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fopen(3s) [bsd man page]

FOPEN(3S)																 FOPEN(3S)

NAME
fopen, freopen, fdopen - open a stream SYNOPSIS
#include <stdio.h> FILE *fopen(filename, type) char *filename, *type; FILE *freopen(filename, type, stream) char *filename, *type; FILE *stream; FILE *fdopen(fildes, type) char *type; DESCRIPTION
Fopen opens the file named by filename and associates a stream with it. Fopen returns a pointer to be used to identify the stream in sub- sequent operations. Type is a character string having one of the following values: "r" open for reading "w" create for writing "a" append: open for writing at end of file, or create for writing In addition, each type may be followed by a "+" to have the file opened for reading and writing. "r+" positions the stream at the begin- ning of the file, "w+" creates or truncates it, and "a+" positions it at the end. Both reads and writes may be used on read/write streams, with the limitation that an fseek, rewind, or reading an end-of-file must be used between a read and a write or vice-versa. Freopen substitutes the named file in place of the open stream. It returns the original value of stream. The original stream is closed. Freopen is typically used to attach the preopened constant names, stdin, stdout, stderr, to specified files. Fdopen associates a stream with a file descriptor obtained from open, dup, creat, or pipe(2). The type of the stream must agree with the mode of the open file. SEE ALSO
open(2), fclose(3) DIAGNOSTICS
Fopen and freopen return the pointer NULL if filename cannot be accessed, if too many files are already open, or if other resources needed cannot be allocated. BUGS
Fdopen is not portable to systems other than UNIX. The read/write types do not exist on all systems. Those systems without read/write modes will probably treat the type as if the "+" was not present. These are unreliable in any event. In order to support the same number of open files as does the system, fopen must allocate additional memory for data structures using cal- loc after 20 files have been opened. This confuses some programs which use their own memory allocators. An undocumented routine, f_preal- loc, may be called to force immediate allocation of all internal memory except for buffers. 4th Berkeley Distribution May 27, 1986 FOPEN(3S)

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fopen(3UCB)					     SunOS/BSD Compatibility Library Functions					       fopen(3UCB)

NAME
fopen, freopen - open a stream SYNOPSIS
/usr/ucb/cc [ flag ... ] file ... #include <stdio.h> FILE *fopen(file, mode) const char *file, *mode; FILE *freopen(file, mode, iop) const char *file, *mode; register FILE *iop; DESCRIPTION
The fopen() function opens the file specified by file and associates a stream with it. If the open succeeds, fopen() returns a pointer to be used to identify the stream in subsequent operations. The file argument points to a character string that contains the name of the file to be opened. The mode argument is a character string having one of the following values: r open for reading w truncate or create for writing a append: open for writing at end of file, or create for writing r+ open for update (reading and writing) w+ truncate or create for update a+ append; open or create for update at EOF The freopen() function opens the file specified by file and associates the stream pointed to by iop with it. The mode argument is used just as in fopen(). The original stream is closed, regardless of whether the open ultimately succeeds. If the open succeeds, freopen() returns the original value of iop. The freopen() function is typically used to attach the preopened streams associated withstdin, stdout, and stderr to other files. When a file is opened for update, both input and output can be performed on the resulting stream. Output cannot be directly followed by input without an intervening fseek(3C) or rewind(3C). Input cannot be directly followed by output without an intervening fseek(3C) or rewind(3C). An input operation that encounters EOF will fail. RETURN VALUES
The fopen() and freopen() functions return a NULL pointer on failure. USAGE
The fopen() and freopen() functions have transitional interfaces for 64-bit file offsets. See lf64(5). SEE ALSO
cc(1B), open(2), fclose(3C), fopen(3C), freopen(3C), fseek(3C), malloc(3C), rewind(3C), lf64(5) NOTES
Use of these functions should be restricted to applications written on BSD platforms. Use of these functions with any of the system libraries or in multithreaded applications is unsupported. To support the same number of open files as the system, fopen() must allocate additional memory for data structures using malloc(3C) after 64 files have been opened. This confuses some programs that use their own memory allocators. The fopen() and freopen() functions differ from the standard I/O functions fopen(3C) and freopen(3C). The standard I/O functions distin- guish binary from text files with an additional use of 'b' as part of the mode, enabling portability of fopen(3C) and freopen(3C) beyond SunOS 4.x systems. SunOS 5.11 30 Oct 2007 fopen(3UCB)

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