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.1‐2017 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.1‐2017, stdlib.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  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               2017                          ATOI(3P)

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