c - 如何查找矩阵相乘的 C 程序中的错误

Question

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

struct ags{
    long int **mat1;
    long int **mat2;
    int *semafor;
    int rowsDone;
};

void *thread_multiply(void*);

int main(int args, char** argv){
    int mat1x;
    int mat1y;
    int mat2x;
    int mat2y;
    int threadsAmount;

    printf("Podaj szerokosc pierwszej macierzy: ");
    scanf("%i", &mat1x);
    printf("Podaj wysokosc pierwszej macierzy: ");
    scanf("%i", &mat1y);
    printf("Podaj szerokosc drugiej macierzy: ");
    scanf("%i", &mat2x);
    printf("Podaj wysokosc drugiej macierzy: ");
    scanf("%i", &mat2y);
    printf("Podaj ilosc watkow: ");
    scanf("%i", &threadsAmount);

    if(mat1x != mat2y){
        printf("Musisz podac odpowiednie macierze!");
        return;
    }

    struct ags* strAgs;

    int i;
    int j;
    for(i = 0; i < mat1y; i++){
        for(j = 0; j < mat1x; j++){
            strAgs->mat1[i][j] = random();
        }
    }

    for(i = 0; i < mat2y; i++){
        for(j = 0; j < mat2x; j++){
            strAgs->mat2[i][j] = random();
        }
    }


    for(j = 0; j < mat2x; j++){
        strAgs->semafor[j] = 0;
    }
    strAgs->rowsDone = mat2x;


    pthread_t threadsArray[threadsAmount];

    for(i = 0; i < threadsAmount; i++){
        if(pthread_create(&threadsArray[i], NULL, thread_multiply, (void*) strAgs)) {
        fprintf(stderr, "Error creating thread\n");
        return 1;
        } 
    }

    for(i = 0; i < threadsAmount; i++){
        if(pthread_join(threadsArray[i], NULL)) {
        fprintf(stderr, "Error joining thread\n");
        return 1;
        } 
    }
}

void *thread_multiply(void* ptr) {
    struct ags* agsStruct = (struct ags*) ptr;
    while(agsStruct->rowsDone > 0){
        printf("woho\n");
        agsStruct->rowsDone--;
    }
};

好的，这是代码。现在问题来了。我正在尝试编写一个程序来在线程中乘以矩阵。问题是我在尝试运行它时出现错误。它编译得很好，就在我开始输入 5 个整数时，它就崩溃了，我找不到原因。知道如何修复它吗？

Answer 1

您没有为矩阵分配内存。在您的 struct ags 结构中，您有两个 long** 条目，但您从未实际分配内存供它们使用。您需要使用 malloc 或 calloc 通过动态内存分配来完成此操作。

struct ags* strAgs;

错了。您正在创建一个指针，但没有将其指向任何数据。减少重写过多代码的快速解决方法是:

struct ags actualStruct;
struct ags* strAgs = &actualStruct;

您似乎正在尝试执行多线程矩阵乘法应用程序。我不会完成乘法逻辑，因为这看起来是家庭作业，但我在下面提供了代码的更新版本，它可以在 Linux 上编译和运行良好，并处理动态内存分配和取消分配/清理。 It also uses a constant MAX_VALUE to keep the matrix elements from suffering from integer overflow when your final program starts working.

祝你好运!

代码列表

<小时/>

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

#define MAX_VALUE (10)

struct ags{
   long int **mat1;
   long int **mat2;
   int *semafor;
   int rowsDone;
};

void *thread_multiply(void*);

int main(int args, char** argv){
   int mat1x;
   int mat1y;
   int mat2x;
   int mat2y;
   int threadsAmount;

   printf("Podaj szerokosc pierwszej macierzy: ");
   scanf("%i", &mat1x);
   printf("Podaj wysokosc pierwszej macierzy: ");
   scanf("%i", &mat1y);
   printf("Podaj szerokosc drugiej macierzy: ");
   scanf("%i", &mat2x);
   printf("Podaj wysokosc drugiej macierzy: ");
   scanf("%i", &mat2y);
   printf("Podaj ilosc watkow: ");
   scanf("%i", &threadsAmount);

   if(mat1x != mat2y){
      printf("Musisz podac odpowiednie macierze!");
      return;
   }
   struct ags actualStruct = { 0 };
   struct ags* strAgs = &actualStruct;

   int i;
   int j;
   printf("%d %d %d %d %d\n", mat1x, mat1y, mat2x, mat2y, threadsAmount);

   /* Dynamic memory allocation */
   int iErr = 0;
   if (!iErr) {
      if ((strAgs->mat1 = calloc(mat1y, sizeof(long int*))) == NULL) {
         printf("Memory allocation error!\n");
         iErr = 1;
      }
   }
   if (!iErr) {
      for (i=0; i<mat1y; i++) {
         if ((strAgs->mat1[i] = calloc(mat1x, sizeof(long int))) == NULL) {
            printf("Memory allocation error!\n");
            iErr = 1;
            break;
         }
      }
   }
   if (!iErr) {
      if ((strAgs->mat2 = calloc(mat2y, sizeof(long int*))) == NULL) {
         printf("Memory allocation error!\n");
         iErr = 1;
      }
   }
   if (!iErr) {
      for (i=0; i<mat2y; i++) {
         if ((strAgs->mat2[i] = calloc(mat2x, sizeof(long int))) == NULL) {
            printf("Memory allocation error!\n");
            iErr = 1;
            break;
         }
      }
   }
   if (!iErr) {
      if ((strAgs->semafor = calloc(mat2x, sizeof(int))) == NULL) {
         printf("Memory allocation error!\n");
         iErr = 1;
      }
   }

   /* Main logic */
   if (!iErr) {
      /* Populate the arrays */
      for(i = 0; i < mat1y; i++){
         for(j = 0; j < mat1x; j++){
            strAgs->mat1[i][j] = random() % MAX_VALUE;
         }
      }
      for(i = 0; i < mat2y; i++){
         for(j = 0; j < mat2x; j++){
            strAgs->mat2[i][j] = random() % MAX_VALUE;
         }
      }
      for(j = 0; j < mat2x; j++){
         strAgs->semafor[j] = 0;
      }
      strAgs->rowsDone = mat2x;

      /* Create group of worker threads to perform math operations */
      pthread_t threadsArray[threadsAmount];
      for(i = 0; i < threadsAmount; i++){
         if(pthread_create(&threadsArray[i], NULL, thread_multiply, (void*) strAgs)) {
            fprintf(stderr, "Error creating thread\n");
            return 1;
         }
      }

      /* Wait for all threads to complete before proceeding */
      for(i = 0; i < threadsAmount; i++){
         if(pthread_join(threadsArray[i], NULL)) {
            fprintf(stderr, "Error joining thread\n");
            return 1;
         }
      }

      /* Print out both matrices */
      printf("MATRIX 1:\n");
      for (i=0; i<mat1y; i++) {
         for (j=0; j<mat1x; j++) {
            printf("%02ld ", strAgs->mat1[i][j]);
         }
         printf("\n");
      }
      printf("MATRIX 2:\n");
      for (i=0; i<mat2y; i++) {
         for (j=0; j<mat2x; j++) {
            printf("%02ld ", strAgs->mat2[i][j]);
         }
         printf("\n");
      }
   }


   /* Clean up dynamically allocated memory */
   for (i=0; i<mat1y; i++) {
      free(strAgs->mat1[i]);
   }
   free(strAgs->mat1);

   for (i=0; i<mat2y; i++) {
      free(strAgs->mat2[i]);
   }
   free(strAgs->mat2);

   free(strAgs->semafor);

   /* Exit application */
   return 0;
}

void *thread_multiply(void* ptr) {
   struct ags* agsStruct = (struct ags*) ptr;
   while(agsStruct->rowsDone > 0){
      printf("woho\n");
      agsStruct->rowsDone--;
   }
};