無法通過函數在向量中傳遞 ifstream 指針

Question

我正在嘗試制作一個可以生成二維城市的程序。 我正在從一個文件中獲取一個具有建築物（預定義）寬度和長度的文件，並將其傳遞給一個函數 (place_object)，該函數會將它放在文本文件中的位置。

這一切都很好，至少當我通過函數傳遞一個單一的ifstream對象時是這樣。 現在我有一個指向ifstream對象的指針向量，理論上指向我擁有的每個房子對象，因為你不能簡單地將ifstream對象傳遞給一個向量。

我在嘗試通過函數傳遞這些指針時不斷出錯。

我很難理解指針，盡管我完全理解通過引用傳遞。

#include <iostream>
#include <fstream>
#include <vector>
#include <conio2.h>
#include <constream>

using namespace std;

//...Structures...
struct Data
{
    int width;
    int height;
};

//...Global Variables...

//...Function Prototypes...
void set_data(Data&);
void init_map(vector< vector<char> >&, Data&);
void transfer_to_file(vector< vector<char> >&, ofstream&, Data&);
void place_object(int,int,ifstream*&,vector< vector<char> >&);

int main()
{
    //...Path Address Files...
    ofstream m("What_You_Need/map.txt");
    ifstream house_files("Data/File_Paths/houses.dat");
    //...Regular Variables...
    Data d;
    vector< vector<char> > map;

    //...Structures...
    vector<ifstream*> houses;


    //...Load Vectors...
    string path;
    house_files >> path;
    while(!house_files.eof())
    {
        ifstream ifstr(path.c_str());
        houses.push_back(&ifstr);
        house_files >> path;
    }

    //...Get Size...
    do
    {
        cout << "What's the map size? (HxW): ";
        cin >> d.width;
        cin.ignore(10,'x');
        cin >> d.height;
        if(cin.fail())
        {
            cin.clear();
            cin.ignore();
        }       
    }
    while((d.width < 300 || d.height < 300) || cin.fail());

    init_map(map,d);

    //...TEST CODE HERE...
    //...Structure Files...
    getch();
    place_object(3,3,houses[0],map);
    transfer_to_file(map,m,d);

    //...File Close...
    house_files.close();
    m.close();

    //...Misc...
    return 0;
}

//...Funtions...
void set_data(Data &d)
{

}

void init_map(vector< vector<char> > &map, Data &d)
{
    for (int i = 0 ; i < d.height ; i++)
    {
        vector<char> row; // Create an empty row
        for (int j = 0 ; j < d.width ; j++)
        {
            row.push_back('.'); // Add an element (column) to the row
        }
        map.push_back(row); // Add the row to the main vector
    }
}

void transfer_to_file(vector< vector<char> > &map, ofstream &o, Data &d)
{
    for(int i = 0 ; i < d.height ; i++)
    {
        for(int j = 0 ; j < d.width ; j++)
            o << map[i][j];
        o << "\n";
    }
}

void place_object(int x, int y, ifstream *&is, vector< vector<char> > &map)
{
    int width;
    int height;
    is >> width >> height;
    is.ignore(100,'\n');

    for(int i = 0 ; i < height ; i++)
    {
        string s;
        getline(is,s);
        for(int j = 0 ; j < width ; j++)
        {
            map[i+y-1][j+x-1] = s[j];
        }
        cout << endl;
    }
}

錯誤：（使用使用“new”運算符的新代碼）：

C:\Users\r_bur_000\Documents\#PROGRAMS\Map_Generator\main.cpp   In function 'void place_object(int, int, std::ifstream*&, std::vector<std::vector<char> >&)':
111 8   C:\Users\r_bur_000\Documents\#PROGRAMS\Map_Generator\main.cpp   [Error] invalid operands of types 'std::ifstream* {aka std::basic_ifstream<char>*}' and 'int' to binary 'operator>>'
112 5   C:\Users\r_bur_000\Documents\#PROGRAMS\Map_Generator\main.cpp   [Error] request for member 'ignore' in 'is', which is of pointer type 'std::ifstream* {aka std::basic_ifstream<char>*}' (maybe you meant to use '->' ?)
117 15  C:\Users\r_bur_000\Documents\#PROGRAMS\Map_Generator\main.cpp   [Error] no matching function for call to 'getline(std::ifstream*&, std::string&)'
117 15  C:\Users\r_bur_000\Documents\#PROGRAMS\Map_Generator\main.cpp   [Note] candidates are:
53  0   c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\string In file included from c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\string
40      c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\bits\locale_classes.h                   from c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\bits\locale_classes.h
41      c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\bits\ios_base.h                     from c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\bits\ios_base.h
42      c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\ios                     from c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\ios
38      c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\ostream                     from c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\ostream
39      c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\iostream                    from c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\iostream
1       C:\Users\r_bur_000\Documents\#PROGRAMS\Map_Generator\main.cpp                    from main.cpp
1068    5   c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\bits\basic_string.tcc  [Note] template<class _CharT, class _Traits, class _Alloc> std::basic_istream<_CharT, _Traits>& std::getline(std::basic_istream<_CharT, _Traits>&, std::basic_string<_CharT, _Traits, _Alloc>&, _CharT)
1068    5   c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\bits\basic_string.tcc  [Note] template argument deduction/substitution failed:
117 15  C:\Users\r_bur_000\Documents\#PROGRAMS\Map_Generator\main.cpp   [Note] mismatched types 'std::basic_istream<_CharT, _Traits>' and 'std::ifstream* {aka std::basic_ifstream<char>*}'
52  0   c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\string In file included from c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\string
40      c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\bits\locale_classes.h                   from c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\bits\locale_classes.h
41      c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\bits\ios_base.h                     from c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\bits\ios_base.h
42      c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\ios                     from c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\ios
38      c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\ostream                     from c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\ostream
39      c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\iostream                    from c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\iostream
1       C:\Users\r_bur_000\Documents\#PROGRAMS\Map_Generator\main.cpp                    from main.cpp
2793    5   c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\bits\basic_string.h    [Note] template<class _CharT, class _Traits, class _Alloc> std::basic_istream<_CharT, _Traits>& std::getline(std::basic_istream<_CharT, _Traits>&, std::basic_string<_CharT, _Traits, _Alloc>&)
2793    5   c:\program files (x86)\dev-cpp\mingw32\lib\gcc\mingw32\4.8.1\include\c++\bits\basic_string.h    [Note] template argument deduction/substitution failed:
117 15  C:\Users\r_bur_000\Documents\#PROGRAMS\Map_Generator\main.cpp   [Note] mismatched types 'std::basic_istream<_CharT, _Traits>' and 'std::ifstream* {aka std::basic_ifstream<char>*}'
28      C:\Users\r_bur_000\Documents\#PROGRAMS\Map_Generator\Makefile.win   recipe for target 'main.o' failed

Answer 1

你的問題在這里：

while(!house_files.eof())
{
    ifstream ifstr(path.c_str());      // 1
    houses.push_back(&ifstr);          // 2
    house_files >> path;
}

在行// 1 ，您在此 while 循環塊內的堆棧上聲明了一個ifstream對象。 這意味着在while循環結束后，該對象不再有效。

在第// 2行，您正在獲取該對象的地址，並將其放入您的向量中——希望在接下來的道路上，該地址將是有效的。 然而，正如我上面提到的，一旦你離開了 while 循環的范圍，它就不是了。

此外，您永遠不會為多個ifstream對象保留空間。 您只是不斷地重新初始化同一個對象，並將相同的（即將無效的）地址放入向量中。

你想做這樣的事情：

while(!house_files.eof())
{
    ifstream *ifstr = new ifstream(path.c_str());   // 1
    houses.push_back(ifstr);                        // 2
    house_files >> path;
}

使用new運算符在進程堆上為新的ifstream對象分配空間。 這個對象的地址存儲在ifstr指針中。 然后你可以把那個對象的地址放在你的向量中。

每當您使用new ，請記住您最終必須通過伴隨的delete釋放分配的內存。