The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group

#### NAME

> stderr, stdin, stdout - standard I/O streams

#### SYNOPSIS

> ``#include <stdio.h>
> extern FILE *stderr, *stdin, *stdout;
> ``

#### DESCRIPTION

> [CX] 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.

> 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.

> [CX] 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.

#### RETURN VALUE

> None.

#### ERRORS

> No errors are defined.

The following sections are informative.

#### EXAMPLES

> None.

#### APPLICATION USAGE

> None.

#### RATIONALE

> None.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> fclose, feof, ferror, fileno, fopen, fprintf, fread, fscanf, fseek, getc, gets, popen, putc, puts, read, setbuf, setvbuf, tmpfile, ungetc, vfprintf

> XBD <stdio.h>, <unistd.h>

#### CHANGE HISTORY

> First released in Issue 1.

#### Issue 6

> Extensions beyond the ISO C standard are marked.

> A note that stderr is expected to be open for reading and writing is added to the DESCRIPTION.

End of informative text.

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