返回值后刪除指針

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);
}

我認為我有內存泄漏，如何在返回指針后刪除指針？ 我如何使用析構函數釋放內存，但遇到運行時錯誤bad：alloc

Answer 1

像@BalogPal所說的那樣，最簡單的解決方法是停止像Java那樣對待C ++。 沒有理由從任何這些函數中返回指針。 嘗試這樣的事情：

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);
}

我將參數保留為指針的唯一原因是TiXmlElement的FirstChildElement()和NextSiblingElement()函數返回的結果。 通常，我會改為TiXmlElement &element引用（ TiXmlElement &element ），這更加安全，因為您不能傳遞NULL 。

如果出於性能原因確實需要避免復制，並且編譯器不夠智能，無法自動執行該操作，則可以使用智能指針 ，這些指針已被引用計數，因此您不必擔心delete它們。

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.

Answer 2

通常，您不會“返回”指針。 您可以將指針作為參數傳遞給函數，並在函數中為其分配一個值。 由於指針是內存位置，因此函數返回時，此值將保留在指針中。 將指針用於所需的對象之后，即可進行任何內存管理。