C++ Errors

❌ C++ Errors

Errors in C++ are problems in a program that prevent it from compiling correctly or behaving as expected at runtime.
Understanding errors helps you debug faster and write reliable programs.

🔹 1. Types of Errors in C++

C++ errors are mainly classified into three types:

  1. Compile-Time Errors

  2. Run-Time Errors

  3. Logical Errors

🔹 2. Compile-Time Errors

These errors are detected by the compiler before the program runs.

🔸 Common Causes

  • Syntax mistakes

  • Missing semicolon

  • Undeclared variables

  • Type mismatch

Example

#include <iostream>
using namespace std;int main() {
int x = 10
cout << x;
}

❌ Error: missing ;

✔ Fix:

int x = 10;

Example: Undeclared Variable

cout << y; // y not declared

🔹 3. Run-Time Errors

These errors occur while the program is running and may cause the program to crash.

🔸 Common Causes

  • Division by zero

  • Accessing invalid memory

  • Dereferencing nullptr

  • File not found

Example: Division by Zero

int a = 10, b = 0;
cout << a / b; // ❌ runtime error

Example: Null Pointer

int *p = nullptr;
cout << *p; // ❌ runtime error

🔹 4. Logical Errors

The program runs successfully, but produces incorrect output.

Example

int a = 10, b = 5;
cout << a - b; // expected sum but subtraction used

✔ Hardest errors to find
✔ Require careful testing and logic checking

🔹 5. Linker Errors

Occur when the linker cannot find function definitions.

Example

void show(); // declared but not defined

int main() {
show();
}

❌ Linker error: undefined reference to show()

🔹 6. Runtime Error Handling (Exceptions)

C++ uses exception handling to manage runtime errors.

try {
int a = 10, b = 0;
if (b == 0)
throw "Division by zero";
cout << a / b;
}
catch (const char* msg) {
cout << msg;
}

🔹 7. Common C++ Error Messages

Error MessageMeaning
expected ';'Missing semicolon
undeclared identifierVariable not declared
segmentation faultInvalid memory access
undefined referenceMissing function definition

🔹 8. Debugging Tips

  • Read error messages carefully

  • Fix first error first

  • Use cout to trace values

  • Use debugger (gdb / IDE debugger)

  • Enable warnings:

g++ -Wall program.cpp

🔹 9. Preventing Errors (Best Practices)

  • Initialize variables

  • Avoid global variables

  • Use const and references

  • Check pointers before use

  • Handle file open errors

  • Use modern C++ features (smart pointers)

🔁 Errors vs Warnings

ErrorsWarnings
Stop compilationCompilation continues
Must fixShould fix
CriticalPotential issues

📌 Summary

  • Compile-time errors → syntax & type issues

  • Run-time errors → occur during execution

  • Logical errors → wrong output

  • Linker errors → missing definitions

  • Proper debugging reduces errors

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