Opening and Closing a File:

The Files are opened with the fopen function. By the default, fopen function opens a file for reading. If the other mode is preferred, a permission string is used to identify which mode (example, writing or appending). The fopen function returns 1 when it is not successful in opening a file, or an integer value, that becomes the file identifier when it is successful. The file identifier is then used to refer the file whenever calling other file I/O functions. The common form is as shown below:

fid = fopen('filename', 'permission string');

The permission strings include:

r reading (this is the default)

w writing

a appending

View helps fopen for others.

Afterward the fopen is tried; the value returned must be tested to make sure that the file was efficiently opened. For illustration, if the files do not exist, the fopen will not be successful. As the fopen function returns -1 when the file was not found, this can be checked to decide whether to print an error message or to continue and use the file. For illustration, if it is preferred to read from a file 'samp.

dat':

fid = fopen('samp.dat');

if fid == -1

   disp('File open not successful')

else

   % Carry on and use the file!

end

The Files must be closed whenever the program has finished the reading from or writing to them. The function which accomplishes this is the fclose function, that returns 0 if the file close was successful, or -1 if not. The Individual files can be closed by identifying the file identifier, or if more than one file is open, then all the open files can be closed by passing the string 'all' to the fclose function. The common forms are as shown below:

closeresult = fclose(fid);

closeresult = fclose('all');

This must also be checked with an if-else statement to make sure that it was successful.