header files for c++ code example

Example 1: what is a header in c++

// my_class.h
#ifndef MY_CLASS_H // include guard
#define MY_CLASS_H

namespace N
{
    class my_class
    {
    public:
        void do_something();
    };
}

#endif /* MY_CLASS_H */

Example 2: c++ header files

// You should use header files when you wan't to split your
// program across multiple files. Use it like this:

// vec2.hpp
class vec2 {
	public:
  		void printVec(); // Decleration
  		float x, y;
}
// vec2.cpp
#include "vec2.hpp"
void vec2::printVec() { // Implementation
	std::cout << x << y << std::endl;
}

Example 3: what is a header in c++

// sample.h
#pragma once
#include <vector> // #include directive
#include <string>

namespace N  // namespace declaration
{
    inline namespace P
    {
        //...
    }

    enum class colors : short { red, blue, purple, azure };

    const double PI = 3.14;  // const and constexpr definitions
    constexpr int MeaningOfLife{ 42 };
    constexpr int get_meaning()
    {
        static_assert(MeaningOfLife == 42, "unexpected!"); // static_assert
        return MeaningOfLife;
    }
    using vstr = std::vector<int>;  // type alias
    extern double d; // extern variable

#define LOG   // macro definition

#ifdef LOG   // conditional compilation directive
    void print_to_log();
#endif

    class my_class   // regular class definition,
    {                // but no non-inline function definitions

        friend class other_class;
    public:
        void do_something();   // definition in my_class.cpp
        inline void put_value(int i) { vals.push_back(i); } // inline OK

    private:
        vstr vals;
        int i;
    };

    struct RGB
    {
        short r{ 0 };  // member initialization
        short g{ 0 };
        short b{ 0 };
    };

    template <typename T>  // template definition
    class value_store
    {
    public:
        value_store<T>() = default;
        void write_value(T val)
        {
            //... function definition OK in template
        }
    private:
        std::vector<T> vals;
    };

    template <typename T>  // template declaration
    class value_widget;
}

Example 4: c++ header files example

//headers 
#ifndef TOOLS_hpp 
#define TOOLS_hpp
#include<vector> 
#include<iostream>
#include<fstream>
#include<string>
using std::ifstream;
using std::cout; 
using std::cin;
using std::endl;
using std::cerr;
using std::vector;
using std::string;
// functions prototypes 
inline vector<int> merge(const vector<int>&a,const vector<int>& b);//merge function prototype with Formal Parameters 
std::vector<int> sort(size_t start, size_t length, const std::vector<int>& vec);//sort function prototype with formal parameters 
#endif