strtol man page on Archlinux

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

       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)):

	   _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
	   or cc -std=c99

       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 deter‐
       mined 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
       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.

       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

       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).

   Multithreading (see pthreads(7))
       The strtol(), strtoll(), and strtoq() functions	are  thread-safe  with
       exceptions.  These functions can be safely used in multithreaded appli‐
       cations, as long as setlocale(3) is not called  to  change  the	locale
       during their execution.

       strtol() conforms to SVr4, 4.3BSD, C89, C99, and POSIX.1-2001, and str‐
       toll() to C99 and POSIX.1-2001.

       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	deter‐
       mine if an error occurred by checking whether errno has a nonzero value
       after the call.

       According to POSIX.1-2001, 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 str‐

       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 pro‐
       duced 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);


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

       This page is part of release 3.65 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at

GNU				  2014-03-18			     STRTOL(3)

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