C++ string assignment error. How to assign values to a string member of a struct pointer?

Why the output of codes below is an invalid string? If lines #1 to #3 cannot be changed, how can I assign the value of config.strConfig to data2->str?

// classA.h
#pragma once
#include <string>

class Config {
public:
    int a;
    std::string strConfig;
};

// structA.h
#pragma once

#include <string>

struct Data {
    char test[2];
    std::string str;
};

// main.cpp
#include "classA.h"
#include "structA.h"
#include <iostream>

int main() {
    Data data;  // #1
    memset(&data, 0, sizeof(data));  // #2
    Data* data2 = &data;   // #3
    Config config;         
    config.strConfig = "aaaa";
    data2->str = config.strConfig;
    std::cout << (data2->str) << std::endl;
}