STATUS_ACCESS_VIOLATION读取文件int struct [英] STATUS_ACCESS_VIOLATION when reading file int struct

问题描述

我正在阅读3个东西到一个结构歌曲：songtitle，艺术家，文件大小。我运行程序时遇到错误，它看起来是正确的。

I am reading 3 things into a struct Songs: songtitle, artist, size of file. I am getting a error when i run the program, tho it looks correct.

#include <iostream>
#include <string>
#include <sstream>
#include <fstream>
using namespace std;

struct Songs
{
    string title;
    string artist;
    int size;
};

int main ()
{
    int num_songs;

    Songs song[num_songs];

    ifstream fin;
    fin.open("songlist.txt")

    while (fin.good()) {
        fin >> song[num_songs].title;
        fin >> song[num_songs].artist;
        fin >> song[num_songs].size;
        num_songs++;
    }
    fin.close();

    cout << "welcome to the show" << endl;
    return 0;
}

为什么程序产生 STATUS_ACCESS_VIOLATION 将文件读入 struct ？

Why does the program produce STATUS_ACCESS_VIOLATION when reading the file into a struct?

推荐答案

程序没有看起来正确，它有一些错误，详细在其他答案。

You program doesn't "look correct", it has a number of errors, detailed in other answers.

这是一个正确读取歌曲列表的程序。请注意，这是用于读取文件的四种替代方法。选择最有意义的一个，并删除其他三个。

Here is a program that correctly reads in the song list. Note that these are four alternative methods for reading the file. Choose the one that makes the most sense to you and delete the other three.

#include <iostream>
#include <string>
#include <sstream>
#include <fstream>
#include <vector>
#include <iterator>
#include <algorithm>

struct Song
{
    std::string title;
    std::string artist;
    int size;
    Song() : size() { }
    Song(const Song& song) :
      title(song.title), artist(song.artist), size(song.size) { }
    Song(std::string title, std::string artist, int size) :
      title(title), artist(artist), size(size) { }
};

std::istream&
operator>>(std::istream& is, Song& song) {
    return is >> song.title >> song.artist >> song.size;
}

int main ()
{    
   std::vector< Song > songs;

   std::ifstream fin;
   fin.open("songlist.txt");

   // You could read the songs this way:
   std::copy(std::istream_iterator<Song>(fin),
       std::istream_iterator<Song>(),
       std::back_inserter(songs));

   // Or, if you don't like std::copy, you can do this:
   Song song;
   while(fin >> song)
       songs.push_back(song);

   // Or, if you don't like operator>>(istream, Song), you can do this:
   std::string artist;
   std::string title;
   int size;
   while(fin >> artist >> title >> size)
       songs.push_back(Song(artist, title, size));

   // Or, if you don't like using the constructor:
   while(fin >> artist >> title >> size) {
       Song song;
       song.artist = artist;
       song.title = title;
       song.size = size;
       songs.push_back(song);
    }


    int num_songs = songs.size();
    std::cout << "welcome to the show: " << num_songs << "\n";
    return 0;
}

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