strtol (3) - Linux Man Pages
strtol: convert a string to a long integer
strtol, strtoll, strtoq - convert a string to a long integer
#include <stdlib.h> 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)):
|| /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
DESCRIPTIONThe 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" or "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 uppercase or lowercase 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 '\0' but **endptr is '\0' on return, the entire string is valid.
RETURN VALUEThe 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).
- (not in C99) The given base contains an unsupported value.
- The resulting value was out of range.
ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7).
|strtol(), strtoll(), strtoq()||Thread safety||MT-Safe locale|
CONFORMING TOstrtol(): POSIX.1-2001, POSIX.1-2008, C89, C99 SVr4, 4.3BSD.
NOTESSince strtol() can legitimately return 0, LONG_MAX, or LONG_MIN (LLONG_MAX or LLONG_MIN for strtoll()) on both success and failure, the calling program should set errno to 0 before the call, and then determine if an error occurred by checking whether errno has a nonzero value after the call.
According to POSIX.1, in locales other than the "C" and "POSIX", these functions may accept other, implementation-defined numeric strings.
BSD also has
quad_t strtoq(const char *nptr, char **endptr, int base);
EXAMPLEThe program shown below demonstrates the use of strtol(). The first command-line argument specifies a string from which strtol() should parse a number. The second (optional) argument specifies the base to be used for the conversion. (This argument is converted to numeric form using atoi(3), a function that performs no error checking and has a simpler interface than strtol().) Some examples of the results produced by this program are the following:
$ ./a.out 123 strtol() returned 123 $ ./a.out ' 123' strtol() returned 123 $ ./a.out 123abc strtol() returned 123 Further characters after number: abc $ ./a.out 123abc 55 strtol: Invalid argument $ ./a.out '' No digits were found $ ./a.out 4000000000 strtol: Numerical result out of range
Program source#include <stdlib.h> #include <limits.h> #include <stdio.h> #include <errno.h>
main(int argc, char *argv)
This page is part of release 5.05 of the Linux
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at