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

       For an explanation of the terms used in this section, see attributes(7).
       ┌──────────────────────────────────────────────────────────────────────┬───────────────┬────────────────┐
       │ Interface                                                            │ Attribute     │ Value          │
       ├──────────────────────────────────────────────────────────────────────┼───────────────┼────────────────┤
       │ strtol(), strtoll(), strtoq()                                        │ Thread safety │ MT-Safe locale │
       └──────────────────────────────────────────────────────────────────────┴───────────────┴────────────────┘

       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==ERANGE after the call.

       If  the  base  needs  to  be  tested, it should be tested in a call where the string is known to succeed.
       Otherwise, it's impossible to portably differentiate the errors.

           errno = 0;
           strtol("0", NULL, base);
           if (errno == EINVAL)
               goto unsupported_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 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,  and  the  base is supported, 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 longlong integer value.

       This function does not modify errno on success.

       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).

       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.out123
           strtol() returned 123
           $ ./a.out'123'
           strtol() returned 123
           $ ./a.out123abc
           strtol() returned 123
           Further characters after number: "abc"
           $ ./a.out123abc55
           strtol: Invalid argument
           $ ./a.out''
           No digits were found
           $ ./a.out4000000000
           strtol: Numerical result out of range

   Programsource

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

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

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

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

           errno = 0;    /* To distinguish success/failure after call */
           strtol("0", NULL, base);
           if (errno == EINVAL) {
               perror("strtol");
               exit(EXIT_FAILURE);
           }

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

           /* Check for various possible errors. */

           if (errno == ERANGE) {
               perror("strtol");
               exit(EXIT_FAILURE);
           }

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

           /* 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);

           exit(EXIT_SUCCESS);
       }

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

       strtoll()
              POSIX.1-2001, C99.

       Standard C library (libc, -lc)

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

       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).

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

Linux man-pages 6.9.1                              2024-06-16                                          strtol(3)

       C11, POSIX.1-2008.

#include<stdlib.h>longstrtol(constchar*restrictnptr,char**_Nullablerestrictendptr,intbase);longlongstrtoll(constchar*restrictnptr,char**_Nullablerestrictendptr,intbase);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       strtoll():
           _ISOC99_SOURCE
               || /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE

       According  to  POSIX.1,  in  locales  other  than  "C"  and  "POSIX",  these  functions may accept other,
       implementation-defined numeric strings.

       BSD also has

           quad_tstrtoq(constchar*nptr,char**endptr,intbase);

       with completely analogous definition.  Depending on the wordsize of the current architecture, this may be
       equivalent to strtoll() or to strtol().