Write End Of File (EOF)

Hi, everybody, I want to make a program to read a file (this file has already information), and set the End of File in any part of the file, is it possible?

Answer 1

[Walter Roberson]

MATLAB does not have any way to set a true End of File if it is smaller than the original file (but files can be lengthened.)

You could fwrite() a control-Z, also known as EOF (End of File), if that is meaningful for you (which would require MS Windows and reading the file in "text" mode)

Answer 2

[Iain]

If by EOF you mean the ascii code "4", all you need to do is fwrite(fid,4,'uint8'); on the open file.

You can do the same with any other end of file marker provided you know its binary value.

[Jan]

As Walter has pointed out already: This works only under Windows and when the file is opened in text mode.

[Walter Roberson]

4 is EOT (End of Transmission), control-D, which is used interactively on Unix-type systems to indicate end-of-file, but is never used as end-of-file when stored in files on Unix-type systems.

MS Windows uses ^Z (26) interactively to indicate end-of-file, and MS-DOS also used it stored in text files to indicate end-of-file. MS Windows reading in text mode (where the line terminator is CR LF pair) also often treat a stored ^Z as end-of-file; when MS Windows is not using that compatibility mode, there is no stored character that indicates end-of-file.

^Z as end-of-file is historical, and goes back to DEC's RSX-11 and to CPM, and I do not know were else. Ah, Wikipedia says it was borrowed from CPM.

Answer 3

[Jan]

I've been very surprised, that there is in fact no method to reduce the size of the file in Matlab except for:

Create a new file
Copy the contents until the wanted end
Delete the old file
Rename the new file

Under Matlab 6.5 this was horribly slow, because these commands have been forwarded to DOS calls.

Finally I had done this by a C-Mex: FEX: FileResize

[Walter Roberson]

See also http://stackoverflow.com/questions/873454/how-to-truncate-a-file-in-c

The truncate() call is part of POSIX, not part of the C library, and MATLAB tends to omit functionality that is not part of the C library (even though they no longer support any non-POSIX system)

MATLAB also messes up the POSIX behavior for extending a file by fseek() to after the end of file and writing there; the fseek() stops at end of file instead.