoi(3), atol(3), strtod(3), strtoul(3)