C++ Header Files

Header files in C++ contain declarations of functions, classes, constants, and macros. They allow code to be modular, reusable, and organized. You can include them in your source files using the #include directive.

1. Standard Header Files

C++ provides a rich set of standard header files in the standard library. These headers contain pre-defined classes, functions, and objects for common tasks.

Header	Purpose	Example
	Input/Output streams	cout, cin, cerr
	Mathematical functions	sqrt(), pow(), sin()
	String class and functions	std::string, getline()
	Dynamic array container	std::vector v;
	Common algorithms	sort(), find(), max_element()
	File handling	ifstream, ofstream, fstream
	Input/output formatting	setw(), setprecision()

2. Custom Header Files

You can create your own header files to store declarations and reuse them across multiple source files. Typically, custom headers have the .h extension.

              
            
C++

          Creating and including a custom header
        
// myfunctions.h
#ifndef MYFUNCTIONS_H
#define MYFUNCTIONS_H

void greet();

#endif

// main.cpp
#include <iostream>
#include "myfunctions.h"
using namespace std;

void greet() {
    cout << "Hello from header file!" << endl;
}

int main() {
    greet();
    return 0;
}

3. Including Header Files

Use angle brackets < > for standard library headers: #include <iostream>
Use double quotes " " for custom headers: #include "myheader.h"
Header guards prevent multiple inclusion of the same header in a project.

4. Complete Example Program

              
            
C++

          Using standard and custom header files
        
// utils.h
#ifndef UTILS_H
#define UTILS_H
void printMessage();
#endif

// utils.cpp
#include <iostream>
#include "utils.h"
using namespace std;
void printMessage() { cout << "Hello from utils!" << endl; }

// main.cpp
#include <iostream>
#include "utils.h"
using namespace std;

int main() {
    printMessage();
    return 0;
}

Conclusion

C++ header files allow modular programming by separating declarations from implementation. Using standard and custom headers properly improves code organization, reusability, and readability.