In real-world systems, things often go wrong. A bank server may become unreachable, a file may not open, or a user may enter invalid data. An exception is a runtime event that interrupts the normal flow of a program. Instead of crashing, the program “throws” an exception, which gives you a chance to respond.<\/p>\n\n\n\n
Exception handling allows programmers to write applications that remain stable even if something unexpected happens.<\/p>\n\n\n\n
Imagine you withdraw money from an ATM. If the machine runs out of cash, the system does not crash. Instead, it shows a message like “Unable to process request.” This is exception handling in action.<\/p>\n\n\n\n
try<\/code> Block<\/h2>\n\n\n\nA try<\/code> block contains the code that might cause an exception.<\/p>\n\n\n\ntry {\n \/\/ risk code\n}\ncatch(...) {\n \/\/ handle risk\n}\n<\/code><\/pre>\n\n\n\nThe catch<\/code> Block<\/h2>\n\n\n\nA catch<\/code> block captures the exception. It must appear after the try<\/code> block. You can use specific type catches, reference catches or catch-all.<\/p>\n\n\n\nThe throw<\/code> Statement<\/h2>\n\n\n\nYou use throw<\/code> to manually create an exception when something unexpected occurs.<\/p>\n\n\n\nProgram 1: Division Calculator With Basic try\/catch\/throw<\/h3>\n\n\n\n#include <iostream>\nusing namespace std;\n\nint main() {\n int a, b;\n cout << \"Enter two numbers: \";\n cin >> a >> b;\n\n try {\n if (b == 0)\n throw \"Division by zero!\";\n\n cout << \"Result = \" << (a \/ b) << endl;\n }\n catch (const char* msg) {\n cout << \"Error: \" << msg << endl;\n }\n\n return 0;\n}\n<\/code><\/pre>\n\n\n\nExplanation: The program asks the user for two numbers. If the denominator is zero, we throw an exception. The catch block displays the error message without crashing the program.<\/p>\n\n\n\n
Standard C++ Exception Types<\/h1>\n\n\n\n
C++ has a built-in hierarchy of exceptions based on std::exception<\/code>. Some commonly used exception classes include std::runtime_error<\/code>, std::out_of_range<\/code>, std::invalid_argument<\/code>, and std::bad_alloc<\/code>.<\/p>\n\n\n\nUsing Standard Exceptions<\/h3>\n\n\n\n#include <iostream>\n#include <vector>\n#include <stdexcept>\nusing namespace std;\n\nint main() {\n vector<int> nums = {10, 20, 30};\n\n try {\n cout << nums.at(5);\n }\n catch (const out_of_range &e) {\n cout << \"Exception caught: \" << e.what() << endl;\n }\n\n return 0;\n}\n<\/code><\/pre>\n\n\n\nExplanation: vector.at()<\/code> throws an exception if the index is invalid. The catch block displays the standard exception message from e.what()<\/code>.<\/p>\n\n\n\nCreating Custom Exceptions<\/h1>\n\n\n\nWhy Create Custom Exceptions?<\/h2>\n\n\n\n
In bigger systems (e.g., Hospital Management, Banking Systems), domain-specific errors give clarity. Examples include LowBalanceException<\/code>, InvalidAgeException<\/code>, and FileCorruptException<\/code>.<\/p>\n\n\n\nHow to Define a Custom Exception<\/h2>\n\n\n\n
You create your own class that inherits from std::exception<\/code> and override the what()<\/code> function.<\/p>\n\n\n\nProgram 3: Custom Exception for Invalid Age<\/h3>\n\n\n\n#include <iostream>\n#include <exception>\nusing namespace std;\n\nclass InvalidAge : public exception {\npublic:\n const char* what() const noexcept override {\n return \"Age must be between 18 and 60.\";\n }\n};\n\nint main() {\n int age;\n cout << \"Enter your age: \";\n cin >> age;\n\n try {\n if (age < 18 || age > 60)\n throw InvalidAge();\n\n cout << \"Age accepted!\" << endl;\n }\n catch (const InvalidAge &e) {\n cout << \"Error: \" << e.what() << endl;\n }\n\n return 0;\n}\n<\/code><\/pre>\n\n\n\nExplanation: Custom exception gives a meaningful message. If the user enters invalid age, the program does not terminate abruptly.<\/p>\n\n\n\n
Exception Propagation and Rethrowing<\/h1>\n\n\n\n
Exceptions can move from one function to another. If a function cannot handle the error, it can simply throw it upward.<\/p>\n\n\n\n
Exception Propagation Example<\/h3>\n\n\n\n#include <iostream>\nusing namespace std;\n\nvoid level3() {\n throw \"File not found!\";\n}\n\nvoid level2() {\n level3();\n}\n\nvoid level1() {\n level2();\n}\n\nint main() {\n try {\n level1();\n }\n catch (const char* msg) {\n cout << \"Caught in main: \" << msg << endl;\n }\n\n return 0;\n}\n<\/code><\/pre>\n\n\n\nExplanation: The exception thrown in level3()<\/code> travels up through level2()<\/code> and level1()<\/code> until it is caught in main()<\/code>.<\/p>\n\n\n\nResource Management and Exception Safety<\/h1>\n\n\n\n
One of the biggest reasons to use exception handling is protecting resources such as files, database connections, network sockets, and memory. C++ uses RAII (Resource Acquisition Is Initialization) to prevent resource leaks.<\/p>\n\n\n\n
Example With File Handling<\/h2>\n\n\n\n#include <iostream>\n#include <fstream>\nusing namespace std;\n\nclass FileReader {\n ifstream file;\n\npublic:\n FileReader(const string &name) {\n file.open(name);\n if (!file)\n throw \"Unable to open file!\";\n }\n\n ~FileReader() {\n cout << \"Closing file...\" << endl;\n if (file.is_open())\n file.close();\n }\n\n void display() {\n string line;\n while (getline(file, line))\n cout << line << endl;\n }\n};\n\nint main() {\n try {\n FileReader fr(\"data.txt\");\n fr.display();\n }\n catch (const char* msg) {\n cout << \"Exception: \" << msg << endl;\n }\n\n return 0;\n}\n<\/code><\/pre>\n\n\n\nSmart Pointers and Exception Safety<\/h2>\n\n\n\n#include <iostream>\n#include <memory>\nusing namespace std;\n\nint main() {\n try {\n unique_ptr<int> ptr(new int(10));\n\n cout << \"Value: \" << *ptr << endl;\n\n throw \"Some error occurred!\";\n }\n catch (const char* msg) {\n cout << \"Caught: \" << msg << endl;\n }\n\n return 0;\n}\n<\/code><\/pre>\n\n\n\nExplanation: unique_ptr<\/code> automatically frees memory even if an exception occurs, preventing memory leaks.<\/p>\n\n\n\n<\/p>\n","protected":false},"excerpt":{"rendered":"
In real-world systems, things often go wrong. A bank server may become unreachable, a file may not open, or a user may enter invalid data. An exception is a runtime event that interrupts the normal flow of a program. Instead of crashing, the program “throws” an exception, which gives you a chance to respond. Exception handling allows programmers to write applications that remain stable even if something unexpected happens. Imagine you withdraw money from an ATM. If the machine runs…<\/p>\n