Try–catch block in C++

Introduction

A try-catch block helps your program handle errors without crashing. It lets you try some code and catch problems if they happen.

When reading a file that might not exist.

When dividing numbers and the divisor could be zero.

When converting user input to a number that might be invalid.

When working with network connections that can fail.

Syntax

C++

try {
    // code that might cause an error
} catch (const ExceptionType& e) {
    // code to handle the error
}

The try block contains code that might cause an error.

The catch block handles the error if it happens.

Examples

This tries to convert an invalid string to an integer and catches the error to print a message.

C++

try {
    int x = std::stoi("abc");
} catch (const std::exception& e) {
    std::cout << "Error: " << e.what() << std::endl;
}

This throws a custom error and catches it to show the message.

C++

try {
    throw std::runtime_error("Oops!");
} catch (const std::runtime_error& e) {
    std::cout << "Caught: " << e.what() << std::endl;
}

Sample Program

This program tries to divide 5 by 0. It throws an error and catches it to print a friendly message instead of crashing.

C++

#include <iostream>
#include <stdexcept>

int main() {
    try {
        int a = 5;
        int b = 0;
        if (b == 0) {
            throw std::runtime_error("Cannot divide by zero");
        }
        int c = a / b;
        std::cout << "Result: " << c << std::endl;
    } catch (const std::runtime_error& e) {
        std::cout << "Error caught: " << e.what() << std::endl;
    }
    return 0;
}

Important Notes

Always catch exceptions by reference to avoid slicing.

You can have multiple catch blocks for different error types.

If no catch matches, the program will terminate.

Summary

Try-catch blocks help handle errors safely.

Put risky code inside try and handle errors in catch.

This keeps your program running smoothly even when problems happen.

Practice

1.

What is the main purpose of a try-catch block in C++?

easy

A. To handle errors and exceptions safely during program execution

B. To speed up the program by skipping code

C. To declare variables globally

D. To create loops that run multiple times

Solution

1. Step 1: Understand the role of try block

   The try block contains code that might cause an error or exception.

2. Step 2: Understand the role of catch block

   The catch block handles the error so the program does not crash.

3. Final Answer:

   To handle errors and exceptions safely during program execution -> Option A

4. Quick Check:

   Try-catch handles errors = B [OK]

Hint: Try-catch blocks catch errors to keep programs running [OK]

Common Mistakes:

• Thinking try-catch speeds up code
• Confusing try-catch with loops
• Using try-catch to declare variables

2.

Which of the following is the correct syntax to start a try block in C++?

?

easy

A. catch {

B. try (

C. try:

D. try {

Solution

1. Step 1: Recall try block syntax

   The try block starts with the keyword try followed by curly braces { }.

2. Step 2: Identify correct option

   Only try { uses try { which is correct syntax to start the block.

3. Final Answer:

   try { -> Option D

4. Quick Check:

   Try block starts with try { = C [OK]

Hint: Try block always starts with 'try {' in C++ [OK]

Common Mistakes:

• Using parentheses instead of curly braces
• Starting with catch instead of try
• Using colon after try

3.

What will be the output of the following C++ code?

try {
    int x = 5 / 0;
    std::cout << "Result: " << x << std::endl;
} catch (const std::exception& e) {
    std::cout << "Caught exception" << std::endl;
}

medium

A. Result: 0

B. Caught exception

C. Program crashes with division by zero error

D. No output

Solution

1. Step 1: Analyze division by zero in C++

   Integer division by zero causes undefined behavior and usually crashes the program; it does not throw a standard exception.

2. Step 2: Check catch block type

   The catch block catches std::exception types, but division by zero does not throw this exception automatically.

3. Final Answer:

   Program crashes with division by zero error -> Option C

4. Quick Check:

   Integer division by zero crashes = D [OK]

Hint: Division by zero crashes, not caught by std::exception [OK]

Common Mistakes:

• Assuming catch block catches all errors
• Expecting output 'Caught exception'
• Thinking division by zero returns zero

4.

Identify the error in this C++ code snippet:

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

medium

A. The catch block for int should come after catch(...)

B. No error; code is correct

C. Multiple catch blocks are not allowed

D. Throwing int is invalid

Solution

1. Step 1: Check throw and catch types

   The code throws an int and catches it with catch(int e), which matches correctly.

2. Step 2: Verify catch block order

   The specific catch catch(int e) comes before the catch-all catch(...), which is correct.

3. Final Answer:

   No error; code is correct -> Option B

4. Quick Check:

   Throw int caught by int catch first = A [OK]

Hint: Specific catch blocks must come before catch(...) [OK]

Common Mistakes:

• Placing catch(...) before specific catch
• Thinking multiple catch blocks are invalid
• Believing throwing int is not allowed

5.

Consider this code snippet:

try {
    std::string s = "hello";
    int n = std::stoi(s);
    std::cout << n << std::endl;
} catch (const std::invalid_argument& e) {
    std::cout << "Invalid argument caught" << std::endl;
} catch (...) {
    std::cout << "Other exception caught" << std::endl;
}

What will be the output and why?

hard

A. Invalid argument caught

B. Other exception caught

C. hello

D. Program crashes

Solution

1. Step 1: Understand std::stoi behavior

   Trying to convert "hello" to int using std::stoi throws std::invalid_argument exception because "hello" is not a number.

2. Step 2: Check catch blocks

   The first catch block catches std::invalid_argument exceptions and prints "Invalid argument caught".

3. Final Answer:

   Invalid argument caught -> Option A

4. Quick Check:

   std::stoi throws invalid_argument for non-numeric string = A [OK]

Hint: std::stoi throws invalid_argument on bad input [OK]

Common Mistakes:

• Expecting program to print 'hello'
• Assuming catch(...) runs instead of specific catch
• Thinking program crashes without catch