Question

似乎对Feed向量的迭代不会调用绘图函数。我在里面添加了一些断点，但没有一个断点被触发。

数据是我程序其他部分提供的字符串向量，它可以正常工作（输出文件很好）。

std::vector<std::unique_ptr<NewsRenderer>> feed;

std::unique_ptr<NewsRenderer> ptr=std::make_unique<NewsRenderer>(NewsRenderer(sf::Vector2i(300, 100), "test-title", "test-url"));
feed.push_back(std::move(ptr));

myfile.close();

while (window.isOpen())
{
    window.clear(sf::Color::White);
    for (int i = 0; i < feed.size(); i++)
    {
        feed[i]->draw(0, 100 * i);
    }

    window.display();
}

有NewsRenderer.h

#include "News.h"

#include <iostream>
class NewsRenderer
{
public:
    NewsRenderer(std::string title, std::string url, std::string decription="");
    void draw(int x, int y);
    ~NewsRenderer();
private:
    News* newsData;
};

和NewsRenderer.cpp

NewsRenderer::NewsRenderer(std::string title, std::string url, std::string decription)
{
    newsData = new News{ title, url, decription };
}

void NewsRenderer::draw(int x, int y)
{
    draw(title, x, y); //magic, but I didn't want to use any libraries in this example
}

NewsRenderer::~NewsRenderer()
{
}

所以我的问题是：发生了什么？我该如何解决？

PS。我试着保持简单，所以如果我跳过任何重要的细节让我知道，我会交付。

Answer 1

#include <vector>
#include <string>
#include <memory>
#include <iostream>

struct News {
    const std::string title;
    const std::string url;
    const std::string description;
};

struct NewsRenderer {
    NewsRenderer(std::string title, std::string url, std::string description="")
    : data(new News{title, url, description})
    { }

    ~NewsRenderer()
    { delete data; }

    void draw() const
    { std::cout << data->title << " - " << data->url << " - " << data->description << '\n'; }

    const News* data;
};

void foo() {
    std::cout << "foo()\n";
    std::vector<std::unique_ptr<NewsRenderer>> feed{};

    auto p = std::make_unique<NewsRenderer>("title", "url", "description");
    //                                      ^^^^^^^^^^^^ <= forwards arguments to NewsRenderers constructor
    feed.push_back( std::move(p) );
    for(auto& nr : feed) nr->draw();
}

void bar() {
    std::cout << "bar()\n";
    std::vector<std::unique_ptr<NewsRenderer>> feed{};

    auto p = std::make_unique<NewsRenderer>(NewsRenderer{"title", "url", "description"});
    //                                      ^^^^^^^^^^^^ <= tries to invoke copy constructor, not safe
    feed.push_back( std::move(p) );
    for(auto& nr : feed) nr->draw();
}

int main() {
    foo();
    bar();
    return 0;
}

对向量的迭代不会调用函数

1 个答案: