if statement for error

Hi, is it possible to use an if-statement that responds wether an error occurs while running a script? and if the answer is yes, how can one achieve this?

here is a simple idea of what I mean

if error occurs
   *do something*
end

Answer 1

[John D'Errico]

No. You cannot use if to find an error, because an error interrupts and stops execution of your code. However, you can use a try block to do that. Try intercepts any error that occur inside the try block, and immediately transfers execution into the catch block, where you can do as you wish.

try
  a = 1:2;
  a(5)
catch
  disp('you did something wrong')
end

you did something wrong

So, when the try block executed, it assigned a to a vector of length 2. I can verify that a exists, and is of length 2.

a
a =
    1     2

But then I did something silly, that will result in an error. Instead of allowing the error to be generated, it traps into the catch block, where I could have done whatever I wanted to, with the code continuing execution there.

No error message was generated. So, while I would have expected to see this:

a(5)
Index exceeds array bounds.

Instead, it dropped into the catch block. We can extract that error message, if we want to do so though.

lasterror
ans = 
  struct with fields:

       message: 'Index exceeds array bounds.'
    identifier: 'MATLAB:badsubscript'
         stack: [0×1 struct]

So, you cannot use if. But you CAN use try/catch.

[Thijs Obers]

so if I understand this correctly, try-catcht is basically an if-ifelse statement for errors?

[Walter Roberson]

try/catch is basically a GOTO for errors.