How to make sure completion of a write to file

Within a function B (which is called from another function A) I am using multiple fprintf commands to print a matrix to a file. The file is opened and closed inside the function B. In faster machines it happens that the matrix does not finish printing, however the function B terminates and gives back control to the calling function A.

I have noticed that despite the fclose commmand at the end of function B, the file is still open when controls returns to calling function A. And if A does not close the file I can stil write to it or close it from the Matlab console. If I do that (closing from console) then all missing data is flushed to the file, but if I don't (for example if I quit Matlab) then a piece of the matrix will never be printed. Opening as 'w' or 'W' does not make any difference.

I have found a workaround: opening in A and passing the file id as parameter to function B, let function B do the printing and closing the file in A. This way insures that the whole matrix is printed, but it is very inconvenient because the function B should print in a large number of files (names changing all the time) and this workaround limits my ability to use it as expected.

I would appreciate some help.

Answer 1

[Walter Roberson]

In theory, if you perform any fseek() operation on the output file, it should flush. At least that is what the standards say for the underlying POSIX fseek() operation; I am not certain that it works that way for MATLAB.

Could I suggest that you experiment with using an onCleanup() to close the file? That would catch any cases where the function somehow returned early before reaching the fclose() in your logic.

[Art]

Thaks for the suggestions, but I do not see how could I use any of them: fseek is just for read modus, but I am only writing. cleanup is an specific function of Code Composer Studio, how could I use it here? Looking at cleanup I have found other two functions that could be useful: execute and run, but again, I don't see how to use them in a simple function call.

[Walter Roberson]

fseek() is not just for read modes: you can fseek() on any stream. fseek() to 0 bytes relative to current position if you need to.

onCleanup() has nothing to do with code composer. The "on" is part of the name.

Answer 2

[Art]

I have found another workaround. Doing a fclose('all') in calling function A just before it finishes, solves the issue: the offending file is flushed and closed. But the situation seems to be a Matlab bug. The fclose in function B is in fact never reached, but control is returned to function A.

Although this workaround works, there are really a number of files open (all the files open by function B) until function A closes them all.

I would appreciate a comment from some Matlab developer.