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



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

NAME
       atoi -- convert a string to an integer

SYNOPSIS
       #include <stdlib.h>

       int atoi(const char *str);

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

ERRORS
       No errors are defined.

       The following sections are informative.

EXAMPLES
   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);
           }
           ...

APPLICATION USAGE
       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
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       strtol()

       The Base Definitions volume of POSIX.1-2017, <stdlib.h>

COPYRIGHT
       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 http://www.opengroup.org/unix/online.html .

       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
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                              ATOI(3)
