FOPEN(3s,L)                 AIX Technical Reference                 FOPEN(3s,L)



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fopen, freopen, fdopen



PURPOSE

Opens a stream.

LIBRARY

Standard I/O Library (libc.a)

SYNTAX

#include <stdio.h>



                FILE *fopen (path, type)    FILE *fdopen (fildes, type)
                char *path, *type;          int fildes;
                                            char *type;
                FILE *freopen (path, type, stream)
                char *path, *type;
                FILE *stream;



DESCRIPTION

The fopen subroutine opens the file named by the path parameter and associates
a stream with it.  fopen returns a pointer to the FILE structure of this
stream.

The path parameter points to a character string that contains the name of the
file to be opened.

The type parameter points to a character string that has one of the following
values:

"r"   Open the file for reading
"w"   Truncate or create a new file 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 end of file)

The freopen subroutine substitutes the named file in place of the open stream.
The original stream is closed whether or not the open succeeds.  freopen
returns a pointer to the FILE structure associated with stream.  The freopen
subroutine is typically used to attach the pre-opened streams associated with
stdin, stdout, and stderr to other files.



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FOPEN(3s,L)                 AIX Technical Reference                 FOPEN(3s,L)




The fdopen subroutine associates a stream with a file descriptor obtained from
an open, dup, creat, or pipe system call.  These system calls open files but do
not return pointers to FILE structures.  Many of the standard I/O library
subroutines require pointers to FILE structures.  Note that the type of stream
specified must agree with the mode of the open file.

When you open a file for update, you can perform both input and output
operations on the resulting stream.  However, an output operation cannot be
directly followed by an input operation without an intervening fseek or rewind.
Also, an input operation cannot be directly followed by an output operation
without an intervening fseek, rewind, or an input operation that encounters the
end of the file.

When you open a file for append (that is, when type is "a" or "a+"), it is
impossible to overwrite information already in the file.  You can use fseek to
reposition the file pointer to any position in the file, but when output is
written to the file, the current file pointer is ignored.  All output is
written at the end of the file and causes the file pointer to be repositioned
to the end of the output.

If two separate processes open the same file for append, each process can write
freely to the file without destroying the output being written by the other.
The output from the two processes is intermixed in the order in which it is
written to the file.  Note that if the data is buffered, then it is not
actually written until it is flushed.

If the fopen or freopen subroutine fails, a NULL pointer is returned.

ERROR CONDITIONS

The fopen and freopen subroutines fail if one or more of the following are
true:

EACCES    Search permission is denied on a component of the path prefix, or the
          file exists and the permissions specified by mode 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 the fopen function.

EISDIR    The named file is a directory and mode requires write access.

EMFILE    FOPEN_MAX file descriptors, directories and message catalogs are
          currently open in the calling process.

ENAMETOOLONG
          The length of the filename string exceeds PATH_MAX or a pathname
          component is longer than NAME_MAX.

ENFILE    The system file table is full.




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FOPEN(3s,L)                 AIX Technical Reference                 FOPEN(3s,L)



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

ENOSPC    The directory or file system that would contain the new file cannot
          be expanded; the file that was to be created does not exist.

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 this special file does not exist.

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

EINVAL    The value of the mode argument is not valid.

ENOMEM    Insufficient storage space is available.

ETXTBSY   The file is a pure procedure (shared text) file that is being
          executed and mode requires write access.

The fdopen subroutine fails if one or more of the following is true:

EBADF     The fildes argument is not a valid file descriptor.

EINVAL    The mode argument is not a valid mode.

ENOMEM    Insufficient space to allocate a buffer.

RELATED INFORMATION

In this book:  "fclose, fflush," "fseek, rewind, ftell," "open, openx, creat,"
"setbuf, setvbuf," and "stdio."






















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