LNK2005，链接时提示构造函数和析构函数重复定义，新手求教

#ifndef Str_my_H
#define Str_my_H
#define Maxsize 20

class Str_my{
    private:
        char *data;
    public:
        Str_my();
        Str_my(char a[],int n);
        ~Str_my();
        int StrLen();
        char * StrCat();
        int StrCmp();
};

#endif

#include<iostream>
#include<stdlib.h>
#include"Str_my.h"
using namespace std;

Str_my::Str_my(){
    data=(char * )malloc(sizeof(char)*Maxsize);
}

Str_my::Str_my(char a[],int n){
    data=(char * )malloc(sizeof(char)*Maxsize);
    for(int i=0;i<n;i++){
        *(data+i)=a[i];
    }
    *(data+n)='\0';
}

Str_my::~Str_my(){
    if(data!=NULL) free(data);
}

#include<iostream>
#include<stdlib.h>
#include"Str_my.h"
#include"Str_my.cpp"
using namespace std;

int main(){
    Str_my S1;
    char a[4]={'C','J','L','!'};
    Str_my S2(a,4);
    return 0;
}

Deleting intermediate files and output files for project '字符串的实现 - Win32 Debug'.
--------------------Configuration: 字符串的实现 - Win32 Debug--------------------
Compiling...
Str_my.cpp
Str_my_main.cpp
Linking...
Str_my_main.obj : error LNK2005: "public: __thiscall Str_my::Str_my(void)" (??0Str_my@@QAE@XZ) already defined in Str_my.obj
Str_my_main.obj : error LNK2005: "public: __thiscall Str_my::Str_my(char * const,int)" (??0Str_my@@QAE@QADH@Z) already defined in Str_my.obj
Str_my_main.obj : error LNK2005: "public: __thiscall Str_my::~Str_my(void)" (??1Str_my@@QAE@XZ) already defined in Str_my.obj
Debug/字符串的实现.exe : fatal error LNK1169: one or more multiply defined symbols found
执行 link.exe 时出错.

字符串的实现.exe - 1 error(s), 0 warning(s)