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       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.


       atoi — convert a string to an integer


       #include <stdlib.h>

       int atoi(const char *str);


       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.


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


       No errors are defined.

       The following sections are informative.


   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.







       The Base Definitions volume of POSIX.1‐2008, <stdlib.h>


       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 .