|MATLAB Function Reference|
Open a file or obtain information about open files
fid = fopen(filename)
opens the file
filename for read access. (On PCs,
fopen opens files for binary read access.)
fid is a scalar MATLAB integer, called a file identifier. You use the
fid as the first argument to other file input/output routines. If
fopen cannot open the file, it returns
-1. Two file identifiers are automatically available and need not be opened. They are
fid=1 (standard output) and
fid=2 (standard error).
fid = fopen(filename,permission)
opens the file
filename in the mode specified by
permission can be:
||Open file for reading (default).
||Open file, or create new file, for writing; discard existing contents, if any.
||Open file, or create new file, for writing; append data to the end of the file.
||Open file for reading and writing.
||Open file, or create a new file, for reading and writing; discard existing contents, if any.
||Open file, or create new file, for reading and writing; append data to the end of the file.
||Append without automatic flushing; used with tape drives
||Write without automatic flushing; used with tape drives
filename can be a
MATLABPATH relative partial pathname if the file is opened for reading only. A relative path is always searched for first with respect to the current directory. If it is not found and reading only is specified or implied then fopen does an additional search of the
Files can be opened in binary mode (the default) or in text mode. In binary mode, no characters are singled out for special treatment. In text mode on the PC, , the carriage return character preceding a newline character is deleted on input and added before the newline character on output. To open in text mode, add "t" to the permission string, for example
'wt+'. (On Unix, text and binary mode are the same so this has no effect. But on PC systems this is critical.)
If the file is opened in update mode ('+'), an input command like |
[fid,message] = fopen(filename,permission)
opens a file as above. If it cannot open the file,
message contains a system-dependent error message. If
fopen successfully opens a file, the value of
message is empty.
[fid,message] = fopen(filename,permission,machineformat) opens the specified file with the specified
permission and treats data read using
fread or data written using
fwrite as having a format given by
machineformat is one of the following strings:
|Cray floating point with big-endian byte ordering
|IEEE floating point with big-endian byte ordering
|IEEE floating point with little-endian byte ordering
|IEEE floating point with big-endian byte ordering and 64-bit long data type
|IEEE floating point with little-endian byte ordering and 64-bit long data type
|Numeric format of the machine on which MATLAB is running (the default).
|VAX D floating point and VAX ordering
|VAX G floating point and VAX ordering
fids = fopen('all')
returns a row vector containing the file identifiers of all open files, not including
2 (standard output and standard error). The number of elements in the vector is equal to the number of open files.
[filename,permission,machineformat] = fopen(fid)
permission string, and
machineformat string associated with the specified file. An invalid
fid returns empty strings for all output arguments.
'A' permissions are designed for use with tape drives and do not automatically perform a flush of the current output buffer after output operations. For example, open a 1/4" cartridge tape on a SPARCstation for writing with no auto-flush:
The example uses
fopen to open a file and then passes the
fid, returned by
fopen, to other file I/O functions to read data from the file and then close the file.