未定义对 C++ 中 Class 结构向量的 static 向量的引用 [暂停]

Question

I want to declare a static vector of structures inside a Class and then use it inside the class functions. But it keeps giving me errors:

undefined reference

First, I tried a simple code without using a structure. The following code runs without any errors:

#include <iostream>
#include <vector>
using namespace std;

class CACHE
{
    public:
        static vector<int> gtt;

        CACHE(int index, int value){
            gtt[index]=value;
        }

        void show_gtt(){
            for(int i=0; i<4; i++){
                cout<<gtt[i]<<'\n';
            }
            cout<<'\n';
        }
};

//Initializing 4 values
vector<int> CACHE::gtt = vector<int>(4);

int main(){

    CACHE L1(1, 78);
    L1.show_gtt();
    CACHE L2(2, 55);
    L2.show_gtt();

    return 0;
}

I know that I can have maximum 4 objects hence the use of '4' in functions and initialization. The output is as follows:

0
78
0
0

0
78
55
0

Now, I try the same concept but with the use of Structure as follows:

#include <iostream>
#include <vector>
using namespace std;

struct gtt_struct
{
    static int  x;
    static int  y;
};

class CACHE
{
    public:
        static vector<gtt_struct> gtt;

        CACHE(int index, int value_1, int value_2){
            gtt[index].x=value_1;
            gtt[index].x=value_2;
        }

        void show_gtt(){
            for(int i=0; i<4; i++){
                cout<<"["<<gtt[i].x<<", "<<gtt[i].y<<"]\n";
            }
            cout<<'\n';
        }
};

//Initializing 4 values
vector<gtt_struct> CACHE::gtt = vector<gtt_struct>(4);

int main(){

    CACHE L1(1, 78, 33);
    L1.show_gtt();
    CACHE L2(2, 55, 49);
    L2.show_gtt();

    return 0;
}

The above code gives me the following compilation error:

/tmp/ccijWpnu.o: In function `CACHE::CACHE(int, int, int)':
test_1.cpp:(.text._ZN5CACHEC2Eiii[_ZN5CACHEC5Eiii]+0x2e): undefined reference to `gtt_struct::x'
test_1.cpp:(.text._ZN5CACHEC2Eiii[_ZN5CACHEC5Eiii]+0x4b): undefined reference to `gtt_struct::x'
/tmp/ccijWpnu.o: In function `CACHE::show_gtt()':
test_1.cpp:(.text._ZN5CACHE8show_gttEv[_ZN5CACHE8show_gttEv]+0x4a): undefined reference to `gtt_struct::x'
test_1.cpp:(.text._ZN5CACHE8show_gttEv[_ZN5CACHE8show_gttEv]+0x80): undefined reference to `gtt_struct::y'
collect2: error: ld returned 1 exit status

I think I have followed the initialization guidelines as mentioned in other posts. But it seems that the structure syntax is causing the issue. Is the syntax gtt[index].x incorrect? Or is it some other C++ conceptual problem?

Answer 1

you defined x and y static. So use them like: gtt[index]::x, ::y