在C ++中的2D动态内存分配数组中自由分配内存 [英] free allocated memory in 2D dynamic memory allocation array in C++

问题描述

我最近发布了一个有关这个问题，但这是一个不同的问题。我使用动态内存分配创建了一个二维数组，使用矩阵后，我们需要通过删除它释放内存，我不明白为什么我们不能只使用 delete [] matrix

  int ** matrix; 
 
 //动态分配数组
 matrix = new int * [row]; 
 for（int count = 0; count< row; count ++）
 matrix [count] = new int [col] 
 
 //自由动态分配的内存
 for（int i = 0; i <* row; i ++）
 {
 delete [] matrix [i] 
 delete [] matrix;因为问题是因为在 main（）     / code>我创建了一个二维数组并使用其他 int ** 函数分配值，我不知道如何删除分配的内存，循环将导致运行时错误
  int main（）
 {
 int ** matrixA = 0，** matrixB = 0 ，** matrixResult = 0; //动态分配数组
 int rowA，colA，rowB，colB; //保存矩阵的大小
 
 //获取输入法的值
 int inputMethod = userChoiceOfInput（）; 
 if（inputMethod == 1）//通过键盘选择输入
 {
 cout< 矩阵A输入... \\\
; 
 matrixA = getMatricesByKeyboard（& rowA，& colA）; 
 cout<< 矩阵B输入... \\\
; 
 matrixB = getMatricesByKeyboard（& rowB，& colB）; 
} 
 else if（inputMethod == 2）//通过文件选择输入
 {
 matrixA = getMatricesByFileInput（F：\\matrixA.txt，& rowA，& colA）; 
 matrixB = getMatricesByFileInput（F：\\matrixB.txt，& rowB，& colB）; 
} 
 
 //添加（matrixA，& rowA，& colA，matrixB，& rowB，& colB）; 
 
 cout<< matrixA [1] [0]; 
 
 ////////////////////////运行时错误/////////////// //////// 
 //自由分配的矩阵A的内存
 for（int i = 0; i  {
 delete [] matrixA [i]; 
 delete [] matrixA; 
} 
 //矩阵B的空闲分配内存
 for（int i = 0; i  {
 delete [] matrixB [i ]; 
 delete [] matrixB; 
} 
 ////////////////////////运行时错误////////////// ///////// 
 
 //矩阵A的空闲分配内存
 delete [] matrixA; //我不知道什么会这些删除
 delete [] matrixB; 
 
 return 0; 
} 
  
 
 
解决方案
矩阵并删除每个数组。在这样做的最后，你可以删除矩阵本身
  //自由动态分配内存
 for = 0; i <* row; i ++）
 {
 delete [] matrix [i] //删除矩阵中的数组
} 
 //删除实际矩阵
 delete [] matrix; 
  
 
I recently posted a question about this, but this is a different question. I created a 2D arrays using dynamic memory allocation, after the matrix is used, we need to free the memory by delete it and I dont understand why we cant just use delete [] matrix to delete it instead of the method in the codes below
int **matrix;

    // dynamically allocate an array
    matrix = new int *[row]; 
    for (int count = 0; count < row; count++)
        matrix[count] = new int[col];

    // free dynamically allocated memory
    for( int i = 0 ; i < *row ; i++ )
    {
        delete [] matrix[i] ;
        delete [] matrix ;
    }
Because the problem is because in main() i created a 2D array and assign the values using other int ** functions, i dont know how to delete the allocated memory, the loop will cause runtime error
    int main()
    {
        int **matrixA = 0, **matrixB = 0, **matrixResult = 0; // dynamically allocate an array
        int rowA, colA, rowB, colB; // to hold the sizes of the matrices

        // get values for input method
        int inputMethod = userChoiceOfInput();
        if (inputMethod == 1) // select input by keyboard
        {
            cout << "Matrix A inputting...\n";
            matrixA = getMatricesByKeyboard(&rowA, &colA);
            cout << "Matrix B inputting...\n";
            matrixB = getMatricesByKeyboard(&rowB, &colB);
        }
        else if (inputMethod == 2) // select input by files
        {
            matrixA = getMatricesByFileInput("F:\\matrixA.txt", &rowA, &colA); 
            matrixB = getMatricesByFileInput("F:\\matrixB.txt", &rowB, &colB); 
        }

        //addition(matrixA, &rowA, &colA, matrixB, &rowB, &colB);

        cout << matrixA[1][0];  

////////////////////////run time error///////////////////////
    // free allocated memory of matrix A
    for( int i = 0 ; i < rowA ; i++ )
    {
        delete [] matrixA[i] ;
        delete [] matrixA ;
    }
    // free allocated memory of matrix B
    for( int i = 0 ; i < rowB ; i++ )
    {
        delete [] matrixB[i] ;
        delete [] matrixB ;
    }
////////////////////////run time error///////////////////////

        // free allocated memory of matrix A
        delete [] matrixA ; // i dont know what would these delete
        delete [] matrixB ; 

        return 0;
    }

解决方案
You have to go through your matrix and delete each array. At the end of doing that you can delete the matrix itself
// free dynamically allocated memory
for( int i = 0 ; i < *row ; i++ )
{
    delete[] matrix[i]; // delete array within matrix
}
// delete actual matrix
delete[] matrix;


                        
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