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demo1只有类的情况下调用

下面写一个util.h 文件里面

// 定义宏防止编译器重复编译
#ifndef TEST_H
#define TEST_H
class Test{
public:void sum(int a, int b);int num(int a, int b);bool number();};
#endif // TEST_H

调用的时候首先要引入这个头文件 #include "util.h"

cpp 里面实现

#include <iostream>
#include <string>
#include "util.h"
using namespace std;// 实现Test类的sum成员函数
void Test::sum(int a,int b){cout << "The sum of " << a << " and " << b << " is: " << a + b << std::endl;
}
// 实现Test类的num成员函数
int Test::num(int a, int b) {return a * b;
}
// 实现Test类的number成员函数
bool Test::number() {return true;
}int main() {int a =3;int b =6;Test test;test.sum(a,b);int result = test.num(a,b);cout<< "num result" << result <<endl;bool isNumber = test.number();cout<< "number result" << isNumber <<endl;return 0;
}

demo2 有namespace的情况下调用

util.h 文件

// 定义宏防止编译器重复编译
#ifndef TEST_H
#define TEST_H
namespace common::comm::com {
class Test{
public:void sum(int a, int b);int num(int a, int b);bool number();};
}
#endif  

cpp 里面实现，这里不使用using namespace

#include <iostream>
#include <string>
#include "util.h"
using namespace std;// 实现Test类的sum成员函数
void common::comm::com::Test::sum(int a,int b){cout << "The sum of " << a << " and " << b << " is: " << a + b << std::endl;
}
// 实现Test类的num成员函数
int common::comm::com::Test::num(int a, int b) {return a * b;
}
// 实现Test类的number成员函数
bool common::comm::com::Test::number() {return true;
}int main() {int a =3;int b =6;common::comm::com::Test test;test.sum(a,b);int result = test.num(a,b);cout<< "num result" << result <<endl;bool isNumber = test.number();cout<< "number result" << isNumber <<endl;return 0;
}

使用using namespace

namespace common::comm::com {
// 实现Test类的sum成员函数
void Test::sum(int a,int b){cout << "The sum of " << a << " and " << b << " is: " << a + b << std::endl;
}
// 实现Test类的num成员函数
int Test::num(int a, int b) {return a * b;
}
// 实现Test类的number成员函数
bool Test::number() {return true;
}
}
int main() {int a =3;int b =6;using namespace common::comm::com;Test test;test.sum(a,b);int result = test.num(a,b);cout<< "num result" << result <<endl;bool isNumber = test.number();cout<< "number result" << isNumber <<endl;return 0;
}

实际用不用，根据个人习惯即可，不使用using namespace在每次调用时都写出完整的命名空间路径

把util.h 文件修改一层一层的

// 定义宏防止编译器重复编译
#ifndef TEST_H
#define TEST_H
namespace common{namespace comm{namespace com{class Test{public:void sum(int a, int b);int num(int a, int b);bool number();};}}
}
#endif  

实现里面的方法效果也是一样的

#include <iostream>
#include <string>
#include "util.h"
using namespace std;namespace common::comm::com {
// 实现Test类的sum成员函数
void Test::sum(int a,int b){cout << "The sum of " << a << " and " << b << " is: " << a + b << std::endl;
}
// 实现Test类的num成员函数
int Test::num(int a, int b) {return a * b;
}
// 实现Test类的number成员函数
bool Test::number() {return true;
}
}
int main() {int a =3;int b =6;using namespace common::comm::com;Test test;test.sum(a,b);int result = test.num(a,b);cout<< "num result" << result <<endl;bool isNumber = test.number();cout<< "number result" << isNumber <<endl;return 0;
}

或者

#include <iostream>
#include <string>
#include "util.h"
using namespace std;namespace common {namespace comm {namespace com {// 实现Test类的sum成员函数void Test::sum(int a, int b) {std::cout << "The sum of " << a << " and " << b << " is: " << a + b << std::endl;}int Test::num(int a, int b) {return a * b;}bool Test::number() {return true; // 示例返回true}} // 结束命名空间 com} // 结束命名空间 comm
} // 结束命名空间 common
int main() {int a =3;int b =6;using namespace common::comm::com;Test test;test.sum(a,b);int result = test.num(a,b);cout<< "num result" << result <<endl;bool isNumber = test.number();cout<< "number result" << isNumber <<endl;return 0;
}