Set errno for any of the errors specified for the routine The fopen(), fdopen(), and freopen() functions may also fail and Otherwise, NULL is returned and errno isĮRRORS top EINVAL The mode provided to fopen(), fdopen(), or freopen() was Upon successful completion fopen(), fdopen(), and freopen() The primary use of the freopen() function is to change the fileĪssociated with a standard text stream ( stderr, stdin, or Mode are permitted (if any), and under what circumstances. It is implementation-defined which changes of Stream need not be closed if the call to freopen() In this case, the file descriptor associated with the Specification for this behavior was added in the C99 standard, Reopens the pathname that is associated with the stream. Mode of the stream to that specified in mode that is, freopen() If the pathname argument is a null pointer, freopen() changes the The mode argument is used just as in the fopen() function. The original stream (if it exists) is closed. Pointed to by pathname and associates the stream pointed to by The freopen() function opens the file whose name is the string The result of applying fdopen() to a shared memory object is Will be closed when the stream created by fdopen() is closed. Stream is set to that belonging to fd, and the error and end-of-įile indicators are cleared. "r+", "w", "w+", "a", "a+") must be compatible with the mode of The mode of the stream (one of the values "r", The fdopen() function associates a stream with the existing fileĭescriptor, fd. The file descriptor associated with the stream is opened as if byĪ call to open(2) with the following flags: Opening a file in append mode ( a as the first character of mode)Ĭauses all subsequent write operations to this stream to occur at This operation may be an apparent no-op (as in fseek(., 0L, SEEK_CUR) called for its synchronizing side effect). Operation between write and read operations on such a stream. Sometimes necessary under Linux) to put an fseek(3) or fsetpos(3) The most recent.) Therefore it is good practice (and indeed Then a read is allowed to return the result of writes other than Note that ANSI C requires that a file positioningįunction intervene between output and input, unless an input Reads and writes may be intermixed on read/write streams in any S_IWGRP | S_IROTH | S_IWOTH (0666), as modified by the process's See NOTES below for details of glibc extensions for mode.Īny created file will have the mode S_IRUSR | S_IWUSR | S_IRGRP | That your program may be ported to non-UNIX environments.) 'b' may be a good idea if you do I/O to a binary file and expect May treat text files and binary files differently, and adding the This is strictly forĬompatibility with ISO C and has no effect the 'b' is ignored onĪll POSIX conforming systems, including Linux. The mode string can also include the letter 'b' either as a lastĬharacter or as a character between the characters in any of the Initial file position for reading is at the end of the On what the initial read position is when using this mode.įor glibc, the initial file position for reading is at theīeginning of the file, but for Android/BSD/MacOS, the Output isĪlways appended to the end of the file. The file is created if it does not exist. The stream is positioned atĪ+ Open for reading and appending (writing at end of file). The stream isĪ Open for appending (writing at end of file). The file is created if itĭoes not exist, otherwise it is truncated. The stream is positioned at the beginning of the W Truncate file to zero length or create text file for The argument mode points to a string beginning with one of theįollowing sequences (possibly followed by additional characters, Pointed to by pathname and associates a stream with it. The fopen() function opens the file whose name is the string SYNOPSIS top #include FILE *fopen(const char *restrict pathname, const char *restrict mode ) FILE *fdopen(int fd, const char * mode ) FILE *freopen(const char *restrict pathname, const char *restrict mode, FILE *restrict stream ) įeature Test Macro Requirements for glibc (see Fopen(3) Library Functions Manual fopen(3) NAME topįopen, fdopen, freopen - stream open functions
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