C++ Exception Handling Mechanisms

In this article, we will delve into C++ exception handling mechanisms with examples, as well as explore topics like static_assert, assert, try-catch usage, function try-catch, and exception handling in constructor initializer lists.

C++ Exception Handling and Error Control Mechanisms

In C++ programming, there are several mechanisms to handle error situations and ensure the proper functioning of the program. These mechanisms are used to detect, handle, and take necessary actions for errors at either compile time or runtime. In this article, we will provide a detailed examination of C++ exception handling mechanisms and other error control methods.

C++ Exception Handling Mechanisms

try-catch Blocks

C++ exception handling is achieved through try-catch blocks. The try block contains a code snippet where a potential error might occur. If an error occurs, the code inside the catch block runs. The catch block matches the thrown exception type and performs the relevant actions.

try {
    // Code snippet where an error might occur
} catch (ExceptionType1 e) {
    // Code to run in case of an ExceptionType1 error
} catch (ExceptionType2 e) {
    // Code to run in case of an ExceptionType2 error
} catch (...) {
    // Code to run in case of all other errors
}

When an error is thrown within the try block, the catch blocks are checked in order, and the matching catch block is executed. If no catch block matches, the program terminates, and an error message is displayed.

throw Statement

The throw statement is used to determine error conditions and throw an exception. When an exception is thrown, the program flow transfers to the relevant catch block.

throw ExceptionType(argument);

The throw statement is used with a specific exception type and necessary arguments. The thrown exception follows the stack structure of the program until it is caught by the appropriate catch block.

catch(…) Block

The catch(...) block is used to catch exceptions of any type. However, specific information about the caught exceptions is not accessible within this block. This type of catch block is typically used to handle unexpected error situations.

try {
    // Code snippet where an error might occur
} catch (...) {
    // Code to run in case of any type of exception
}

std::exception Class

The std::exception class is a fundamental exception class found in the C++ Standard Library. Other exception classes are derived from this class and are often used to hold information about error conditions. The std::exception class provides a function called what() that is overridden by derived classes.

#include <exception>

class MyException : public std::exception {
public:
    const char* what() const noexcept {
        return "This is a custom exception.";
    }
};

Compile-Time Error Control

static_assert

static_assert is a compile-time control mechanism introduced with C++11. It is used to check whether a specific condition is true at compile time. If the condition is true, the compilation process continues as usual. However, if the condition is false, the compiler reports an error and prevents the program from being compiled.

static_assert(sizeof(int) == 4, "The size of an int should be 4 bytes!");

The static_assert statement expects the condition to be true. If the condition is false, the compiler reports an error and displays the specified message. This mechanism is useful for checking the validity of certain conditions during the compilation process.

Runtime Error Control

assert

assert is a runtime control mechanism used to check error conditions in C++ programs. The assert statement verifies whether a condition is true. If the condition is true, the program continues to run normally. However, if the condition is false, an assertion failure occurs, and the program execution is halted.

#include <cassert>

int main() {
    int x = 5;
    int y = 10;

    assert(x == y); // The program stops here if x and y are not equal.

    return 0;
}

The assert statement is used in places where the programmer expects a specific condition to always be true. If the condition is false, the assert statement halts the program’s execution with an error message. This mechanism is used to ensure that the program runs correctly.

Use Cases

try-catch Blocks

try-catch blocks are the most common way to handle error situations. They are used in the following cases:

try-catch blocks are used to handle errors that may occur during the execution of specific code snippets within a function. For example, we can use them to handle errors during file read or write operations.
try-catch blocks can be used to check error conditions inside a class’s constructor or destructor functions. In particular, handling errors during the initialization or cleanup of a class’s data members is essential.
Error conditions in template functions can be handled using try-catch blocks. For example, we can use try-catch blocks to handle error situations within a template function where an algorithm is running.

Function try-catch

Function try-catch is a try-catch mechanism applied to functions or a class’s member functions. This structure is used inside the constructor or destructor functions of a class. If the relevant function fails, the operations inside the catch block are performed. For example:

class MyClass {
public:
    MyClass() try {
        // Code snippet where an error might occur
    } catch (ExceptionType e) {
        // Code to run in case of an error
    }

    ~MyClass() try {
        // Code snippet where an error might occur
    } catch (ExceptionType e) {
        // Code to run in case of an error
    }
};

This structure provides protection against error situations in the constructor or destructor functions of a class.

Function-Try blocks can also be used inside regular functions. For example:

int f(int n = 2) try
{
    ++n; // increments the function parameter
    throw n;
}
catch(...)
{
    ++n; // n is in scope and still refers to the function parameter
    assert(n == 4);
    return n;
}

As seen in the example above, the scope of the “n” object has been extended, and it can be accessed from the catch block.

Exception Handling in Constructor Initializer List

To catch exceptions in the constructor initializer list, try-catch blocks are used within the expressions that initialize the relevant data members. This way, you can handle error conditions for each data member initialization expression separately. For example:

class MyClass {
public:
    MyClass() 
		try : member1(), member2() {
    	// Code snippet where an error might occur during the initialization of member1 or member2
    }
		catch(const std::exception & e)
		{
			std::cout << e.what() << '\n';
		}
    
private:
    int member1;
    int member2;
};

This structure is used to handle errors that may occur during the initialization of a class’s data members

Summary

In this article, we examined C++ exception handling mechanisms and error control methods in detail. Mechanisms such as try-catch blocks, the throw statement, catch(...) blocks, and the std::exception class are used to detect error conditions and perform the necessary actions. Additionally, compile-time and runtime error control mechanisms like static_assert and assert are used to ensure the correct operation of the program.

Handling error situations correctly and ensuring the safety and error-free operation of the program is essential. By using these mechanisms, you can control error situations in C++ programs, perform appropriate actions, and create a robust codebase.

I hope this article has provided a more comprehensive understanding of C++ exception handling and error control mechanisms.