What is the advantage of using try {} catch {} versus if {} else {}

Question

I am switching from plain mysql in php to PDO and I have noticed that the common way to test for errors is using a try / catch combination instead of if / else combinations.

Answer 1

Throwing and catching an exception is an expensive operation compared with most any other primitive operation. If this is a piece of code that needs to perform well (eg, in a tight loop), you will want to look at your use case - if you expect the exceptions to be thrown relatively often, you will be better off with an if/else perforance-wise (unless the underlying code is just wrapping an exception for you, in which case there's no gain at all). If the exceptions are only thrown in rare circumstances, then you're better off with a try/catch to avoid the overhead of branching in a tight loop.

Answer 2

Since PDO is using objects, they are raising Exceptions if an error occur. The old mysql/mysqli were mere functions and didn't throw Exceptions they simply returned error codes. Try/catch is used when an Exception can be thrown from the code, and you catch it in the catch-clause, which is an object oriented way to handle errors. You can't catch Exceptions with if/else blocks - they share nothing with try/catch.

Answer 3

In general, try-catch blocks are great because they will break (move to the catch statement) whenever the exception occurs. If-else blocks rely on you predicting when the error will happen.

Edit: Also, catch blocks won't stop your code from halting when an error is hit.

Answer 4

TRY/ CATCH can be used within the programming context where you have very little information about the error or you think that might can occur such as.

#include <iostream>
using namespace std;

int main (){
    try{
        while(true){
            new int[100000];
        }
    }
    catch(bad_alloc& e){
       cout << e.what() << endl;
     }
 }

Although there are no semantic or compile-time errors in the program, but it's understandable that it posses a run-time error which is "bad_alloc" which appears when you try to continuously allocate the memory and your program run out of memory. This exception is defined in bad_alloc standard class which is a child-class of class "Exception", since it throws an implicit exception, throw keyword is not implied here.

You can also use try/catch to check if the file is accidentally deleted and can use if/else to check if there exists a file or not, both have their own advantages.

Answer 5

That’s exactly the advantage, using one try/catch instead of multiple if statements. You will also be able to catch any unanticipated errors.

Answer 6

Try and Catch functions are useful whenever there is a communication between functions. In Try and Catch , if there exists an exception in the TRY block, the control is transferred directly to the CATCH block which would store our exception condition. This however is not possible in case of IF ELSE, where in IF condition , if there exists an exception, the control cannot go to the ELSE block howsoever in any case.

int division(int a,int b){
    if(b==0)
       throw 101;
    return a/b;
}

int main()
{
    int a=10,b=0,c;
    try{
        c=division(a,b);
        cout<<c<<endl;
    }
    catch(int a){
        cout<<"Division not possible by 0"<<endl;
   }
}

Consider the following Code: throw and catch function is used for communication between functions division and the main function. Note that the statement to print c is not executed when b is 0 as the control directly transfers to the catch block after the value os thrown. This however would not have been possible , had it been IF ELSE here.