如何通过 reference
将 map
传递给函数? Visual Studio 2010 给了我一个 unresolved externals
错误。目前,我有以下简化代码:
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,但他们使用 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:\Users\Josh\Dropbox\Congkak_2\Congkak_2\ComputerPlayer.obj
Error 2 error LNK1120: 1 unresolved externals C:\Users\Josh\Dropbox\Congkak_2\Debug\Congkak_2.exe
最佳答案
两件事:
- 添加
#include<map>
在顶部,并使用std::map
而不仅仅是map
. - 定义
function2
以上function1
或者至少声明function2
以上function1
.
这两种方法都应该这样做:
#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
}
还要注意避免new
越多越好。默认情况下使用自动变量,除非你有很强的理由不使用它。
自动变量速度很快,代码看起来整洁干净。使用它们可以更轻松地编写异常安全代码。
编辑:
现在,当您发布错误时,您也意识到,
I forgot to add the Class that the function was part of to the beginning of it. as in: Player::function2(std::map<int, int> &temp_map){}
,正如你在评论中所说。
很好,你自己想通了。但是,当您提出问题时,请始终在您的第一篇文章中发布错误。记住这一点。
关于c++通过引用将映射传递给函数,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/7763397/