c - 多线程数据处理，如果多两个 argvs 总是会出现错误

Question

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

typedef struct {
   int id;
   char *filename;
   float sum;
   float dif;
} child;

void *calData(void *argv){

   child *tempChild = (child *) argv;
   FILE *fp;
   int id = tempChild->id;
   float max, min,buffer, sum , dif;

   if(fopen(tempChild->filename, "r") == NULL) {
       printf("Fail to open file");
       exit(1);
   }
   fp = fopen(tempChild->filename, "r");
   fscanf(fp, "%f", &buffer);
   /* initialize the max and min */
   max = buffer;
   min = buffer;
   /* scan every element in the dataset */
   while(!feof(fp)) {
       fscanf(fp, "%f", &buffer);
       if(buffer <= min) {
           min = buffer;
       }  
       if(buffer >= max) {
           max = buffer;
       }
   }
   fclose(fp);  
   /* pass the calculted results to child */
   sum = max + min;
   dif = max - min;

   tempChild->sum = sum;
   tempChild->dif = dif;
   printf("%.5f  %.5f %.5f\n", sum, dif, id);
  }

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

     /* initialize the of memory size of threads and children */
     pthread_t *threads;
     threads = (pthread_t *) malloc((argc-1) * sizeof(*threads));
     child *children;
     children = (child *) malloc((sizeof(child)) * (argc - 1));
     int i, j;

     /* start the threads */
     for(i=0; i < (argc - 1); i++)
     {
          children[i].id = i;
          children[i].filename = argv[i+1];
          pthread_create(threads+i, NULL, calData, (void *)children+i);
     }
    /* Synchronize the completion of each thread. */
    for(j=0; j < (argc-1); j++){
       pthread_join(threads[j], NULL);
    }
    printf("%.5f  %.5f \n",children[0].sum, children[0].dif);
 }

你好，我正在学习 pthread。 这是问题，正如您可能在代码中看到的那样，输入应包含 3 个 txt 文件，我想处理它们并通过 pthread 获取 sum 和 dif。然而，一个输入参数没问题，但当我尝试输入 3 个数据文件时，它一直说“无法打开文件”。

我搜索过我可能需要一些有关互斥锁的帮助，谁能告诉我如何解决它？

Answer 1

这是明显的第一个问题:

pthread_create(threads+i, NULL, calData, (void *)children+i);

检查 C 中的操作优先级并将其替换为:

pthread_create(threads+i, NULL, calData, (void *)(children + i));

您的地址算术 + 运算符的优先级低于 (void *) 类型转换，因此 children 递增 i 字节而不是 i child 结构大小。

但实际上，如果您的 C 编译器允许，我确实建议在您的情况下从指针切换到数组。更安全所以这是你的 main():

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

     pthread_t threads[argc -1];
     child children[argc - 1];

     int i, j;

     /* start the threads */
     for(i=0; i < (argc - 1); i++)
     {
          children[i].id = i;
          children[i].filename = argv[i+1];
          pthread_create(&threads[i], NULL, calData, &children[i]);
     }

    /* Synchronize the completion of each thread. */
    for(j=0; j < (argc-1); j++){
       pthread_join(threads[j], NULL);
    }
    printf("%.5f  %.5f \n",children[0].sum, children[0].dif);
}