.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved .TH "FOPEN" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual" .\" fopen .SH NAME fopen \- open a stream .SH SYNOPSIS .LP \fB#include .br .sp FILE *fopen(const char *restrict\fP \fIfilename\fP\fB, const char *restrict\fP \fImode\fP\fB); .br \fP .SH DESCRIPTION .LP The \fIfopen\fP() function shall open the file whose pathname is the string pointed to by \fIfilename\fP, and associates a stream with it. .LP The \fImode\fP 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. .TP 7 \fIr\fP\ or\ \fIrb\fP Open file for reading. .TP 7 \fIw\fP\ or\ \fIwb\fP Truncate to zero length or create file for writing. .TP 7 \fIa\fP\ or\ \fIab\fP Append; open or create file for writing at end-of-file. .TP 7 \fIr+\fP\ or\ \fIrb+\fP\ or\ \fIr+b\fP Open file for update (reading and writing). .TP 7 \fIw+\fP\ or\ \fIwb+\fP\ or\ \fIw+b\fP Truncate to zero length or create file for update. .TP 7 \fIa+\fP\ or\ \fIab+\fP\ or\ \fIa+b\fP Append; open or create file for update, writing at end-of-file. .sp .LP The character \fB'b'\fP shall have no effect, but is allowed for ISO\ C standard conformance. Opening a file with read mode (\fIr\fP as the first character in the \fImode\fP argument) shall fail if the file does not exist or cannot be read. .LP Opening a file with append mode (\fIa\fP as the first character in the \fImode\fP argument) shall cause all subsequent writes to the file to be forced to the then current end-of-file, regardless of intervening calls to \fIfseek\fP(). .LP When a file is opened with update mode ( \fB'+'\fP as the second or third character in the \fImode\fP 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 \fIfflush\fP() or to a file positioning function ( \fIfseek\fP(), \fIfsetpos\fP(), or \fIrewind\fP()), 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. .LP 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. .LP If \fImode\fP is \fIw\fP, \fIwb\fP, \fIa\fP, \fIab\fP, \fIw\fP+, \fIwb\fP+, \fIw\fP+\fIb\fP, \fIa\fP+, \fIab\fP+, or \fIa\fP+\fIb\fP, and the file did not previously exist, upon successful completion, the \fIfopen\fP() function shall mark for update the \fIst_atime\fP, \fIst_ctime\fP, and \fIst_mtime\fP fields of the file and the \fIst_ctime\fP and \fIst_mtime\fP fields of the parent directory. .LP If \fImode\fP is \fIw\fP, \fIwb\fP, \fIw\fP+, \fIwb\fP+, or \fIw\fP+\fIb\fP, and the file did previously exist, upon successful completion, \fIfopen\fP() shall mark for update the \fIst_ctime\fP and \fIst_mtime\fP fields of the file. The \fIfopen\fP() function shall allocate a file descriptor as \fIopen\fP() does. .LP After a successful call to the \fIfopen\fP() function, the orientation of the stream shall be cleared, \ the encoding rule shall be cleared, and the associated \fBmbstate_t\fP object shall be set to describe an initial conversion state. .LP The largest value that can be represented correctly in an object of type \fBoff_t\fP shall be established as the offset maximum in the open file description. .SH RETURN VALUE .LP Upon successful completion, \fIfopen\fP() shall return a pointer to the object controlling the stream. Otherwise, a null pointer shall be returned, \ and \fIerrno\fP shall be set to indicate the error. .SH ERRORS .LP The \fIfopen\fP() function shall fail if: .TP 7 .B EACCES Search permission is denied on a component of the path prefix, or the file exists and the permissions specified by \fImode\fP are denied, or the file does not exist and write permission is denied for the parent directory of the file to be created. .TP 7 .B EINTR A signal was caught during \fIfopen\fP(). .TP 7 .B EISDIR The named file is a directory and \fImode\fP requires write access. .TP 7 .B ELOOP A loop exists in symbolic links encountered during resolution of the \fIpath\fP argument. .TP 7 .B EMFILE {OPEN_MAX} file descriptors are currently open in the calling process. .TP 7 .B ENAMETOOLONG .sp The length of the \fIfilename\fP argument exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}. .TP 7 .B ENFILE The maximum allowable number of files is currently open in the system. .TP 7 .B ENOENT A component of \fIfilename\fP does not name an existing file or \fIfilename\fP is an empty string. .TP 7 .B 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. .TP 7 .B ENOTDIR A component of the path prefix is not a directory. .TP 7 .B ENXIO The named file is a character special or block special file, and the device associated with this special file does not exist. .TP 7 .B EOVERFLOW The named file is a regular file and the size of the file cannot be represented correctly in an object of type \fBoff_t\fP. .TP 7 .B EROFS The named file resides on a read-only file system and \fImode\fP requires write access. .sp .LP The \fIfopen\fP() function may fail if: .TP 7 .B EINVAL The value of the \fImode\fP argument is not valid. .TP 7 .B ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the \fIpath\fP argument. .TP 7 .B EMFILE {FOPEN_MAX} streams are currently open in the calling process. .TP 7 .B EMFILE {STREAM_MAX} streams are currently open in the calling process. .TP 7 .B ENAMETOOLONG .sp Pathname resolution of a symbolic link produced an intermediate result whose length exceeds {PATH_MAX}. .TP 7 .B ENOMEM Insufficient storage space is available. .TP 7 .B ETXTBSY The file is a pure procedure (shared text) file that is being executed and \fImode\fP requires write access. .sp .LP \fIThe following sections are informative.\fP .SH EXAMPLES .SS Opening a File .LP The following example tries to open the file named \fBfile\fP for reading. The \fIfopen\fP() function returns a file pointer that is used in subsequent \fIfgets\fP() and \fIfclose\fP() calls. If the program cannot open the file, it just ignores it. .sp .RS .nf \fB#include \&... FILE *fp; \&... void rgrep(const char *file) { \&... if ((fp = fopen(file, "r")) == NULL) return; \&... } \fP .fi .RE .SH APPLICATION USAGE .LP None. .SH RATIONALE .LP None. .SH FUTURE DIRECTIONS .LP None. .SH SEE ALSO .LP \fIfclose\fP() , \fIfdopen\fP() , \fIfreopen\fP() , the Base Definitions volume of IEEE\ Std\ 1003.1-2001, \fI\fP .SH COPYRIGHT 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 .