atoi(3p) — Linux manual page


ATOI(3P)                  POSIX Programmer's Manual                 ATOI(3P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior), or
       the interface may not be implemented on Linux.

NAME         top

       atoi — convert a string to an integer

SYNOPSIS         top

       #include <stdlib.h>

       int atoi(const char *str);

DESCRIPTION         top

       The functionality described on this reference page is aligned with
       the ISO C standard. Any conflict between the requirements described
       here and the ISO C standard is unintentional. This volume of
       POSIX.1‐2008 defers to the ISO C standard.

       The call atoi(str) shall be equivalent to:

           (int) strtol(str, (char **)NULL, 10)

       except that the handling of errors may differ. If the value cannot be
       represented, the behavior is undefined.

RETURN VALUE         top

       The atoi() function shall return the converted value if the value can
       be represented.

ERRORS         top

       No errors are defined.

       The following sections are informative.

EXAMPLES         top

   Converting an Argument
       The following example checks for proper usage of the program. If
       there is an argument and the decimal conversion of this argument
       (obtained using atoi()) is greater than 0, then the program has a
       valid number of minutes to wait for an event.

           #include <stdlib.h>
           #include <stdio.h>
           int minutes_to_event;
           if (argc < 2 || ((minutes_to_event = atoi (argv[1]))) <= 0) {
              fprintf(stderr, "Usage: %s minutes\n", argv[0]); exit(1);


       The atoi() function is subsumed by strtol() but is retained because
       it is used extensively in existing code. If the number is not known
       to be in range, strtol() should be used because atoi() is not
       required to perform any error checking.

RATIONALE         top




SEE ALSO         top


       The Base Definitions volume of POSIX.1‐2008, stdlib.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) In the event of any discrepancy between this version and
       the original IEEE and The Open Group Standard, the original IEEE and
       The Open Group Standard is the referee document. The original
       Standard can be obtained online at .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see .

IEEE/The Open Group                 2013                            ATOI(3P)

Pages that refer to this page: stdlib.h(0p)