如何解决如何重新分配三重指针
我目前正在为用C ++实现的tictactoe的ai进行开发,目前我的进展正在进行中。在我的代码中,我有一个看起来像这样的结构。
struct Board {
int config[3][3];
Board ** nextboards;
};
我将nextboards设为了双指针,因为我想动态地将一个木板分配给未知数目的木板。使用指针数组将使我的存储不动态。为了增加可能的动作,我做了一个功能。
void addPossibleMoves(Board *** board,bool xplayer) {
Board * newboard = (Board *)malloc(sizeof(Board));
Board * another = (Board *)malloc(sizeof(Board));
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
newboard -> config[i][j] = compare[i][j];
}
}
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
another -> config[i][j] = compare[i][j];
}
}
Board ***temp = (Board ***)realloc(board,2*sizeof(Board));
temp = board;
**board = newboard;
printBoard( **board);
}
在此函数中,我通过引用传入双指针以操纵内部数据。我的目的是为**board
重新分配两倍的大小,并插入两个节点以测试其是否有效。但是,当代码运行realloc函数时,它将暂停并返回不为零的值。有人可以告诉我我在做什么错。
这是我的主要功能。
int main() {
bool xplayer = true;
Board * startboard = (Board *)malloc(sizeof(Board));
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
startboard -> config[i][j] = compare[i][j];
}
}
startboard -> nextboards = (Board **)malloc(sizeof(Board));
addPossibleMoves( & startboard -> nextboards,xplayer);
printBoard( *(startboard -> nextboards));
}
我目前正在使用devc ++作为我的助手。
解决方法
我按照我认为的样子重写了您的代码。我完全保留了您应该执行什么代码的逻辑。另外,我还保留了您的malloc
/ realloc
/ free
低级别的内存处理方式。我的代码仍然具有此三重指针***
,向您展示如何使用它。另外,在使用free
分配之后,您忘记了malloc
的所有内存,您应该始终释放分配的那些指针!
在真正的C ++代码中,您应该使用new
/ delete
/ delete[]
而不是malloc / free。我认为,甚至使用new
/ delete
都不是一个好习惯,最好使用那些已经为您完成所有内存管理的结构,例如std::vector,请参阅第二篇。这样的示例的解决方案,与其保留普通指针并手动删除它们,不如使用std::shared_ptr之类的智能指针。
第一个代码基本上是您的代码,但有所改进。
#include <cstdlib>
#include <cstdio>
struct Board {
int config[3][3];
Board ** nextboards;
};
void freeNextBoards(Board ** nextboards) {
Board ** cur = nextboards;
while (*cur) {
freeNextBoards((*cur)->nextboards);
++cur;
}
nextboards[0] = 0;
}
void freeBoard(Board * board) {
freeNextBoards(board->nextboards);
}
void resizeNextBoards(Board *** pnextboards,int cnt) {
*pnextboards = (Board **)realloc(*pnextboards,cnt * sizeof(Board*));
}
Board * createBoard() {
Board * board = (Board *)malloc(sizeof(Board));
board->nextboards = (Board **)malloc(1 * sizeof(Board*));
board->nextboards[0] = 0;
return board;
}
void printRepStr(char const * s,int cnt = 1) {
for (int j = 0; j < cnt; ++j)
printf("%s",s);
}
void printBoard(Board * board,int indent = 0) {
for (int i = 0; i < 3; ++i) {
printRepStr(" ",indent);
for (int j = 0; j < 3; ++j)
printf("%02d ",board->config[i][j]);
printf("\n");
}
printRepStr(" ",indent);
printRepStr("-",3 * 3 - 1);
printf("\n");
Board ** cur = board->nextboards;
while (*cur) {
printBoard(*cur,indent + 4);
++cur;
}
}
void addPossibleMoves(Board *** pnextboards,bool xplayer) {
Board * newboard = createBoard();
Board * another = createBoard();
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
newboard->config[i][j] = 2 * (i + j); // compare[i][j];
}
}
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
another->config[i][j] = 3 * (i + j); // compare[i][j];
}
}
freeNextBoards(*pnextboards);
resizeNextBoards(pnextboards,3);
(*pnextboards)[0] = newboard;
(*pnextboards)[1] = another;
(*pnextboards)[2] = 0;
}
int main() {
bool xplayer = true;
Board * startboard = createBoard();
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
startboard->config[i][j] = 1 * (i + j); // compare[i][j];
}
}
addPossibleMoves(&startboard->nextboards,xplayer);
addPossibleMoves(&startboard->nextboards[0]->nextboards,xplayer);
printBoard(startboard);
freeBoard(startboard);
return 0;
}
输出:
00 01 02
01 02 03
02 03 04
--------
00 02 04
02 04 06
04 06 08
--------
00 02 04
02 04 06
04 06 08
--------
00 03 06
03 06 09
06 09 12
--------
00 03 06
03 06 09
06 09 12
--------
下面的 第二个代码是第一个代码的改进版本,现在代替了我使用std::vector
自动管理内存的所有地方的指针,我使用的config
的普通2D数组std::array,为了将文本输出到控制台,我使用了std::cout,也为了捕获异常,我使用了try
/ catch
和std::exception。
您可以看到,在下面的基于矢量的代码中,您根本不需要使用malloc
/ realloc
/ free
做任何工作,因为您始终会忘记释放分配后,一切都会在vector的代码内自动完成。
#include <cstdlib>
#include <cstdio>
#include <vector>
#include <array>
#include <stdexcept>
#include <iostream>
#include <iomanip>
using namespace std;
struct Board {
array<array<int,3>,3> config = {};
vector<Board> nextboards;
};
void printRepStr(char const * s,size_t cnt = 1) {
for (size_t j = 0; j < cnt; ++j)
cout << s;
}
void printBoard(Board const & board,size_t indent = 0) {
for (size_t i = 0; i < board.config.size(); ++i) {
printRepStr(" ",indent);
for (int j = 0; j < board.config[i].size(); ++j)
cout << setfill(' ') << setw(2) << board.config[i][j] << " ";
cout << endl;
}
printRepStr(" ",board.config[0].size() * 3 - 1);
cout << endl;
for (auto const & cur: board.nextboards)
printBoard(cur,indent + 4);
}
void addPossibleMoves(vector<Board> & pnextboards,bool xplayer) {
Board newboard,another;
for (size_t i = 0; i < newboard.config.size(); ++i)
for (int j = 0; j < newboard.config[i].size(); ++j)
newboard.config[i][j] = 2 * (i + j); // compare[i][j];
for (size_t i = 0; i < another.config.size(); ++i)
for (int j = 0; j < another.config[i].size(); ++j)
another.config[i][j] = 3 * (i + j); // compare[i][j];
pnextboards.resize(2);
pnextboards[0] = newboard;
pnextboards[1] = another;
}
int main() {
try {
bool xplayer = true;
Board startboard;
for (size_t i = 0; i < startboard.config.size(); ++i)
for (size_t j = 0; j < startboard.config[i].size(); ++j)
startboard.config[i][j] = 1 * (i + j); // compare[i][j];
addPossibleMoves(startboard.nextboards,xplayer);
addPossibleMoves(startboard.nextboards[0].nextboards,xplayer);
printBoard(startboard);
return 0;
} catch (exception const & ex) {
cout << "Exception: " << ex.what() << endl;
} catch (...) {
cout << "Unknown Exception!" << endl;
}
}
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