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PROLOG

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

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.1-2008 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

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.1-2008, <stdlib.h>

COPYRIGHT

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 http://www.unix.org/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 .

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