[交流] 小白请各位大神帮我看看动态数组的问题已有1人参与

#include <cstdio>
#include <cstdlib>

int main(int argc, char **argv)
{
  int n, m;
  printf("Input n, m: ");
  scanf("%d %d", &n, &m);
  printf("Attempt to allocate %d bytes.\n", n*m*sizeof(double));
  double **ptr = (double **) malloc(n*sizeof(double *));
  double *data = (double *) malloc(n*m*sizeof(double));
  if (NULL == ptr || NULL == data) {
    printf("Memory allocation failed!\n");
    exit(EXIT_FAILURE);
  }
  for (int i = 0; i < n; i++)
    ptr[i] = data + i*m;
  printf("Set up matrix values.\n");
  for (int i = 0; i < n; i++)
    for (int j = 0; j < m; j++)
      ptr[i][j] = i*j;
  printf("Matrix:\n");
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < m; j++) {
      printf("%12.8g ", ptr[i][j]);
    }
    printf("\n");
  }
  printf("Deallocating matrix...\n");
  free(ptr);
  free(data);
  printf("Done\n");
  return 0;
}

2楼: Originally posted by 锐利的碎片 at 2014-05-30 18:31:51
你这样分配的内存不连续，会有些性能问题，一般都这样写：

#include <cstdio>
#include <cstdlib>

int main(int argc, char **argv)
{
  int n, m;
  printf("Input n, m: ";
   ...