strtol(3) — Linux manual page


strtol(3)               Library Functions Manual               strtol(3)

NAME         top

       strtol, strtoll, strtoq - convert a string to a long integer

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <stdlib.h>

       long strtol(const char *restrict nptr,
                   char **restrict endptr, int base);
       long long strtoll(const char *restrict nptr,
                   char **restrict endptr, int base);

   Feature Test Macro Requirements for glibc (see

               || /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE

DESCRIPTION         top

       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" 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 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.

       The strtoll() function works just like the strtol() function but
       returns a long long integer value.

RETURN VALUE         top

       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).

ERRORS         top

       EINVAL (not in C99) The given base contains an unsupported value.

       ERANGE The resulting value was out of range.

       The implementation may also set errno to EINVAL in case no
       conversion was performed (no digits seen, and 0 returned).

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       │ Interface                    Attribute     Value          │
       │ strtol(), strtoll(),         │ Thread safety │ MT-Safe locale │
       │ strtoq()                     │               │                │

STANDARDS         top

       C11, POSIX.1-2008.

HISTORY         top

              POSIX.1-2001, C89, SVr4, 4.3BSD.

              POSIX.1-2001, C99.

NOTES         top

       Since 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 "C" and "POSIX",
       these functions may accept other, implementation-defined numeric

       BSD also has

           quad_t 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().

EXAMPLES         top

       The 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 <errno.h>
       #include <limits.h>
       #include <stdio.h>
       #include <stdlib.h>

       main(int argc, char *argv[])
           int base;
           char *endptr, *str;
           long val;

           if (argc < 2) {
               fprintf(stderr, "Usage: %s str [base]\n", argv[0]);

           str = argv[1];
           base = (argc > 2) ? atoi(argv[2]) : 0;

           errno = 0;    /* To distinguish success/failure after call */
           val = strtol(str, &endptr, base);

           /* Check for various possible errors. */

           if (errno != 0) {

           if (endptr == str) {
               fprintf(stderr, "No digits were found\n");

           /* If we got here, strtol() successfully parsed a number. */

           printf("strtol() returned %ld\n", val);

           if (*endptr != '\0')        /* Not necessarily an error... */
               printf("Further characters after number: \"%s\"\n", endptr);


SEE ALSO         top

       atof(3), atoi(3), atol(3), strtod(3), strtoimax(3), strtoul(3)

Linux man-pages (unreleased)     (date)                        strtol(3)

Pages that refer to this page: pmstore(1)pmtrace(1)atof(3)atoi(3)scanf(3)sscanf(3)strtod(3)strtoimax(3)strtoul(3)slapo-retcode(5)bpf-helpers(7)