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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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STDIN(3P) POSIX Programmer's Manual STDIN(3P)
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.
stderr, stdin, stdout — standard I/O streams
#include <stdio.h>
extern FILE *stderr, *stdin, *stdout;
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.
A file with associated buffering is called a stream and is
declared to be a pointer to a defined type FILE. The fopen()
function shall create certain descriptive data for a stream and
return a pointer to designate the stream in all further
transactions. Normally, there are three open streams with constant
pointers declared in the <stdio.h> header and associated with the
standard open files.
At program start-up, three streams shall be predefined and need
not be opened explicitly: standard input (for reading conventional
input), standard output (for writing conventional output), and
standard error (for writing diagnostic output). When opened, the
standard error stream is not fully buffered; the standard input
and standard output streams are fully buffered if and only if the
stream can be determined not to refer to an interactive device.
The following symbolic values in <unistd.h> define the file
descriptors that shall be associated with the C-language stdin,
stdout, and stderr when the application is started:
STDIN_FILENO Standard input value, stdin. Its value is 0.
STDOUT_FILENO Standard output value, stdout. Its value is 1.
STDERR_FILENO Standard error value, stderr. Its value is 2.
The stderr stream is expected to be open for reading and writing.
None.
No errors are defined.
The following sections are informative.
None.
None.
None.
None.
fclose(3p), feof(3p), ferror(3p), fileno(3p), fopen(3p),
fprintf(3p), fread(3p), fscanf(3p), fseek(3p), getc(3p), gets(3p),
popen(3p), putc(3p), puts(3p), read(3p), setbuf(3p), setvbuf(3p),
tmpfile(3p), ungetc(3p), vfprintf(3p)
The Base Definitions volume of POSIX.1‐2017, stdio.h(0p),
unistd.h(0p)
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 STDIN(3P)
Pages that refer to this page: stdio.h(0p), assert(3p), fileno(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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