code generating wreorder warning

I have the following class

#include <string>

class A {
 protected:
   std::string m1;
   int port;

 public:
   std::string m2;
   A(std::string,std::string,int);


};

A::A(std::string _m1,std::string _m2,int _port) : m1(_m1),m2(_m2),port(_port){
}

int main(int argc, char *argv[]){
  A("x","y",argc);
}

when compiled with gcc ARM 5.40 and -Wreorder it outputs

a.cpp: In constructor ‘A::A(std::__cxx11::string, std::__cxx11::string, int)’:
a.cpp:9:16: warning: ‘A::m2’ will be initialized after [-Wreorder]
    std::string m2;
                ^
a.cpp:6:8: warning:   ‘int A::port’ [-Wreorder]
    int port;
        ^

a.cpp:15:1: warning:   when initialized here [-Wreorder]
 A::A(std::string _m1,std::string _m2,int _port) : m1(_m1),m2(_m2),port(_port){
 ^

1.- Why does it generate the warning ? 2.- Will m2 and port have default value or value assigned in main ? 3.- Why it does not happen with m1 ? 4.- Is this a correct way to initialize member variables ?