c++ - 返回值后删除指针

Question

你好我有以下功能:

Block* Keywords::parseBlock(TiXmlElement* element)
{
    double x1 = atoi(element->Attribute("left"));
    double y1 = atoi(element->Attribute("top"));
    double x2 = atoi(element->Attribute("right"));
    double y2 = atoi(element->Attribute("bottom"));
    double width  = abs(x2 - x1);
    int bid = atoi(element->Attribute("id"));

    vector<LineElement*> lines;
    for (TiXmlElement* sub = element->FirstChildElement("line"); sub; sub = sub->NextSiblingElement("line"))
        lines.push_back(parseLine(sub));

    return new Block(y2,x2,y1,x1,bid,width, lines);
}///End function parse Block

LineElement* Keywords::parseLine(TiXmlElement* element)
{
    double x1 = atoi(element->Attribute("left"));
    double y1 = atof(element->Attribute("top"));
    double x2 = atoi(element->Attribute("right"));
    double y2 =  atoi(element->Attribute("bottom"));
    int bid = atoi(element->Attribute("id"));

    vector<Element*> words;
    for (TiXmlElement* sub = element->FirstChildElement("word"); sub; sub = sub->NextSiblingElement("word"))
        words.push_back(parseWord(sub));

    return new LineElement(y2,x2,y1,x1,bid,words);
}///End function parse Line

Element * Keywords::parseWord(TiXmlElement* element)
{
    string w =element->Attribute("value");
    double x1 = atoi(element->Attribute("left"));
    double y1 = atoi(element->Attribute("top"));
    double x2 = atoi(element->Attribute("right"));
    double y2 = atoi(element->Attribute("bottom"));
    int bid = atoi(element->Attribute("id"));

    vector<Letter*> chars;

    for (TiXmlElement* sub = element->FirstChildElement("char"); sub; sub = sub->NextSiblingElement("char"))
        chars.push_back(parseChar(sub));

    return new  Element(w,y1, x1, y2,x2,-1,bid,chars);
}///End function parse word

Letter * Keywords::parseChar(TiXmlElement* element)
{
    string w = element->Attribute("value");
    double x1 = atoi(element->Attribute("left"));
    double y1 = atoi(element->Attribute("top"));
    double x2 = atoi(element->Attribute("right"));
    double y2 =  atoi(element->Attribute("bottom"));
    int bid = atoi(element->Attribute("id"));
    return new Letter(w,y1,x1,y2,x2,bid);
}

我认为我有内存泄漏，如何在返回后删除指针？ 我如何使用析构函数释放内存我收到运行时错误 bad:alloc

Answer 1

如@BalogPal 所说，解决此问题的最简单方法是停止像对待 Java 一样对待 C++。没有理由从任何这些函数返回指针。尝试这样的事情:

Block Keywords::parseBlock(TiXmlElement* element)
{
    double x1 = atoi(element->Attribute("left"));
    double y1 = atoi(element->Attribute("top"));
    double x2 = atoi(element->Attribute("right"));
    double y2 = atoi(element->Attribute("bottom"));
    double width = abs(x2 - x1);
    int bid = atoi(element->Attribute("id"));

    vector<LineElement> lines;
    for (TiXmlElement* sub = element->FirstChildElement("line"); sub; sub = sub->NextSiblingElement("line"))
        lines.push_back(parseLine(sub));

    return Block(y2, x2, y1, x1, bid, width, lines);
}

LineElement Keywords::parseLine(TiXmlElement* element)
{
    double x1 = atoi(element->Attribute("left"));
    double y1 = atof(element->Attribute("top"));
    double x2 = atoi(element->Attribute("right"));
    double y2 = atoi(element->Attribute("bottom"));
    int bid = atoi(element->Attribute("id"));

    vector<Element> words;
    for (TiXmlElement* sub = element->FirstChildElement("word"); sub; sub = sub->NextSiblingElement("word"))
        words.push_back(parseWord(sub));

    return LineElement(y2, x2, y1, x1, bid, words);
}

Element Keywords::parseWord(TiXmlElement* element)
{
    string w = element->Attribute("value");
    double x1 = atoi(element->Attribute("left"));
    double y1 = atoi(element->Attribute("top"));
    double x2 = atoi(element->Attribute("right"));
    double y2 = atoi(element->Attribute("bottom"));
    int bid = atoi(element->Attribute("id"));

    vector<Letter> chars;

    for (TiXmlElement* sub = element->FirstChildElement("char"); sub; sub = sub->NextSiblingElement("char"))
        chars.push_back(parseChar(sub));

    return Element(w, y1, x1, y2, x2, -1, bid, chars);
}

Letter Keywords::parseChar(TiXmlElement* element)
{
    string w = element->Attribute("value");
    double x1 = atoi(element->Attribute("left"));
    double y1 = atoi(element->Attribute("top"));
    double x2 = atoi(element->Attribute("right"));
    double y2 = atoi(element->Attribute("bottom"));
    int bid = atoi(element->Attribute("id"));
    return Letter(w, y1, x1, y2, x2, bid);
}

我将参数保留为指针的唯一原因是这就是您的 TiXmlElement 的 FirstChildElement() 和 NextSiblingElement() 函数返回的内容。通常，我会让它们成为引用 (TiXmlElement &element)，这样更安全，因为您不能传递 NULL。

如果您出于性能原因确实需要避免复制，并且您的编译器不够智能，无法自动执行此操作，您可以使用 smart pointers ，它们是引用计数的，因此您无需担心删除它们。

std::shared_pointer<Block> Keywords::parseBlock(TiXmlElement* element)
{
    double x1 = atoi(element->Attribute("left"));
    double y1 = atoi(element->Attribute("top"));
    double x2 = atoi(element->Attribute("right"));
    double y2 = atoi(element->Attribute("bottom"));
    double width = abs(x2 - x1);
    int bid = atoi(element->Attribute("id"));

    vector<std::shared_pointer<LineElement> > lines;
    for (TiXmlElement* sub = element->FirstChildElement("line"); sub; sub = sub->NextSiblingElement("line"))
        lines.push_back(parseLine(sub));

    return std::shared_pointer<Block>(new Block(y2, x2, y1, x1, bid, width, lines));
}

// etc.