TRY-CATCH Try and Catch Statement

Section: Flow Control

Usage

The try and catch statements are used for error handling and control. A concept present in C++, the try and catch statements are used with two statement blocks as follows 
   try
     statements_1
   catch
     statements_2
   end

The meaning of this construction is: try to execute statements_1, and if any errors occur during the execution, then execute the code in statements_2. An error can either be a FreeMat generated error (such as a syntax error in the use of a built in function), or an error raised with the error command.

Examples

Here is an example of a function that uses error control via try and catch to check for failures in fopen. 

     read_file.m
function c = read_file(filename)
try
   fp = fopen(filename,'r');
   c = fgetline(fp);
   fclose(fp);
catch
   c = ['could not open file because of error :' lasterr]
end

Now we try it on an example file - first one that does not exist, and then on one that we create (so that we know it exists). 

--> read_file('this_filename_is_invalid')

c = 
could not open file because of error :Access mode r requires file to exist 

ans = 
could not open file because of error :Access mode r requires file to exist 
--> fp = fopen('test_text.txt','w');
--> fprintf(fp,'a line of text\n');
--> fclose(fp);
--> read_file('test_text.txt')

ans = 
a line of text