NAME
fopen, fdopen, freopen - stream open functions
SYNOPSIS
#include <stdio.h> FILE *fopen(const char *path, const char *mode); FILE *fdopen(int fd, const char *mode); FILE *freopen(const char *path, const char *mode, FILE *stream); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): fdopen(): _POSIX_C_SOURCE
DESCRIPTION
The fopen() function opens the file whose name is the string pointed to by path and associates a stream with it. The argument mode points to a string beginning with one of the following sequences (possibly followed by additional characters, as described below): r Open text file for reading. The stream is positioned at the beginning of the file. r+ Open for reading and writing. The stream is positioned at the beginning of the file. w Truncate file to zero length or create text file for writing. The stream is positioned at the beginning of the file. w+ Open for reading and writing. The file is created if it does not exist, otherwise it is truncated. The stream is positioned at the beginning of the file. a Open for appending (writing at end of file). The file is created if it does not exist. The stream is positioned at the end of the file. a+ Open for reading and appending (writing at end of file). The file is created if it does not exist. The initial file position for reading is at the beginning of the file, but output is always appended to the end of the file. The mode string can also include the letter 'b' either as a last character or as a character between the characters in any of the two- character strings described above. This is strictly for compatibility with C89 and has no effect; the 'b' is ignored on all POSIX conforming systems, including Linux. (Other systems may treat text files and binary files differently, and adding the 'b' may be a good idea if you do I/O to a binary file and expect that your program may be ported to non-UNIX environments.) See NOTES below for details of glibc extensions for mode. Any created files will have mode S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH (0666), as modified by the process's umask value (see umask(2)). Reads and writes may be intermixed on read/write streams in any order. Note that ANSI C requires that a file positioning function intervene between output and input, unless an input operation encounters end-of- file. (If this condition is not met, then a read is allowed to return the result of writes other than the most recent.) Therefore it is good practice (and indeed sometimes necessary under Linux) to put an fseek(3) or fgetpos(3) operation between write and read operations on such a stream. This operation may be an apparent no-op (as in fseek(..., 0L, SEEK_CUR) called for its synchronizing side effect). Opening a file in append mode (a as the first character of mode) causes all subsequent write operations to this stream to occur at end-of-file, as if preceded the call: fseek(stream, 0, SEEK_END); The fdopen() function associates a stream with the existing file descriptor, fd. The mode of the stream (one of the values "r", "r+", "w", "w+", "a", "a+") must be compatible with the mode of the file descriptor. The file position indicator of the new stream is set to that belonging to fd, and the error and end-of-file indicators are cleared. Modes "w" or "w+" do not cause truncation of the file. The file descriptor is not dup'ed, and will be closed when the stream created by fdopen() is closed. The result of applying fdopen() to a shared memory object is undefined. The freopen() function opens the file whose name is the string pointed to by path and associates the stream pointed to by stream with it. The original stream (if it exists) is closed. The mode argument is used just as in the fopen() function. The primary use of the freopen() function is to change the file associated with a standard text stream (stderr, stdin, or stdout).
RETURN VALUE
Upon successful completion fopen(), fdopen() and freopen() return a FILE pointer. Otherwise, NULL is returned and errno is set to indicate the error.
ERRORS
EINVAL The mode provided to fopen(), fdopen(), or freopen() was invalid. The fopen(), fdopen() and freopen() functions may also fail and set errno for any of the errors specified for the routine malloc(3). The fopen() function may also fail and set errno for any of the errors specified for the routine open(2). The fdopen() function may also fail and set errno for any of the errors specified for the routine fcntl(2). The freopen() function may also fail and set errno for any of the errors specified for the routines open(2), fclose(3), and fflush(3).
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7). Interface Attribute Value fopen(), fdopen(), freopen() Thread safety MT-Safe
CONFORMING TO
fopen(), freopen(): POSIX.1-2001, POSIX.1-2008, C89, C99. fdopen(): POSIX.1-2001, POSIX.1-2008.
NOTES
Glibc notes The GNU C library allows the following extensions for the string specified in mode: c (since glibc 2.3.3) Do not make the open operation, or subsequent read and write operations, thread cancellation points. This flag is ignored for fdopen(). e (since glibc 2.7) Open the file with the O_CLOEXEC flag. See open(2) for more information. This flag is ignored for fdopen(). m (since glibc 2.3) Attempt to access the file using mmap(2), rather than I/O system calls (read(2), write(2)). Currently, use of mmap(2) is attempted only for a file opened for reading. x Open the file exclusively (like the O_EXCL flag of open(2)). If the file already exists, fopen() fails, and sets errno to EEXIST. This flag is ignored for fdopen(). In addition to the above characters, fopen() and freopen() support the following syntax in mode: ,ccs=string The given string is taken as the name of a coded character set and the stream is marked as wide-oriented. Thereafter, internal conversion functions convert I/O to and from the character set string. If the ,ccs=string syntax is not specified, then the wide-orientation of the stream is determined by the first file operation. If that operation is a wide-character operation, the stream is marked wide-oriented, and functions to convert to the coded character set are loaded.
BUGS
When parsing for individual flag characters in mode (i.e., the characters preceding the "ccs" specification), the glibc implementation of fopen() and freopen() limits the number of characters examined in mode to 7 (or, in glibc versions before 2.14, to 6, which was not enough to include possible specifications such as "rb+cmxe"). The current implementation of fdopen() parses at most 5 characters in mode.
SEE ALSO
open(2), fclose(3), fileno(3), fmemopen(3), fopencookie(3), open_memstream(3)
COLOPHON
This page is part of release 4.09 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
More Linux Commands
manpages/XSetWindowAttributes.3.html
XSetWindowAttributes(3) - create windows and window attribut
XSetWindowAttributes.3 - The XCreateWindow function creates an unmapped subwindow for a specified parent window, returns the window ID of the created window, an
manpages/gnutls_x509_crt_get_crl_dist_points.3.html
gnutls_x509_crt_get_crl_dist_points(3) - API function.......
This function retrieves the CRL distribution points (2.5.29.31), contained in the given certificate in the X509v3 Certificate Extensions. reason_flags should be
manpages/glCullFace.3gl.html
glCullFace(3gl) - specify whether front- or back-facing face
glCullFace specifies whether front- or back-facing facets are culled (as specified by mode) when facet culling is enabled. Facet culling is initially disabled.
manpages/form_init.3form.html
form_init(3form) - set hooks for automatic invocation by app
These functions make it possible to set hook functions to be called at various points in the automatic processing of input event codes by form_driver. The funct
manpages/gnutls_x509_crl_verify.3.html
gnutls_x509_crl_verify(3) - API function - Linux man page...
This function will try to verify the given crl and return its status. See gnutls_x509_crt_list_verify() for a detailed description of return values. RETURNS On
manpages/Tk_TextWidth.3.html
Tk_TextWidth(3) - routines to measure and display simple sin
These routines are for measuring and displaying simple single-font, single-line strings. To measure and display single-font, multi-line, justified text, refer t
manpages/sasl_client_start.3.html
sasl_client_start(3) - Begin an authentication negotiation
sasl_client_start() selects a mechanism for authentication and starts the authentication session. The mechlist is the list of mechanisms the client might like t
manpages/new_menu.3menu.html
new_menu(3menu) - create and destroy menus - Linux man page
The function new_menu creates a new menu connected to a specified item pointer array (which must be NULL-terminated). The function free_menu disconnects menu fr
manpages/Exporter.3pm.html
Exporter(3pm) - Implements default import method for modules
The Exporter module implements an import method which allows a module to export functions and variables to its users namespaces. Many modules use Exporter rathe
manpages/XGetWindowAttributes.3.html
XGetWindowAttributes(3) - get current window attribute or ge
The XGetWindowAttributes function returns the current attributes for the specified window to an XWindowAttributes structure. It returns a nonzero status on succ
manpages/Ttk_RelievePadding.3.html
Ttk_RelievePadding(3) - Tk themed geometry utilities........
The Ttk_Box structure represents a rectangular region of a window: typedef struct { int x; int y; int width; int height; } Ttk_Box; All coordinates are relative
manpages/wbkgdset.3ncurses.html
wbkgdset(3ncurses) - curses window background manipulation r
The bkgdset and wbkgdset routines manipulate the background of the named window. The window background is a chtype consisting of any combination of attributes (
