Question

有人可以告诉我此代码段的描述吗？

chessBoard = new char*[ tRows ] ;
for ( unsigned int c = 0; c < rows; c++ )
{
    chessBoard[ c ] = new char[ columns ];
}

问题：

char*[tRows]是什么，其作用是什么？
而且，chessBoard[c]是什么？

请给我准确的描述。

Answer 1

char *chessBoard  = new char[ tRows ] ; //correct definition
//chessBoard is a pointer to array of tRow size of characters

for( unsigned int c = 0 ;   c < rows ;   c++ )
chessBoard[ c ] = new char[ columns ] ;
//we assign each row with a constant number of columns

您已经知道，棋盘基本上可以表示为方阵，因此

Matrix dimension: Row x Column where Row = Column

希望能回答您的问题！

干杯

Arul Verman

Answer 2

虽然您可以自由声明和分配指向char [tRows]的指针数组，然后循环分配每一行，但您也可以声明指向char数组的指针[ [tRows] 并在单个调用中分配其中tRows个，这提供了单个分配和单个空闲的好处，例如

#include <iostream> #include <iomanip> #define tRows 10 int main (void) { char (*chessboard)[tRows] = new char[tRows][tRows]; for (int i = 0; i < tRows; i++) { for (int j = 0; j < tRows; j++) { chessboard[i][j] = i + j; std::cout << " " << std::setw(2) << (int)chessboard[i][j]; } std::cout << '\n'; } delete[] (chessboard); }

使用/输出示例

$ ./bin/newdelete2d 0 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 10 2 3 4 5 6 7 8 9 10 11 3 4 5 6 7 8 9 10 11 12 4 5 6 7 8 9 10 11 12 13 5 6 7 8 9 10 11 12 13 14 6 7 8 9 10 11 12 13 14 15 7 8 9 10 11 12 13 14 15 16 8 9 10 11 12 13 14 15 16 17 9 10 11 12 13 14 15 16 17 18

，然后确认您的内存使用情况：

$ valgrind ./bin/newdelete2d ==7838== Memcheck, a memory error detector ==7838== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al. ==7838== Using Valgrind-3.12.0 and LibVEX; rerun with -h for copyright info ==7838== Command: ./bin/newdelete2d ==7838== 0 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 10 2 3 4 5 6 7 8 9 10 11 3 4 5 6 7 8 9 10 11 12 4 5 6 7 8 9 10 11 12 13 5 6 7 8 9 10 11 12 13 14 6 7 8 9 10 11 12 13 14 15 7 8 9 10 11 12 13 14 15 16 8 9 10 11 12 13 14 15 16 17 9 10 11 12 13 14 15 16 17 18 ==7838== ==7838== HEAP SUMMARY: ==7838== in use at exit: 0 bytes in 0 blocks ==7838== total heap usage: 2 allocs, 2 frees, 72,804 bytes allocated ==7838== ==7838== All heap blocks were freed -- no leaks are possible ==7838== ==7838== For counts of detected and suppressed errors, rerun with: -v ==7838== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

二维阵列的动态分配

2 个答案: