Originální popis anglicky:
fopen - open a stream
Návod, kniha: POSIX Programmer's Manual
#include <stdio.h>
FILE *fopen(const char *restrict
filename, const
char *restrict mode);
The
fopen() function shall open the file whose pathname is the string
pointed to by
filename, and associates a stream with it.
The
mode argument points to a string. If the string is one of the
following, the file shall be opened in the indicated mode. Otherwise, the
behavior is undefined.
- r or rb
- Open file for reading.
- w or wb
- Truncate to zero length or create file for writing.
- a or ab
- Append; open or create file for writing at
end-of-file.
- r+ or rb+ or r+b
- Open file for update (reading and writing).
- w+ or wb+ or w+b
- Truncate to zero length or create file for update.
- a+ or ab+ or a+b
- Append; open or create file for update, writing at
end-of-file.
The character
'b' shall have no effect, but is allowed for ISO C
standard conformance. Opening a file with read mode (
r as the first
character in the
mode argument) shall fail if the file does not exist
or cannot be read.
Opening a file with append mode (
a as the first character in the
mode argument) shall cause all subsequent writes to the file to be
forced to the then current end-of-file, regardless of intervening calls to
fseek().
When a file is opened with update mode (
'+' as the second or third
character in the
mode argument), both input and output may be performed
on the associated stream. However, the application shall ensure that output is
not directly followed by input without an intervening call to
fflush()
or to a file positioning function (
fseek(),
fsetpos(), or
rewind()), and input is not directly followed by output without an
intervening call to a file positioning function, unless the input operation
encounters end-of-file.
When opened, a stream is fully buffered if and only if it can be determined not
to refer to an interactive device. The error and end-of-file indicators for
the stream shall be cleared.
If
mode is
w,
wb,
a,
ab,
w+,
wb+,
w+
b,
a+,
ab+, or
a+
b,
and the file did not previously exist, upon successful completion, the
fopen() function shall mark for update the
st_atime,
st_ctime, and
st_mtime fields of the file and the
st_ctime and
st_mtime fields of the parent directory.
If
mode is
w,
wb,
w+,
wb+, or
w+
b, and the file did previously exist, upon successful
completion,
fopen() shall mark for update the
st_ctime and
st_mtime fields of the file. The
fopen() function shall allocate
a file descriptor as
open() does.
After a successful call to the
fopen() function, the orientation of the
stream shall be cleared, the encoding rule shall be cleared, and the
associated
mbstate_t object shall be set to describe an initial
conversion state.
The largest value that can be represented correctly in an object of type
off_t shall be established as the offset maximum in the open file
description.
Upon successful completion,
fopen() shall return a pointer to the object
controlling the stream. Otherwise, a null pointer shall be returned,
and
errno shall be set to indicate the error.
The
fopen() function shall fail if:
- 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 fopen().
- EISDIR
- The named file is a directory and mode requires
write access.
- ELOOP
- A loop exists in symbolic links encountered during
resolution of the path argument.
- EMFILE
- {OPEN_MAX} file descriptors are currently open in the
calling process.
- ENAMETOOLONG
-
The length of the filename argument exceeds {PATH_MAX} or a pathname
component is longer than {NAME_MAX}.
- ENFILE
- The maximum allowable number of files is currently open in
the system.
- ENOENT
- A component of filename does not name an existing
file or filename is an empty string.
- ENOSPC
- The directory or file system that would contain the new
file cannot be expanded, the file does not exist, and the file 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 this special file does not
exist.
- EOVERFLOW
- The named file is a regular file and the size of the file
cannot be represented correctly in an object of type off_t.
- EROFS
- The named file resides on a read-only file system and
mode requires write access.
The
fopen() function may fail if:
- EINVAL
- The value of the mode argument is not valid.
- ELOOP
- More than {SYMLOOP_MAX} symbolic links were encountered
during resolution of the path argument.
- EMFILE
- {FOPEN_MAX} streams are currently open in the calling
process.
- EMFILE
- {STREAM_MAX} streams are currently open in the calling
process.
- ENAMETOOLONG
-
Pathname resolution of a symbolic link produced an intermediate result whose
length exceeds {PATH_MAX}.
- 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 following sections are informative.
The following example tries to open the file named
file for reading. The
fopen() function returns a file pointer that is used in subsequent
fgets() and
fclose() calls. If the program cannot open the file,
it just ignores it.
#include <stdio.h>
...
FILE *fp;
...
void rgrep(const char *file)
{
...
if ((fp = fopen(file, "r")) == NULL)
return;
...
}
None.
None.
None.
fclose() ,
fdopen() ,
freopen() , the Base Definitions
volume of IEEE Std 1003.1-2001,
<stdio.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
