Exception handling flow in C++ - Step-by-Step Execution

Concept Flow - Exception handling flow

Start

↓

Try block begins

↓

Code executes

↓

Exception thrown?

No→Try block ends normally

Yes↓

Catch block matches exception?

No→Unhandled exception, program terminates

Yes↓

Catch block executes

↓

Continue after catch

↓

End

The program runs code inside try. If an exception happens, it looks for a matching catch. If found, catch runs; otherwise, program stops.

Execution Sample

C++

try {
  int x = 5;
  if (x == 5) throw std::runtime_error("Error");
} catch (const std::exception& e) {
  std::cout << e.what();
}

This code throws an exception when x is 5 and catches it to print the error message.

Execution Table

Step	Action	Evaluation	Result
1	Enter try block	No exception yet	Proceed
2	Set x = 5	x = 5	x assigned
3	Check if x == 5	True	Condition met
4	Throw std::runtime_error	Exception thrown	Jump to catch
5	Catch block matches std::exception?	Yes	Catch executes
6	Print e.what()	"Error"	Output: Error
7	Exit catch block	No more code in try-catch	Program continues

💡 Exception caught and handled, normal program flow resumes

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 6	Final
x	undefined	5	5	5	5	5
exception	none	none	none	runtime_error thrown	caught with message 'Error'	caught

Key Moments - 3 Insights

Why does the program jump from the throw statement directly to the catch block?

When an exception is thrown (Step 4), normal code stops and control jumps to the matching catch block (Step 5), skipping remaining try code.

What happens if no catch block matches the thrown exception?

If no catch matches (not shown in table), the program terminates with an unhandled exception error.

Does the code after the throw inside try run?

No, after throw (Step 4), the try block stops immediately and control moves to catch.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of x after Step 3?

A 0

B undefined

C 5

D Exception object

💡 Hint

Check variable_tracker row for x at After Step 3 column

At which step does the exception get caught?

A Step 4

B Step 5

C Step 6

D Step 7

💡 Hint

Look at execution_table row where catch block matches exception

If the throw statement was removed, what would happen to the execution flow?

A Try block would finish normally, catch skipped

B Program would terminate with error

C Catch block would still execute

D Exception would be thrown later

💡 Hint

Refer to execution_table Step 4 and Step 5 for throw and catch relation

Concept Snapshot

try {
  // code that might throw
} catch (ExceptionType& e) {
  // handle exception
}

- Code in try runs normally
- If exception thrown, jump to matching catch
- If no catch matches, program ends
- After catch, program continues normally

Full Transcript

This visual trace shows how exception handling works in C++. The program starts by entering the try block and executing code. When the condition to throw an exception is met, the throw statement stops normal execution and jumps to the catch block that matches the exception type. The catch block runs and handles the error, for example by printing a message. After the catch block finishes, the program continues normally. If no catch block matches the exception, the program would terminate with an error. Variables like x keep their values through the process, but code after throw inside try does not run. This flow helps keep programs safe from unexpected errors by catching and managing exceptions.