如何搜索对象指针列表？C++

Question

首先，这是一项人为限制的分配。作业要求我使用 STL、继承和多态性。我还必须使用迭代器根据对象 ID 从列表中查找、打印和删除项目。

我正在使用指向对象的指针列表。这些对象派生自抽象基类 Sequence，并且动态分配并存储在列表中。

我的抽象基类

class Sequence{
public:
    virtual void print() = 0;
    virtual int getId() = 0;


protected:
    std::string m_label;
    int m_id;
    std::string m_sequence;
    int m_length;

};

和函数在派生类中被重写print()。getId()数据从文件中读入，并通过每行命令进行解析。

SequenceDatabase::SequenceDatabase(){

    std::list<Sequence*> myList;
}

// function reads in the filename creates a data stream and performs the requested actions
void SequenceDatabase::importEntries(std::string inputFile){
    std::ifstream dnaFile(inputFile);
    char command;
    std::string label, sequence, type;
    int id, length, index, orf; 
    while(dnaFile >> command){
        Sequence* s;
        // if the command = D this allocates memory for a dna object and pushes the object onto the list
        if(command == 'D'){
            dnaFile >> label >> id >> sequence >> length >> index;
            std::cout << "Adding " << id << " ...\n\n";
            s = new DNA(label, id, sequence, length, index);
            myList.push_back(s);
        }
        // if the command = R this allocates memory for a RNA object and pushes the object onto the list
        if(command == 'R'){
            dnaFile >> label >> id >> sequence >> length >> type;
            std::cout << "Adding " << id << " ...\n\n";
            s = new RNA(label, id, sequence, length, type);
            myList.push_back(s);
        }
        // if the command = A this allocates memory for an AA object and pushes the object onto the list
        if(command == 'A'){
            dnaFile >> label >> id >> sequence >> length >> orf;
            std::cout << "Adding " << id << " ...\n\n";
            s = new AA(label, id, sequence, length, orf);
            myList.push_back(s);
        }
        // if the command = O this searches the list for the id and either outputs that the object doesn't exist or it deletes it
        if(command == 'O'){
            dnaFile >> id;
            std::cout << "Obliterating " << id << " ...\n\n";
            // problem
        }
        // if the command = P this searches the lists for the id and either outputs that the object doesn't exist or it prints out the info of the object 
        if(command == 'P'){
            dnaFile >> id;
            std::cout << "Printing " << id << " ...\n";
            // problem  
        }
        // if the command = S this outputs the number of entries in the list
        if(command == 'S')
            std::cout << "Entries: " << myList.size() << " total\n";
    }
    dnaFile.close();
}

该列表正在正确构建。当尝试在列表中搜索具有特定 id 的对象时，出现了我的问题。我创建了这个findId()函数，因为我知道我必须将其与读入的 id 进行比较。

我不确定在处理对象指针时如何使用std::find或函数。std::find_if我已经尝试了几个小时，但我尝试的每件事都无法编译。

任何帮助表示赞赏。谢谢你！

Answer 1

如果您有权使用 C++11 编译器，则可以使用：

auto iter = std::find_if(myList.begin(),
                         myList.end(),
                         [](Sequence* s) -> bool { return (s->getId() == id); });
if ( iter != myList.end() )
{
   return *iter;
}
else
{
   return nullptr;
}

std::find_if搜索谓词返回 的元素true。其他信息可以在http://en.cppreference.com/w/cpp/algorithm/find找到。

在本例中，谓词是一个 lambda 函数，true如果给定 ID 与其中一个Sequence*对象的 ID 匹配，则该函数返回。

如果列表不包含匹配的Sequence*，find_if则返回myList.end()。