What is logic_error in C++: Explanation and Example

logic_error in C++ is a standard exception type used to signal errors in the program's logic, such as invalid arguments or broken assumptions. It is part of the std::exception family and helps catch mistakes that can be detected before the program runs incorrectly.

How It Works

Imagine you are following a recipe to bake a cake. If you add salt instead of sugar, the cake won't taste right because the instructions were not followed correctly. In programming, logic_error is like a warning that the recipe (your program's logic) has a mistake.

When your program detects a situation that should never happen if the logic is correct, it can throw a logic_error. This exception tells the program to stop normal execution and handle the problem, preventing further errors or incorrect results.

It is part of C++'s standard library exceptions and is used to catch errors that come from wrong assumptions or invalid operations in the code, such as passing a wrong value to a function or violating a rule your program depends on.

Example

This example shows how to throw and catch a logic_error when a function receives an invalid argument.

cpp

#include <iostream>
#include <stdexcept>

void checkAge(int age) {
    if (age < 0 || age > 150) {
        throw std::logic_error("Age must be between 0 and 150.");
    }
    std::cout << "Age is valid: " << age << std::endl;
}

int main() {
    try {
        checkAge(25);  // valid age
        checkAge(-5);  // invalid age, will throw
    } catch (const std::logic_error& e) {
        std::cout << "Logic error caught: " << e.what() << std::endl;
    }
    return 0;
}

Output

Age is valid: 25
Logic error caught: Age must be between 0 and 150.

When to Use

Use logic_error when your program detects a problem caused by incorrect logic or invalid input that breaks your program's rules. For example:

• Checking function arguments for invalid values.
• Detecting impossible states in your program.
• Signaling that a precondition or assumption was violated.

This helps you find bugs early and handle them gracefully instead of letting the program continue with wrong data.

Key Points

• logic_error is a standard exception for logic mistakes in code.
• It inherits from std::exception and can be caught using standard exception handling.
• Throw it when your program detects invalid arguments or broken assumptions.
• Helps improve program reliability by catching bugs early.

Key Takeaways

logic_error signals errors caused by incorrect program logic or invalid input.

It is part of C++ standard exceptions and inherits from std::exception.

Throw logic_error to catch broken assumptions or invalid arguments.

Catching logic_error helps prevent bugs and unexpected behavior.

Use it to make your program safer and easier to debug.