strtoq(3) — Linux manual page


STRTOL(3)                 Linux Programmer's Manual                STRTOL(3)

NAME         top

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

SYNOPSIS         top

       #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

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 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.

       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(), strtoq() │ Thread safety │ MT-Safe locale │

CONFORMING TO         top

       strtol(): POSIX.1-2001, POSIX.1-2008, C89, C99 SVr4, 4.3BSD.

       strtoll(): POSIX.1-2001, POSIX.1-2008, 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 the "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

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 <stdlib.h>
       #include <limits.h>
       #include <stdio.h>
       #include <errno.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]) : 10;

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

           /* Check for various possible errors */

           if ((errno == ERANGE && (val == LONG_MAX || val == LONG_MIN))
                   || (errno != 0 && val == 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),

COLOPHON         top

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GNU                              2020-06-09                        STRTOL(3)