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HP-UX 11i Version 3: February 2007

Technical documentation

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stdio() — standard buffered input/output stream file package


#include <stdio.h>


The Standard I/O functions described in the subsection (3S) entries of this manual constitute an efficient, user-level I/O buffering scheme. The getc() and putc() functions handle characters quickly. The following functions all use or act as if they use getc() and putc(), and can be freely intermixed:

fgetc() fputs() getchar() putchar() fgets() fread() gets() puts() fprintf() fscanf() getw() putw() fputc() fwrite() printf() scanf()

A file with associated buffering is called a stream and is declared to be a pointer to a defined type FILE. fopen() creates certain descriptive data for a stream and returns a pointer to designate the stream in all further transactions. Section (3S) library routines operate on this stream.

At program startup, three streams, standard input, standard output, and standard error, are predefined and do not need to be explicitly opened. When opened, the standard input and standard output streams are fully buffered if the output refers to a file and line-buffered if the output refers to a terminal. The standard error output stream is by default unbuffered. These three streams have the following constant pointers declared in the <stdio.h> header file :


standard input file


standard output file


standard error file

A constant, NULL, (0) designates a nonexistent pointer.

An integer-constant, EOF, (-1) is returned upon end-of-file or error by most integer functions that deal with streams (see individual descriptions for details).

An integer constant BUFSIZ specifies the size of the buffers used by the particular implementation (see setbuf(3S)).

Any program that uses this package must include the header file of pertinent macro definitions as follows:

#include <stdio.h>

The functions and constants mentioned in subsection (3S) entries of this manual are declared in that header file and need no further declaration.

A constant _NFILE defines the default maximum number of open files allowed per process. To increase the open file limit beyond this default value, see getrlimit(2).


Use of stdio interfaces with a shared read/write file descriptor on non-positional devices will provide undefined behavior. Applications which are doing stdio operations on non-positional devices need to use seperate file pointers for input and output, even if using the same file descriptor for both types of operations.


Invalid stream pointers usually cause grave disorder, possibly including program termination. Individual function descriptions describe the possible error conditions.


stderr: AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

stdin: AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

stdout: AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

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