C++对已经声明的变量显示未声明

Question

对于已经声明的engine显示未声明，并且竟然Engine类也显示未声明，很困惑。

Answer 1

注意delete和new的对应 这个报错我还真没看出来问题，除非把你代码贴出来调一下
我简单试了一下是没啥问题的

#include <iostream>
#include <string>
using namespace std;
#include <stdio.h>

class Engine {
private:
    string* engine;
public:
    ~Engine();
    Engine(string engine_);
    void printstr()
    {
        printf("%s \n", engine->c_str());
    };

};
Engine::~Engine()
{
    delete engine;
}

Engine::Engine(string engine_)
{
    engine = new string(engine_);
}

int main()
{
    Engine ll("123");
    ll.printstr();

    string* str;
    string str1 = "123";
    str = new string(str1);
    printf("%s \n", str->c_str());
    delete str;
    return 0;
}