Multiple catch blocks in C++ - Step-by-Step Execution

Concept Flow - Multiple catch blocks

Try block starts

↓

Exception thrown?

No→Try block ends normally

Yes↓

Check first catch block

↓

Matches exception type?

No→Check next catch block

Yes↓

Execute catch block

↓

Continue after try-catch

The program tries code inside try. If an exception happens, it checks each catch block in order to find a matching type and runs that catch block.

Execution Sample

C++

try {
  throw 10;
} catch (int e) {
  std::cout << "Caught int: " << e;
} catch (...) {
  std::cout << "Caught unknown";
}

This code throws an int exception and catches it with the matching int catch block.

Execution Table

Step	Action	Exception Type	Catch Block Checked	Match?	Output
1	Enter try block	None	None	N/A
2	Throw exception	int (10)	First catch (int e)	Yes	Caught int: 10
3	Catch block executed	int (10)	First catch (int e)	Yes	Caught int: 10
4	Skip other catch blocks	int (10)	Second catch (...)	No
5	Continue after try-catch	None	None	N/A

💡 Exception matched first catch block (int), so no further catch blocks checked.

Variable Tracker

Variable	Start	After throw	After catch	Final
e	undefined	10 (thrown)	10 (caught)	10 (caught)

Key Moments - 2 Insights

Why does the first catch block run and not the second?

Because the thrown exception is an int, it matches the first catch block's type int (see execution_table step 2). The second catch block is for any type (...), but it is skipped once a match is found.

What happens if no catch block matches the exception?

If no catch block matches, the exception is not handled here and will propagate up. In the table, if no 'Match?' is Yes, the program would terminate or look for another handler.

Visual Quiz - 3 Questions

Look at the execution table, which catch block handles the exception at step 2?

A First catch block (int e)

B Second catch block (...)

C No catch block handles it

D Both catch blocks handle it

💡 Hint

Check the 'Catch Block Checked' and 'Match?' columns at step 2 in the execution_table.

At which step does the program continue after handling the exception?

A Step 4

B Step 5

C Step 3

D Step 2

💡 Hint

Look for the step labeled 'Continue after try-catch' in the execution_table.

If the thrown exception was a string instead of int, which catch block would handle it?

A First catch block (int e)

B No catch block

C Second catch block (...)

D Both catch blocks

💡 Hint

The first catch only matches int, the second catch (...) matches any type (see concept_flow).

Concept Snapshot

try {
  // code that may throw
} catch (Type1 e) {
  // handle Type1 exceptions
} catch (Type2 e) {
  // handle Type2 exceptions
} catch (...) {
  // handle any exception
}

- Multiple catch blocks checked in order
- First matching catch runs
- Others skipped after match

Full Transcript

In C++, you can use multiple catch blocks after a try block to handle different types of exceptions. When an exception is thrown inside the try block, the program checks each catch block in order to find one whose type matches the thrown exception. The first matching catch block runs, and the others are skipped. If no catch block matches, the exception propagates further. This example throws an int exception and catches it with the first catch block that handles int. The second catch block with ... is a catch-all but is not reached here. Variables like the exception object 'e' get assigned the thrown value when caught. This flow helps handle different errors differently in your program.