MATLAB Error Control Statement-try, catch

MATLAB define some functions that are used to control error. The try-catch statement is an error control function, which is explained below.

Try – catch statement

Try-catch statement provides error handling control. General form of the try-catch statement is

Syntax:

try  
    Statements  
catch   exception  
    Statements  
end  

Statements between try and catch execute first. If no error appears in executing statements between try and catch, MATLAB further executes the statements/code after the end keyword. If an error occurs during the execution of statements between try and catch, MATLAB executes statements between catch and end. Try-catch statement can be explained with the help of the following example.

Example:

a = ones(4);  
b = zeros(3);  
try  
    c = [a;b];  
catch ME  
    disp(ME)  
end  

Output:

MException with properties:

    identifier: 'MATLAB:catenate:dimensionMismatch'
       message: 'Dimensions of arrays being concatenated are not consistent.'
         cause: {0×1 cell}
         stack: [3×1 struct]
    Correction: []

Following are the points while using a try/catch statement in MATLAB:

• The control of the program execution first enters the try block and executes each statement.
• If any error occurs during the execution, then the control immediately passes to the catch block, leaving any other statements of the try block unexecuted.
• If there is no error occurs inside try block, then the control doesn’t enter the catch block. The control then reaches to the statements after the end keyword of try/ catch block.
• Whenever any error or exception occurs in the try block, the MATLAB constructs an instance of the MException class and returns the object in the catch statement.
• The MException class object can be accessed with the variable ME.
• The MException class object has five properties-identifier, message, stack, cause, and Correction. These properties describe details about the occurred exception.
• We can’t use multiple catch block, only one catch block within a try block is allowed.
• We can use nested try/catch blocks if required.

Example showing MException class object properties:

a = ones(4);  
b = zeros(3);  
try  
    c = [a;b];  
catch ME  
   % strcmp string compare function, to check the same string in ME identifier  
    if (strcmp(ME.identifier,'MATLAB:catenate:dimensionMismatch'))  
    % if it is true then change the message property  
        msg = ['dimension mismatch occured: First argument has ',...  
            num2str(size(a,2)), ' columns, while second argument has ',...  
            num2str(size(b,2)),' columns.'];  
        causeException = MException('MATLAB:mycode:dimensions',msg)  
        ME = addCause(ME, causeException);  
    end  
   
end  

Output:

causeException = 
  MException with properties:

    identifier: 'MATLAB:mycode:dimensions'
       message: 'dimension mismatch occured: First argument has 4 columns, while second argument has 3 columns.'
         cause: {}
         stack: [0×1 struct]
    Correction: []

Program Termination

Program termination control allows to exit from our program at some point before its normal termination point.