[英]C++ cout prints entire contents of 2D char array
我正在寫一個井字游戲來學習 C++。
我想將游戲板存儲在 2D 字符數組中:
char playerBoard[5][14] {
{'2',' ','>',' ','_',' ','|',' ','_',' ','|',' ','_','\n'},
{'1',' ','>',' ','_',' ','|',' ','_',' ','|',' ','_','\n'},
{'0',' ','>',' ','_',' ','|',' ','_',' ','|',' ','_','\n'},
{' ',' ',' ',' ','^',' ',' ',' ','^',' ',' ',' ','^','\n'},
{' ',' ',' ',' ','0',' ',' ',' ','1',' ',' ',' ','2','\n'}
};
我想用 cout 打印數組:
for (int i = 0; i < 5; i++) {
cout << playerBoard[i];
}
當我嘗試時,從第一個數組開始的playerboard
的全部內容在每次迭代時都會打印出來:
2 > _ | _ | _
1 > _ | _ | _
0 > _ | _ | _
^ ^ ^
0 1 2
1 > _ | _ | _
0 > _ | _ | _
^ ^ ^
0 1 2
0 > _ | _ | _
^ ^ ^
0 1 2
^ ^ ^
0 1 2
0 1 2
playerBoard 的全部內容打印為:
cout << playerBoard[0];
這里發生了什么?
您的五個數組子元素都不是以nul
結尾的字符串(可能最后一個除外,但這依賴於未定義的行為)。
帶有char*
操作數(或char[]
操作數,衰減為char*
)的std::cout <<
操作假定以nul
結尾的字符串; 在您的情況下,由於缺少終止符,因此會打印緩沖區,直到在某處找到一個為止。 這似乎是在整個數組塊之后。
要解決此問題,請將子數組的大小增加到 15 個字符並添加所需的nul
(零)終止符:
int main()
{
char playerBoard[5][15]{
{'2',' ','>',' ','_',' ','|',' ','_',' ','|',' ','_','\n','\0'},
{'1',' ','>',' ','_',' ','|',' ','_',' ','|',' ','_','\n','\0'},
{'0',' ','>',' ','_',' ','|',' ','_',' ','|',' ','_','\n','\0'},
{' ',' ',' ',' ','^',' ',' ',' ','^',' ',' ',' ','^','\n','\0'},
{' ',' ',' ',' ','0',' ',' ',' ','1',' ',' ',' ','2','\n','\0'}
};
for (int i = 0; i < 5; i++) {
std::cout << playerBoard[i];
}
return 0;
}
你有未定義的行為,因為std::cout << playerBoard[i];
期望playerBoard[i]
是(指向第一個元素的) null 終止數組,並且沒有 null 字符( char{0}
)。
要解決此問題,請使用適用於非空終止字符 arrays std::cout.write(s, count)
或std::string_view
string_view:
for (int i = 0; i < 5; i++) {
std::cout.write(playerBoard[i], std::size(playerBoard[i]));
// Or
std::cout << std::string_view(playerBoard[i], std::size(playerBoard[i]));
}
或者,在末尾添加一個 null 終止符:
char playerBoard[][14] {
{'2',' ','>',' ','_',' ','|',' ','_',' ','|',' ','_','\n'},
{'1',' ','>',' ','_',' ','|',' ','_',' ','|',' ','_','\n'},
{'0',' ','>',' ','_',' ','|',' ','_',' ','|',' ','_','\n'},
{' ',' ',' ',' ','^',' ',' ',' ','^',' ',' ',' ','^','\n'},
{' ',' ',' ',' ','0',' ',' ',' ','1',' ',' ',' ','2','\n'},
{0}
};
// Print the whole array
std::cout << *playerBoard;
// (You can still print individual lines the same way like as above)
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