Multiple catch blocks in C++

Introduction

Multiple catch blocks let you handle different kinds of errors separately. This helps your program respond correctly to each problem.

When you want to handle different error types in different ways.

When your code might throw different exceptions and you want clear responses.

When you want to keep your error handling organized and easy to read.

Syntax

C++

try {
    // code that might throw an exception
} catch (const ExceptionType1& e1) {
    // handle ExceptionType1
} catch (const ExceptionType2& e2) {
    // handle ExceptionType2
} catch (...) {
    // handle any other exceptions
}

The try block contains code that might cause an error.

Each catch block handles a specific type of error.

Examples

This example catches standard exceptions and any other unknown exceptions.

C++

try {
    int a = 10, b = 0;
    if (b == 0) throw std::runtime_error("Division by zero");
} catch (const std::exception& e) {
    std::cout << "Standard exception: " << e.what() << std::endl;
} catch (...) {
    std::cout << "Unknown exception caught" << std::endl;
}

This example shows catching exceptions of different types: int and double.

C++

try {
    throw 20;
} catch (int e) {
    std::cout << "Caught an int exception: " << e << std::endl;
} catch (double e) {
    std::cout << "Caught a double exception: " << e << std::endl;
}

Sample Program

This program throws a runtime error and catches it with the matching catch block, printing the error message.

C++

#include <iostream>
#include <string>
#include <stdexcept>

int main() {
    try {
        std::string input = "error";
        if (input == "error") {
            throw std::runtime_error("Runtime error occurred");
        } else if (input == "fail") {
            throw std::logic_error("Logic error occurred");
        }
    } catch (const std::runtime_error& e) {
        std::cout << "Caught runtime error: " << e.what() << std::endl;
    } catch (const std::logic_error& e) {
        std::cout << "Caught logic error: " << e.what() << std::endl;
    } catch (...) {
        std::cout << "Caught unknown exception" << std::endl;
    }
    return 0;
}

Important Notes

Catch blocks are checked in order. The first matching catch block runs.

The catch(...) block catches any exception not caught by earlier blocks.

Use specific exception types first, then more general ones.

Summary

Multiple catch blocks let you handle different errors separately.

Put the try block around code that might fail.

Use catch blocks for each error type you want to handle.

Practice

1.

What is the main purpose of using multiple catch blocks in C++?

easy

A. To speed up the program execution

B. To handle different types of exceptions separately

C. To avoid using try blocks

D. To declare multiple variables at once

Solution

1. Step 1: Understand the role of catch blocks

   Catch blocks are used to handle exceptions that occur in the try block.

2. Step 2: Recognize the benefit of multiple catch blocks

   Multiple catch blocks allow handling different exception types separately, so each error can be managed properly.

3. Final Answer:

   To handle different types of exceptions separately -> Option B

4. Quick Check:

   Multiple catch blocks = handle different exceptions [OK]

Hint: Multiple catch blocks handle different errors separately [OK]

Common Mistakes:

• Thinking multiple catch blocks speed up code
• Confusing catch blocks with variable declarations
• Believing try blocks are not needed with multiple catch blocks

2.

Which of the following is the correct syntax to catch any remaining exceptions in multiple catch blocks in C++?

try {
    // code
}
catch (int e) {
    // handle int
}
_____ {
    // handle other
}

easy

A. catch (...)

B. catch (string e)

C. catch (double e)

D. catch (char e)

Solution

1. Step 1: Identify the syntax for catch-all block

   The catch(...) block catches any exception type not caught by previous catch blocks.

2. Step 2: Confirm correct syntax

   Only catch(...) uses ellipsis and no variable type, making it the correct syntax for a generic catch block.

3. Final Answer:

   catch (...) -> Option A

4. Quick Check:

   catch(...) = catch all exceptions [OK]

Hint: Use catch(...) to catch all exceptions generically [OK]

Common Mistakes:

• Using catch without parentheses
• Trying to catch unknown types without ellipsis
• Misplacing catch blocks after try

3.

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

try {
    throw 10;
}
catch (double e) {
    std::cout << "Double exception";
}
catch (int e) {
    std::cout << "Integer exception: " << e;
}

medium

A. Compilation error

B. Double exception

C. No output

D. Integer exception: 10

Solution

1. Step 1: Identify the thrown exception type

   The code throws an integer exception with value 10.

2. Step 2: Match thrown exception with catch blocks

   The first catch block expects a double, so it is skipped. The second catch block matches int, so it executes and prints the message.

3. Final Answer:

   Integer exception: 10 -> Option D

4. Quick Check:

   throw int = catch int block runs [OK]

Hint: Match thrown type with catch parameter type [OK]

Common Mistakes:

• Assuming first catch always runs
• Confusing int and double types
• Expecting no output if types differ

4.

Find the error in this code snippet using multiple catch blocks:

try {
    throw "error";
}
catch (int e) {
    std::cout << "Int error";
}
catch (char e) {
    std::cout << "Char error";
}

medium

A. Missing catch block for const char* exception

B. Try block syntax is incorrect

C. Cannot throw string literals

D. Catch blocks must be in reverse order

Solution

1. Step 1: Identify the thrown exception type

   The code throws a string literal, which is of type const char*.

2. Step 2: Check catch blocks for matching types

   Catch blocks handle int and char, but not const char*. So no catch block matches the thrown exception, causing an unhandled exception.

3. Final Answer:

   Missing catch block for const char* exception -> Option A

4. Quick Check:

   Thrown type must match catch parameter [OK]

Hint: Catch blocks must match thrown exception types exactly [OK]

Common Mistakes:

• Assuming char catch handles string literals
• Thinking try block syntax is wrong
• Believing catch order matters for unrelated types

5.

Consider this code with multiple catch blocks:

try {
    throw std::runtime_error("runtime error");
}
catch (std::exception& e) {
    std::cout << "Exception: " << e.what();
}
catch (std::runtime_error& e) {
    std::cout << "Runtime error: " << e.what();
}

What will be the output and why?

hard

A. Exception: runtime error

B. Runtime error: runtime error

C. Compilation error due to catch order

D. No output because exception is not caught

Solution

1. Step 1: Understand exception inheritance

   std::runtime_error is derived from std::exception, so it matches both catch blocks.

2. Step 2: Analyze catch block order

   The first catch block catches std::exception by reference, so it catches the thrown runtime_error before the second catch block is reached.

3. Step 3: Determine output

   The first catch block prints "Exception: runtime error" using e.what().

4. Final Answer:

   Compilation error due to catch order -> Option C

5. Quick Check:

   Derived class catch must come before base class catch to avoid compilation error [OK]

Hint: Catch derived exceptions before base to avoid compilation error [OK]

Common Mistakes:

• Expecting derived catch to run first
• Thinking catch order causes no compilation error
• Assuming no output if multiple matches