局部变量可能指向释放的内存

Question

我在标头中有一个结构 (ex3.h)

typedef struct matrix {
    double **data;
    size_t n_rows;
    size_t n_columns;
} matrix;

在 c 文件中，我有函数“create_matrix”和另一个函数切片 我在某些地方收到警告“局部变量可能指向已释放的内存”。我在 cmets 中将它们标记为“--->”

#include <stdlib.h>
# include <stdio.h>
# include "ex3.h"
#define DEBUG
matrix *create_matrix (size_t n_rows, size_t n_columns)
{
  matrix *mat = malloc (sizeof (matrix));
  if (!mat)
    {
      fprintf (stderr, POINTER_ERROR);
      return NULL;
    }
  if (n_rows == ZERO || n_columns == ZERO)
    { mat->data = NULL, mat->n_rows = ZERO, mat->n_columns = ZERO; }
  else
    {
      {
        double **mat_data = malloc (n_rows * sizeof (double *));
        if (!mat_data)
          {
            free (mat);
            fprintf (stderr, POINTER_ERROR);
            return NULL;
          }
        for (int i = ZERO; i < n_rows; i++)
          {
            mat_data[i] = malloc (n_columns * sizeof (double));
            if (!mat_data[i])
              {
                for (int k = ZERO; k < i; k++)
                  {
                    free (mat_data[k]);
                  }
                free (mat_data), free (mat);
                fprintf (stderr, POINTER_ERROR);
                return NULL;
              }
            else
              {
                for (int j = ZERO; j < n_columns; j++)
                  {
                    mat_data[i][j] = (double) ZERO;

                  }
              }
          }
        mat->data = mat_data, mat->n_rows = n_rows, mat->n_columns = n_columns;

      }
    }
  return mat;
}

matrix *slice (matrix *mat, size_t row_start,
               size_t row_end, size_t col_start, size_t col_end)
{
 "some condions..."
    {
      matrix *m = create_matrix (ZERO, ZERO); //nul matrix
      if (!m) "<---"
        {
          return NULL;
        }
      return m; "<---"
    }
  else
    {
      size_t row = row_end - row_start, col = col_end - col_start;
      matrix *new_mat = create_matrix (row, col);
      if (!new_mat)"<---"
        {
          return NULL;
        }
      for (int i = ZERO; i < row; i++)
        {
          for (int j = ZERO; j < col; j++)
            {
           "--->"   (new_mat->data)[i][j] = mat->data[i + row_start][j + col_start];
            }
        }
      return new_mat; "<---"
    }
}

我做了一些条件来确保我不会尝试去内存空间中不属于我的矩阵的空间，那么为什么 clion 仍然发出警告 感谢您的帮助！

Answer 1

我会换一种方式。取而代之的是大量的分配，我只会使用一个。我会使用正面测试而不是负面测试（即有什么问题），并且该函数只有一个返回点。

typedef struct matrix {
    size_t n_rows;
    size_t n_columns;
    double data[];
} matrix;

matrix *allocate(size_t r, size_t c)
{
    matrix *m = malloc(sizeof(*m) + r * c * sizeof(m -> data[0]));
    if(m)
    {
        m -> n_rows = r;
        m -> n_columns = c;
    }
    return m;
}

matrix *slice(matrix *m, size_t sr, size_t er, size_t sc, size_t ec)
{
    matrix *result = NULL;
    size_t lc = ec - sc, lr = er - sr;
    if(m && m -> n_rows > er && m -> n_rows > sr && sr <= er && m -> n_columns > ec && m -> n_columns > sc && sc <= ec)
    {
        result = allocate(lr, lc);
        if(result)
        {
            double (*dest)[lc] = &result -> data;
            double (*src)[m -> n_columns] = &m -> data;

            result -> n_rows = lr;
            result -> n_columns = lc;
            for(size_t row = 0; row < lr; row ++)
            {
                memcpy(dest[row], &src[sr + row][sc], lc * sizeof(m -> data[0]));
            }
        }
    }
    return result;
}