NAME

fopen(), freopen(), fdopen() − open or re-open a stream file; convert file to stream

SYNOPSIS

#include <stdio.h>

FILE *fopen(const char *pathname, const char *type);

FILE *freopen(const char *pathname, const char *type, FILE *stream);

FILE *fdopen(int fildes, const char *type);

DESCRIPTION

fopen() Opens the file named by pathname and associates a stream with it.  fopen() returns a pointer to the FILE structure associated with the stream.

freopen() substitutes the named file in place of the open stream. The original stream is closed, regardless of whether the open ultimately succeeds.  freopen() returns a pointer to the FILE structure associated with stream and makes an implicit call to clearerr() (see ferror(3S)).

freopen() is typically used to attach the preopened streams associated with stdin, stdout, and stderr to other files. 

fdopen() associates a stream with a file descriptor.  File descriptors are obtained from open(), dup(), creat(), or pipe() (see open(2), dup(2), creat(2), and pipe(2)), which open files but do not return pointers to a FILE structure stream.  Streams are necessary input for many of the Section (3S) library routines.  The type of stream must agree with the mode of the open file.  The meanings of type used in the fdopen() call are exactly as specified above, except that w, w+, wb, and wb+ do not cause truncation of the file. 

pathname Points to a character string containing the name of the file to be opened. 

type Character string having one of the following values:

r open for reading

w truncate to zero length or create for writing

a append; open for writing at end of file, or create for writing

rb open binary file for reading

wb truncate to zero length or create binary file for writing

ab append; open binary file for writing at end-of-file, or create binary file

r+ open for update (reading and writing)

w+ truncate to zero length or create for update

a+ append; open or create for update at end-of-file

r+b or rb+ open binary file for update (reading and writing)

w+b or wb+ truncate to zero length or create binary file for update

a+b or ab+ append; open or create binary file for update at end-of-file

When a file is opened for update, both input and output can be done on the resulting stream. However, output cannot be directly followed by input without an intervening call to fflush() or to a file positioning function (fseek(), fsetpos(), or rewind()), and input cannot be directly followed by output without an intervening call to a file positioning function unless the input operation encounters end-of-file. 

When a file is opened for append (i.e., when type is a or a+), it is impossible to overwrite information already in the file.  All output is written at the end of the file, regardless of intervening calls to fseek().  If two separate processes open the same file for append, each process can write freely to the file without fear of destroying output being written by the other.  Output from the two processes will be intermixed in the file in the order in which it is written. 

RETURN VALUE

Upon successful completion, fopen(), fdopen(), and freopen() return a FILE * pointer to the stream.  Otherwise, a null pointer is returned and errno is set to indicate the error. 

ERRORS

fopen(), fdopen(), and freopen() fail if:

[EINVAL] The type argument is not a valid mode. 

[ENOMEM] There is insufficient space to allocate a buffer. 

fopen() and freopen() fail if:

[EACCES] Search permission is denied on a component of the path prefix, or the file exists and the permissions specified by type are denied, or the file does not exist and write permission is denied for the parent directory of the file to be created. 

[EINTR] A signal was caught during fopen() or freopen().  function. 

[EISDIR] The named file is a directory and type requires write access. 

[EMFILE] The calling process has attempted to exceed its open file limit. 

[ENAMETOOLONG]
The length of the pathname string exceeds PATH_MAX or a pathname component is longer than NAME_MAX while POSIX_NO_TRUNC is in effect. 

[ENFILE] The system file table is full. 

[ENOENT] The named file does not exist or the pathname argument points to an empty string. 

[ENOSPC] The directory or file system that would contain the new file cannot be expanded, the file does not exist, and it was to be created. 

[ENOTDIR] A component of the path prefix is not a directory. 

[ENXIO] The named file is a character special or block special file, and the device associated with the special file does not exist. 

[EROFS] The named file resides on a read-only file system and type requires write access. 

Additional errno values can be set by the underlying open() call made from the fopen() and freopen() functions (see open(2)). 

NOTES

HP-UX binary file types are equivalent to their non-binary counterparts.  For example, types r and rb are equivalent. 

SEE ALSO

creat(2), dup(2), open(2), pipe(2), fclose(3S), fseek(3S), popen(3S), setvbuf(3S). 

STANDARDS CONFORMANCE

fopen(): AES, SVID2, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

fdopen(): AES, SVID2, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1

freopen(): AES, SVID2, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

Hewlett-Packard Company  —  HP-UX Release 9.0: August 1992