.TH STDIO 3S "19 January 1983" .UC 4 .SH NAME stdio \- standard buffered input/output package .SH SYNOPSIS .B #include <stdio.h> .PP .SM .B FILE .B *stdin; .br .SM .B FILE .B *stdout; .br .SM .B FILE .B *stderr; .SH DESCRIPTION The functions described in Sections 3S constitute a user-level buffering scheme. The in-line macros .I getc and .IR putc (3) handle characters quickly. The higher level routines .IR gets , .IR fgets , .IR scanf , .IR fscanf , .IR fread , .IR puts , .IR fputs , .IR printf , .IR fprintf , .IR fwrite all use .I getc and .IR putc ; they can be freely intermixed. .PP A file with associated buffering is called a .I stream, and is declared to be a pointer to a defined type .SM .B FILE. .IR Fopen (3) 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: .TP 10n .BR stdin standard input file .br .ns .TP .B stdout standard output file .br .ns .TP .BR stderr standard error file .PP A constant `pointer' .SM .B NULL (0) designates no stream at all. .PP An integer constant .SM .B EOF (\-1) is returned upon end of file or error by integer functions that deal with streams. .PP 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: .I getc, .I getchar, .I putc, .I putchar, .I feof, .I ferror, .IR fileno . .SH "SEE ALSO" open(2), close(2), read(2), write(2), fread(3), fseek(3), f*(3) .SH DIAGNOSTICS The value .SM .B EOF is returned uniformly to indicate that a .SM .B FILE pointer has not been initialized with .I fopen, input (output) has been attempted on an output (input) stream, or a .SM .B FILE pointer designates corrupt or otherwise unintelligible .SM .B FILE data. .PP For purposes of efficiency, this implementation of the standard library has been changed to line buffer output to a terminal by default and attempts to do this transparently by flushing the output whenever a .IR read (2) from the standard input is necessary. This is almost always transparent, but may cause confusion or malfunctioning of programs which use standard i/o routines but use .IR read (2) themselves to read from the standard input. .PP In cases where a large amount of computation is done after printing part of a line on an output terminal, it is necessary to .IR fflush (3) the standard output before going off and computing so that the output will appear. .SH BUGS The standard buffered functions do not interact well with certain other library and system functions, especially \fIvfork\fP and \fIabort\fP.