c++通过引用将映射传递给函数

c++ pass a map by reference into function

本文关键字：函数 映射 引用 c++      更新时间：2023-10-16

如何将map通过reference传递到函数中?Visual Studio 2010给了我一个unresolved externals错误。目前，我有以下简化的代码:

void function1(){
    map<int, int> * my_map = new map<int, int>(); 
    function2(*my_map); 
}
void function2(map<int, int> &temp_map){
    //do stuff with the map
}

这里有一些类似问题的答案，但他们利用typedef并将std::添加到定义的开头，但我真的不确定为什么。

int ComputerPlayer::getBestMoves(){
    //will return the pit number of the best possible move. 
    //map to hold pit numbers and rankings for each possible pit number.
    //map<pitNumber, rank> only adds pit numbers to map if they have seeds in them.
    std::map<int, int> possiblePits; //map
    std::map<int, int>::iterator it; //iterator for map
    for(int index = 1; index <= getBoardSize(); index++){
        if(_board.getPitValue(index) > 0){
            possiblePits.insert( pair<int, int>(index, 0) ); 
        }
    }
    int tempBoardSize = _board.getBoardSize();
    //loop that will analyze all possible pits in the map
    for(it = possiblePits.begin(); it != possiblePits.end(); it++){
        Board tempBoard = _board;
        int pitNum = it->first; 
        int score = analyzePlay(pitNum, tempBoard, possiblePits);
    }
    return 0; 
}
int analyzePlay(int pitNum, Board tempBoard, std::map<int, int> &possibleMoves){
    int tempBoardSize = tempBoard.getBoardSize(); 
    int tempSeeds = tempBoard.getPitValue(pitNum);
    int lastPitSown; 
    tempBoard.setPitToZero(pitNum); 
    for(int index = 1; index <= tempSeeds; index++){
        if(pitNum == tempBoardSize * 2 + 1){
            //skips over human's score pit 
            pitNum += 2; 
            lastPitSown = pitNum;
            tempBoard.incrementPit(pitNum);
        }
        else{
            pitNum++;
            lastPitSown = pitNum;
            tempBoard.incrementPit(pitNum);
        }
    }
    if(tempBoard.getPitValue(lastPitSown) == 1 && lastPitSown >= tempBoardSize + 2 && lastPitSown <= tempBoardSize * 2 + 1){
        //turn ends. last seed sown into empty pit on opponent side. 
    }
    else if(tempBoard.getPitValue(lastPitSown) > 1 && lastPitSown != tempBoardSize + 1){
        //keep playing with next pit. last seed was sown into non-empty pit. 
    }
    else if(lastPitSown == tempBoardSize + 1){
        //extra turn. last seed sown into score pit.
    }
    else if(tempBoard.getPitValue(lastPitSown) == 1 && lastPitSown != tempBoardSize + 1 && lastPitSown <= tempBoardSize && lastPitSown >= 1 ){
        //turn ends. last seed sown into empty pit on your side. capture.

    }
    return 0;
}

我得到的错误:

Error   1   error LNK2019: unresolved external symbol "public: int __thiscall ComputerPlayer::analyzePlay(int,class Board,class std::map<int,int,struct std::less<int>,class std::allocator<struct std::pair<int const ,int> > > &)" (?analyzePlay@ComputerPlayer@@QAEHHVBoard@@AAV?$map@HHU?$less@H@std@@V?$allocator@U?$pair@$$CBHH@std@@@2@@std@@@Z) referenced in function "public: int __thiscallComputerPlayer::getBestMoves(void)" (?getBestMoves@ComputerPlayer@@QAEHXZ)    C:UsersJoshDropboxCongkak_2Congkak_2ComputerPlayer.obj
Error   2   error LNK1120: 1 unresolved externals   C:UsersJoshDropboxCongkak_2DebugCongkak_2.exe

两件事:

  • 在顶部添加#include<map>，并使用std::map而不是map。
  • 将function2定义在function1之上，或者至少将function2声明在function1之上。

以下是如何做到这两点:

#include<map>
void function2(std::map<int, int> &temp_map); //forward declaration
void function1(){
    std::map<int, int>  my_map; //automatic variable 
                                //no need to make it pointer!
    function2(my_map); 
}
void function2(std::map<int, int> &temp_map){
    //do stuff with the map
}

还要注意尽可能避免使用new。默认情况下使用自动变量，除非您有非常强烈的理由不使用它。

自动变量很快，代码看起来整洁干净。有了它们，编写异常安全的代码就容易多了。

编辑:

现在当你发布错误时，你也意识到，

我忘记将函数所属的Class添加到它的开头。如:Player::function2(std::map<int,> &temp_map){}

，正如你在评论中所说的。

很好，你自己想出来了。但是，当你问问题时，总是在你的第一个帖子中发布错误。记住这一点。

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