c - 从 ‘int*’ 到 ‘unsigned int*’ 的无效转换 [-fpermissive]

Question

我的老师给了我这段应该可以编译的代码。它应该通过使用线程来计算 PI。然后我们应该对程序进行计时和/或向代码添加适当的计时系统调用。运行不同的线程并创建一个比较时间和线程数量的图...问题是，我不知道如何解决这个问题。我从未处理过这样的事情，也没有自己构建代码，所以我对如何修复它感到困惑。

编译器说问题来自:

rand_no_y = (double) (rand_r( &seed ))/(double)RAND_MAX;
                                       ^

和

rand_no_x = (double) (rand_r( &seed ))/(double)RAND_MAX;

完整代码如下:

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


#define MAX_THREADS 512

void *compute_pi( void * );


//int sample_points;
int total_hits;
int total_misses;
int hits[ MAX_THREADS ];
int sample_points;
int sample_points_per_thread;
int num_threads;



int main( int argc, char *argv[] )
{
  /* local variables */
  int ii;
  int retval;
  pthread_t p_threads[MAX_THREADS];
  pthread_attr_t attr;
  double computed_pi;

  /* initialize local variables */
  retval = 0;


  pthread_attr_init( &attr );
  pthread_attr_setscope( &attr, PTHREAD_SCOPE_SYSTEM );

  /* parse command line arguments into sample points and number of threads */
  /* there is no error checking here!!!!! */
  sample_points = atoi(argv[1]);
  num_threads = atoi(argv[2]);

  /* uncomment this block if you want interactive input!!!! */
  /* if so...comment out the two statements above */
  /*  
  printf( "Enter number of sample points: " );
  scanf( "%d", &sample_points );
  printf( "Enter number of threads: " );
  scanf( "%d%", &num_threads );
  */

  total_hits = 0;
  sample_points_per_thread = sample_points / num_threads;

  for( ii=0; ii<num_threads; ii++ )
    {
      hits[ii] = ii;
      pthread_create( &p_threads[ ii ], &attr, compute_pi, (void *) &hits[ii] );
    }

  for( ii=0; ii<num_threads; ii++ )
    {
       pthread_join( p_threads[ ii ], NULL );
       total_hits += hits[ ii ];
    }

   computed_pi = 4.0 * (double) total_hits / ((double) (sample_points));


   printf( "Computed PI = %lf\n", computed_pi );


  /* return to calling environment */
  return( retval );
}


void *compute_pi( void *s )
{
  int seed;
  int ii;
  int *hit_pointer;
  int local_hits;
  double rand_no_x;
  double rand_no_y;

  hit_pointer = (int *) s;
  seed = *hit_pointer;
  local_hits = 0;

  for( ii=0; ii < sample_points_per_thread; ii++ )
    {
      rand_no_x = (double) (rand_r( &seed ))/(double)RAND_MAX;

      rand_no_y = (double) (rand_r( &seed ))/(double)RAND_MAX;

      if(((rand_no_x - 0.5) * (rand_no_x - 0.5) +
      (rand_no_y - 0.5) * (rand_no_y - 0.5)) < 0.25)

    local_hits++;

      seed *= ii;
    }

  *hit_pointer = local_hits;
  pthread_exit(0);
}

Answer 1

对于int seed，&seed是一个int *。

rand_r(unsigned int *seedp)需要一个无符号*

对 seed、ii 和其他使用 unsigned，