结构和其他结构内部的双指针，多层混淆

Question

所以我有三个带函数的结构……

struct Song{
    std::string songTitle;
    std::string songLength;
};
Song* createSong(string title, string length);
void displaySong(Song* s);
void destroySong(Song* s);

struct CD{
    std::string cdArtist;
    std::string cdTitle;
    int cdYear;
    int cdRate;
    int cdNumSongs;
    Song** songs;
};
CD* createCD(std::string artist, std::string title, int year, int rate, int numSongs);
void displayCD(CD* c);
void destroyCD(CD* c);
void addSong(CD* cd, std::string title, std::string length);

struct CDs{
    CD** cdArray;
    int cdMaxSize=1000;
    int cdCurrentSize=0;
};
CDs* createCDs (const char* filename);
void displayCDs (CDs* c);
void destoryCDs (CDs* c);

我已经创建并测试了struct Song的函数以及struct CD的函数。然而，我在实现CDs* createCDs (const char* filename)时遇到了麻烦，它从一个文件中获取内容，并从这些CDs中创建一个动态存储的数组。

到目前为止，这是我的代码，我检查了悬空指针，当我的代码编译时，它运行得很好。就在运行的时候，它会停下来几秒钟，然后退出。从文本文件中读取数据也经过了测试，该部分可以自行工作。

到目前为止..。

CDs* createCDs(const char* filename){
    CDs* cds = new CDs;
    ifstream inFile(filename);

    CD* tempcd;
    CD** tempcdArray = new CD*[cds->cdCurrentSize];
    CD** tempcdNewArray;

    string tempArtist, tempTitle, tempSongTitle, tempSongLength;
    int tempYear, tempRate, tempNumSongs;

    while(getline(inFile, tempTitle)){ // WHEN IT GRABS NOTHING
        cds->cdMaxSize++;
        tempcdNewArray = new CD*[cds->cdMaxSize];
        for(int i=0; i<cds->cdCurrentSize; i++){
            tempcdNewArray[i] = tempcdArray[i];
            delete[] tempcdArray;
        }

        getline(inFile, tempArtist);
        inFile>>tempYear;
        inFile>>tempRate;
        inFile>>tempNumSongs;
        inFile.ignore();
        tempcd = createCD(tempArtist, tempTitle, tempYear, tempRate, tempNumSongs);
        for(int i=0; i<tempNumSongs; i++){
            getline(inFile, tempSongLength, ',');
            getline(inFile, tempSongTitle);
            addSong(tempcd, tempSongTitle, tempSongLength);
        }

        tempcdNewArray[cds->cdCurrentSize] = tempcd;
        tempcdArray = new CD*[cds->cdMaxSize];
        for(int i=0; i<cds->cdMaxSize; i++){
            tempcdArray[i] = tempcdNewArray[i];
            delete tempcdNewArray;
        }
        delete[] tempcd;
        cds->cdCurrentSize++;

    }
    for(int i=0; i<cds->cdCurrentSize; i++){
        cds->cdArray[i] = tempcdArray[i];
    }
    inFile.close();
    return cds;
}

如果您需要知道，文本文件布局中的一张cd是..

Eternal Tears of Sorrow (cd title)
Saivon Lapsi (cd artist)
2013 (cd year)
7 (cd rating)
13 (number of songs)
1:10,Saivo (length, title)
... (other songs after here)

我试着跟踪我的代码的悬空指针，我确保我‘新’的所有部分的内存我返回..等等。

Answer 1

我会尽可能长时间地远离new/delete，我还会把对你的structs进行操作的函数移到structs中，或者至少让它们成为加好友的函数。使用标准容器(如std::vector)进行存储。我用流运算符替换了用于读取和显示对象的函数，以便更容易地使用标准流进行读/写。这将以您指定的格式读取文件，然后将创建的对象以与原始文件中相同的格式流式传输到std::cout。

#include <iostream>
#include <vector>
#include <fstream>
#include <iterator>

class Song {
    std::string m_title;
    std::string m_length;
public:
    Song() : m_title(), m_length() {}
    friend std::ostream& operator<<(std::ostream&, const Song&);
    friend std::istream& operator>>(std::istream&, Song&);
};

std::ostream& operator<<(std::ostream& os, const Song& song) {
    os << song.m_length << "," << song.m_title;
    return os;
}

std::istream& operator>>(std::istream& is, Song& song) {
    std::string tmp;
    std::getline(is, tmp);
    std::string::size_type comma = tmp.find(",");
    if(comma != std::string::npos) {
        std::copy(tmp.cbegin(), tmp.cbegin()+comma, std::inserter(song.m_length, song.m_length.end()));
        std::copy(tmp.cbegin()+comma+1, tmp.cend(), std::inserter(song.m_title, song.m_title.end()));
    }
    return is;
}

class CD {
    std::string m_artist;
    std::string m_title;
    int m_year;
    int m_rate;
    std::vector<Song> m_songs;
public:
    CD() :
        m_artist(),
        m_title(),
        m_year(),
        m_rate(),
        m_songs()
    {}
    size_t size() { return m_songs.size(); }
    friend std::ostream& operator<<(std::ostream&, const CD&);
    friend std::istream& operator>>(std::istream&, CD&);    
};

std::ostream& operator<<(std::ostream& os, const CD& cd) {
    os << cd.m_title << "\n" << cd.m_artist << "\n" << cd.m_year << "\n"
       << cd.m_rate << "\n" << cd.m_songs.size() << "\n";
    for(const Song& song : cd.m_songs) {
        os << song << "\n";
    }
    return os;
}

std::istream& operator>>(std::istream& is, CD& cd) {
    int no_songs;
    std::getline(is, cd.m_title);
    std::getline(is, cd.m_artist);
    is >> cd.m_year;
    is >> cd.m_rate;
    is >> no_songs;
    is.ignore(); // discard rest of line
    cd.m_songs.reserve(no_songs);
    while(no_songs--) {
        Song a_song;
        is >> a_song;
        cd.m_songs.emplace_back(std::move(a_song));
    }
    return is;
}

class CDs {
    std::vector<CD> m_cds;
public:
    CDs() : m_cds() {}
    CDs(const std::string& Filename) :
        m_cds()
    {
        std::fstream cdfile(Filename);
        cdfile >> *this;
    }
    size_t size() { return m_cds.size(); }
    friend std::ostream& operator<<(std::ostream&, const CDs&);
    friend std::istream& operator>>(std::istream&, CDs&);
};

std::ostream& operator<<(std::ostream& os, const CDs& cds) {
    for(const CD& cd : cds.m_cds) os << cd;
    return os;
}

std::istream& operator>>(std::istream& is, CDs& cds) {
    while( !is.eof() ) {
        CD a_cd;
        is >> a_cd;
        if( !is.eof() ) cds.m_cds.emplace_back(a_cd);
    }
    return is;
}

int main(int argc, char* argv[]) {
    std::vector<std::string> args(argv+1, argv+argc);

    CDs cds;
    for(const std::string& file : args) {
        std::fstream fs(file);
        fs >> cds;
    }
    std::cerr << "Number of CDs: " << cds.size() << "\n";
    std::cout << cds;
    return 0;
}