在C ++中动态2D字符串数组的重新分配

Question

I'm having trouble understanding why my delete method is incorrect.

For my matrix creation I have:

 43    matrix = new string*[row];
 44    for(int i = 0; i < row; i++) {
 45       matrix[i] = new string[col];
 46    }
 47    for(int i = 0; i < row; i++) {
 48       for(int j = 0; j < col; j++) {
 49          matrix[i][j] = array[i][j];
 50          //cout << matrix[i][j] << ' ';
 51       }
 52       cout << endl;
 53    }

Then in my destructor I have:

 15    for(int i = 0; i < row; i++) {
 16       delete matrix[i];
 17    }
 18    delete matrix;

My program crashes on the first entry of deletion

Answer 1

As already stated, you must pair new[] with delete[] . In these lines:

matrix = new string*[row];
matrix[i] = new string[col];

You use new[] , therefore later on, you must do:

delete[] matrix[i];
delete[] matrix;

For reference, see this link .

When you allocated your two-dimensional array, you really created N one-dimensional arrays. Now each of those have to be deleted, but the system does not know how many of them there are. The size of the top-level array, ie the array of pointers to your second-level arrays, is just like any other array in C: its size is not stored by the system.

Here's what valgrind has to say if you use delete instead of delete [] :

==30045== Mismatched free() / delete / delete []
==30045==    at 0x4A05FD6: operator delete(void*) (vg_replace_malloc.c:480)
==30045==    by 0x400725: main
==30045==  Address 0x4c2e040 is 0 bytes inside a block of size 160 alloc'd
==30045==    at 0x4A07152: operator new[](unsigned long) (vg_replace_malloc.c:363)
==30045==    by 0x400715: main

Answer 2

 matrix = new string*[row];
 for(int i = 0; i < row; i++) {
    matrix[i] =delete[col];
 }
delete[] matrix;