c - C中的简单多线程错误？

Question

我是 C 语言的新手。我写了一段代码，它创建了两个线程来计算两个不同的结果。代码确实有效，但编译显示错误，我想知道实际上是什么错误。谁能帮我？我是 C 的新手，所以我想这可能是一个非常愚蠢的错误......

错误:

q3.c: In function ‘main’:
q3.c:63:2: warning: passing argument 3 of ‘pthread_create’ from incompatible pointer type [enabled by default]
In file included from q3.c:5:0:
/usr/include/pthread.h:225:12: note: expected ‘void * (*)(void *)’ but argument is of type ‘double * (*)(void *)’
q3.c:64:9: warning: passing argument 3 of ‘pthread_create’ from incompatible pointer type [enabled by default]
In file included from q3.c:5:0:
/usr/include/pthread.h:225:12: note: expected ‘void * (*)(void *)’ but argument is of type ‘double * (*)(void *)’

代码:

#include <stdlib.h>
#include <pthread.h>
#include <string.h>
#include<stdio.h>
#include<math.h>
#define PI 3.1415

int i, x, n;

double *sin_x(void* dimension);
double *cos_x(void* dimension);
int fact(int);
struct data
{
  int ang_deg;
  int no_of_terms;
};

int fact(int num)
{
  int f = 0;

  if (num == 1)
    return 1;
  else
    f = num * fact(num - 1);

  return f;
}

int main(int argc, char argv[])
{
  printf("\nEnter x and n:\t");
  scanf("%d %d", &x, &n);

  struct data
  {
    int ang_rad;
    int no_of_terms;
  };

  struct data dimension;  // automatic allocation, all fields placed on stack

  dimension.ang_rad = x;
  dimension.no_of_terms = n;

  pthread_t thrd1, thrd2;
  int thret1, thret2;

  thret1 = pthread_create(&thrd1, NULL, sin_x, (void *) &dimension);
  thret2 = pthread_create(&thrd2, NULL, cos_x, (void *) &dimension);

  pthread_join(thrd1, NULL );
  pthread_join(thrd2, NULL );

  //printf("\nthret1 = %d\n", thret1);
  //printf("thret2 = %d\n", thret2);
  sleep(5);
  printf("Parent Thread exiting...\n");

  exit(1);

  return 0;
}

double *sin_x(void* dimension)
{
  struct data* dim = (struct data*) dimension;
  int ang_deg = dim->ang_deg;
  int no_of_terms = dim->no_of_terms;

  //int ang_deg, int no_of_terms
  int term, j;
  double value = 0.0, ang_rad = 0.0;
  ang_rad = (double) ang_deg * PI / 180;

  for (term = 1, j = 2; term < no_of_terms * 2; term += 2, j++)
  {
    value += (double) pow(-1.0, j) * pow(ang_rad, term) / fact(term);
  }

  printf("\nSin(%d) = %f", ang_deg, value);
  double *a = &value;

  return a;
}

double *cos_x(void* dimension)
{
  struct data* dim = (struct data*) dimension;
  int ang_deg = dim->ang_deg;
  int no_of_terms = dim->no_of_terms;

  int term, j;
  double value = 1.0, ang_rad = 0.0;
  ang_rad = (double) ang_deg * PI / 180;

  for (term = 2, j = 1; term <= no_of_terms; term += 2, j++)
  {
    value += (double) pow(-1.0, j) * pow(ang_rad, term) / fact(term);
  }

  printf("\nCos(%d) = %f", ang_deg, value);
  double *a = &value;

  return a;
}

Answer 1

这不是错误，而是警告。

你的功能是:

double *sin_x (void *dimension);double *cos_x (void *dimension);

因为函数名是指向函数的指针，sin_x 的类型是:double * (*) (void *)以 void* 作为参数并返回 double * 的函数)，与 cos_x 相同。

但是 pthread_create 正在等待 void * (*) (void *) 类型(指向以 void* 作为函数的指针参数并返回 void*)。

由于 double* 和 void* 都是指针，它们具有相同的大小(例如 64b 上的 8 个字节)，因此编译器只会警告您。