Closes a file handle.
new; cls; // Create 'mydata' matrix mydata = seqa(1, 1, 3); // Save 'mydata' into 'mydata.dat' file call saved(mydata, "mydata.dat", "x"); // Set a random seed rndseed 855; // Open handle to 'mydata.dat' which will allow // reading, writing and appending f1 = dataOpen("mydata.dat", "append"); // Create an appended dataset 'x' x = rndu(3, 1); // Write new rows to 'mydata.dat' y = writer(f1, x); // Close file handle f1 = close(f1); // Load all rows from the dataset data_new = loadd("mydata.dat"); print "mydata = " mydata; print "x = " x; print "data_new = " data_new;
After running above code,
mydata = 1.0000000 2.0000000 3.0000000 x = 0.33589398 0.62804541 0.017829664 data_new = 1.0000000 2.0000000 3.0000000 0.33589398 0.62804541 0.017829664
handle is the scalar file handle created when the file was opened. It will contain an integer which can be used to refer to the file.
close will close the file specified by handle, and will return a 0 if successful and a -1 if not successful. The handle itself is not affected by close unless the return value of close is assigned to it.
If f1 is a file handle and it contains the value 7, then after:
the file will be closed but f1 will still have the value 7. The best procedure is to do the following:
f1 = close(f1);
This will set f1 to 0 upon a successful close.
It is important to set unused file handles to zero because both open and create check the value that is in a file handle before they proceed with the process of opening a file. During open or create, if the value that is in the file handle matches that of an already open file, the process will be aborted and a File already open error message will be given. This gives you some protection against opening a second file with the same handle as a currently open file. If this happened, you would no longer be able to access the first file.
An advantage of the close function is that it returns a result which can be tested to see if there were problems in closing a file. The most common reason for having a problem in closing a file is that the disk on which the file is located is no longer in the disk drive–or the handle was invalid. In both of these cases, close will return a -1.
Files are not automatically closed when a program terminates. This allows users to run a program that opens files, and then access the files from interactive mode after the program has been run. Files are automatically closed when GAUSS exits to the operating system or when a program is terminated with the end statement. stop will terminate a program but not close files.
As a rule it is good practice to make end the last statement in a program, unless further access to the open files is desired from interactive mode. You should close files as soon as you are done writing to them to protect against data loss in the case of abnormal termination of the program due to a power or equipment failure.
The danger in not closing files is that anything written to the files may be lost. The disk directory will not reflect changes in the size of a file until the file is closed and system buffers may not be flushed.