Name

stdio − standard buffered input/output package

Syntax

#include <stdio.h>

FILE *stdin;
FILE *stdout;
FILE *stderr;

Description

The functions described in section 3s constitute a user-level buffering scheme.  The in-line macros getc and putc() handle characters quickly.  The higher level routines gets, fgets, scanf, fscanf, fread, puts, fputs, printf, fprintf, fwrite all use getc and putc; they can be freely intermixed.

A file with associated buffering is called a stream, and is declared to be a pointer to a defined type FILE.  The fopen() subroutine creates certain descriptive data for a stream and returns a pointer to designate the stream in all further transactions. There are three normally open streams with constant pointers declared in the include file and associated with the standard open files:

stdin standard input file

stdout standard output file

stderr standard error file

A constant ‘pointer’ NULL (0) designates no stream at all. 

An integer constant EOF (−1) is returned upon end of file or error by integer functions that deal with streams. 

Any routine that uses the standard input/output package must include the header file <stdio.h> of pertinent macro definitions.  The functions and constants mentioned in sections labeled 3S are declared in the include file and need no further declaration.  The constants, and the following ‘functions’ are implemented as macros; redeclaration of these names is perilous: getc, getchar, putc, putchar, feof, ferror, fileno.

The GFLOAT version of libc is used when you use the cc() command with the −Mg option, or you use the ld() command with the −lcg option.  The GFLOAT version of libc must be used with modules compiled with cc() using the −Mg option. 

Note that neither the compiler nor the linker ld() can detect when mixed double floating point types are used, and the program may produce erroneous results if this occurs.

System V Compatibility

This library contains System V compatibility features that are available to general ULTRIX programs.  For a discussion of how these features are documented, and how to specify that the System V environment is to be used in compiling and linking your programs, see intro(.).

Diagnostics

The value EOF is returned uniformly to indicate that a FILE pointer has not been initialized with fopen, input (output) has been attempted on an output (input) stream, or a FILE pointer designates corrupt or otherwise unintelligible FILE data.

In cases where a large amount of computation is done after printing part of a line on an output terminal, it is necessary to fflush() the standard output before going off and computing so that the output will appear.

Files

/lib/libc.a /usr/lib/libcg.a

See Also

open(2), close(2), read(2), write(2), fread(3s), fseek(3s), ferror(3s), fclose(3s), fopen(3s)