c - 多线程程序中的段错误

Question

我已经声明了一个结构并尝试在主程序中使用该结构的元素。我不确定这是否是正确的方法。有什么替代方法吗？是否可以在 main 中声明新的矩阵和变量，然后将这些值分配给 struct 的值。我在结果矩阵的第一行中得到全 0，但第二行计算正确。另外，我应该动态创建线程吗？

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>

struct v {
int i; /* row */
 int j; /* column */
  int M, N, K;
float** A;
float** B;
float** C;
};


 void *runner(void *param); /* the thread */

  int main(int argc, char *argv[]) {

  int c, d, k, sum = 0;
 pthread_t tid[50];       //Thread ID
  int i,j, count = 0,thread_identifier,ret=5, count_dimension=0;
   char ch;
    struct v *data = (struct v *) malloc(sizeof(struct v));

    printf("Enter the number of rows and columns of first matrix\n");
    scanf("%d%d", &(data->M), &(data->K));
     (data->A) = malloc((data->M)*sizeof(float*));
     for ( i =0;i < data->M; i++)
 (data->A[i]) =malloc((data->K)*sizeof(float));

   printf("Enter the number of rows and columns of second matrix\n");
   (data->B) = malloc((data->K)*sizeof(float*));
   scanf("%d%d", &(data->K), &(data->N));
    for( i=0;i<(data->K);i++)
 (data->B[i]) = malloc((data->N)*sizeof(float));

     printf("Allocate memory for result matrix \n\n");
    (data->C) = malloc((data->M)*sizeof(float*));
     for( i=0;i<(data->M);i++)
     (data->C[i]) = malloc((data->N)*sizeof(float));

      printf("Enter the elements of first matrix\n");
      for( i = 0 ; i < data->M ; i++ )
       for ( j = 0 ; j < data->K ; j++ )
       scanf("%f", &(data->A[i][j]));

        printf("Enter the elements of second matrix\n");
        for( i = 0 ; i < data->K ; i++ )
         for ( j = 0 ; j < data->N ; j++ )
          scanf("%f", &(data->B[i][j]));



         for(i = 0; i < data->M; i++) 
  {
     j=0;

     data->i = i;
     data->j = j;
     /* Now create the thread passing it data as a parameter */

     pthread_attr_t attr; //Set of thread attributes
     //Get the default attributes
     pthread_attr_init(&attr);
     //Create the thread
     pthread_create(&tid[i],&attr,runner,data);
 //printf("create worker thread %u for row %d",(unsigned int)pthread_self(),i);
 printf("%lu",tid[i]);   
 printf("\n");
     count++;
 }  

   for(i=0;i< data->M;i++)
  {         

//Make sure the parent waits for all threads to complete
     pthread_join(tid[i], NULL);
   }      

   //Print out the resulting matrix
    for(i = 0; i < data->M; i++) {
    for(j = 0; j < data->N; j++) {
     printf("%.2e ", data->C[i][j]);
  }
printf("\n");

  }
  printf("\n"); 
  printf("%d",count);
 }

  //The thread will begin control in this function
   void *runner(void *param) {
   struct v *data = param; // the structure that holds our data
   int n,x=0, j=0; //the counter and sum
  float sum = 0.00;
   for(x=0;x<data->N;x++)
  {
for(j=0;j<data->N;j++)
{
    sum += data->A[data->i][j] * data->B[j][x];
}
data->C[data->i][x] = sum;
sum=0.00;
   }

  //Exit the thread
  //pthread_exit(0);
    }

Answer 1

*(data->A) = malloc((data->M)*sizeof(float*));

应该是

data->A = malloc((data->M)*sizeof(float*));

data->A 此时尚未初始化，因此取消引用它会调用未定义的行为。此外，它是一个float**，所以你想让它指向float*数组。

当然，data->B 也是如此。并且您还需要为data->C分配内存。