Fall '06

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UNIX man pages : stdio (3)

STDIO(3S)							     STDIO(3S)


stdio - standard buffered input/output package


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


The functions described in the entries of sub-class 3S of this manual constitute an efficient, user-level I/O buffering scheme. The in-line macros getc and putc handle characters quickly. The macros getchar and putchar, and the higher-level routines fgetc, fgets, fprintf, fputc, fputs, fread, fscanf, fwrite, gets, getw, printf, puts, putw, and scanf all use or act as if they 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. fopen(3S) creates certain descriptive data for a stream and returns 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 file and associated with the standard open files: stdin standard input file stdout standard output file stderr standard error file The following symbolic values in <unistd.h> define the file descriptors that will be associated with the C-language stdin, stdout and stderr when the application is started: STDIN_FILENO Standard input value, stdin. It has the value of 0. STDOUT_FILENO Standard output value, stdout. It has the value of 1. STDERR_FILENO Standard error value, stderr. It has the value of 2. 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 the individual descriptions for details). An integer constant BUFSIZ specifies the size of the buffers used by the particular implementation. An integer constant FILENAME_MAX specifies the size needed for an array of char large enough to hold the longest file name string that the implementation guarantees can be opened. An integer constant FOPEN_MAX specifies the minimum number of files that the implementation guarantees can be open simultaneously. Note that no more than 255 files may be opened via fopen, and only file descriptors 0 through 255 are valid. 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 the entries of sub-class 3S of this manual are declared in that header 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, ferror, feof, clearerr, and fileno. Output streams, with the exception of the standard error stream stderr, are by default buffered if the output refers to a file and line-buffered if the output refers to a terminal. The standard error output stream stderr is by default unbuffered, but use of freopen [see fopen(3S)] will cause it to become buffered or line-buffered. When an output stream is unbuffered, information is queued for writing on the destination file or terminal as soon as written; when it is buffered, many characters are saved up and written as a block. When it is line-buffered, each line of output is queued for writing on the destination terminal as soon as the line is completed (that is, as soon as a new-line character is written or terminal input is requested). setbuf(3S) or setvbuf(3S) in setbuf(3S) may be used to change the stream's buffering strategy.


Invalid stream pointers will usually cause grave disorder, possibly including program termination. Individual function descriptions describe the possible error conditions.
1994 Man-cgi 1.11, Panagiotis Christias <>
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CSEE | 201 | 201 F'06 | lectures | news | help