命名空间和模块化编程,头文件

#include <iostream>
#include <string>
#include "dynamic_memory.h"

Company::Company(std::string theName)
{
    name = theName;
};

void Company::printInfo()
{
    std::cout << "this company's name is " << name << std::endl;
};

TechCompany::TechCompany(std::string theName, std::string theproduct) : Company(theName)
{
    product = theproduct;
};

void TechCompany::printInfo()
{
    std::cout << "this company's name is " << name << " his product is " << product << std::endl;
}

int main()
{
    Company *company = new Company("Apple");
    company->printInfo();

    delete company;
    company = NULL;

    company = new TechCompany("Apple", "Iphone");
    company->printInfo();

    delete company;
    company = NULL;

}
/* vim: set ts=4 sw=4 sts=4 tw=100 */

预处理命令，避免重复编译
#ifndef DYNAMIC_MEMORY_H_INCLUDED 名字要保持一致，为了方便团队编程
#define DYNAMIC_MEMORY_H_INCLUDED

class Company
{
public:
    Company(std::string theName);
    virtual void printInfo();

protected:
    std::string name;
};

class TechCompany : public Company
{
public:
    TechCompany(std::string theName, std::string product);
    virtual void printInfo();
private:
    std::string product;
};

#endif // DYNAMIC_MEMORY_H_INCLUDED

命名空间
#include <iostream>
using namespace std;
namespace a
{
void print();

void print(){
   cout << "hello world from namespace a" << endl;
}
}

namespace b{
void print();
void print(){
    cout << "hello world from namespace b" << endl; 
}
}

int main()
{
    a::print();
    b::print();
　　 std:cout << "hello" << std:endl;  提倡
     using namespace std; 整个命名空间全局化违背了命名空间的设计意图。不提倡
     using std::cout    只给cout全局性， OK
     只放在某个函数里，那么它只能在这一个函数里使用。

}