0

我有以下代码用于使用 pthreads 计算 n-queen 谜题。但是当我尝试编译该代码时，我收到以下错误消息：

wikithread.c:7:5：错误：在文件范围内可变地修改了“hist”

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

int NTHREADS, SIZE; 
int hist[SIZE];
int count = 0;

int solve(int col, int tid)
{
    int start = tid * SIZE/NTHREADS;
    int end = (tid+1) * (SIZE/NTHREADS) - 1;
    int i, j;
    if (col == SIZE) 
    {
        count++;
    }

    #define attack(i, j) (hist[j] == i || abs(hist[j] - i) == col - j)
    for (i = start; i <= end; i++) {
        for (j = 0; j < col && !attack(i, j); j++);
        if (j < col) continue;

        hist[col] = i;
        solve(col + 1, tid);
    }

    return count;
}

void *worker(void *arg)
{
    int tid = (int)arg;
    solve(0, tid);
}

int main(int argc, char* argv[])
{
    pthread_t* threads;
    int rc, i;

    // checking whether user has provided the needed arguments
    if(argc != 3)
    {
        printf("Usage: %s <number_of_queens> <number_of_threads>\n", argv[0]);
        exit(1);
    }


    // passing the provided arguments to the SIZE and NTHREADS 
    // variable, initializing matrices, and allocating space 
    // for the threads
    SIZE = atoi(argv[1]);
    NTHREADS = atoi(argv[2]);
    threads = (pthread_t*)malloc(NTHREADS * sizeof(pthread_t));

    // declaring the needed variables for calculating the running time
    struct timespec begin, end;
    double time_spent;

    // starting the run time
    clock_gettime(CLOCK_MONOTONIC, &begin);

    for(i = 0; i < NTHREADS; i++) {
        rc = pthread_create(&threads[i], NULL, worker, (void *)i);
        assert(rc == 0); // checking whether thread creating was successfull
    }

    for(i = 0; i < NTHREADS; i++) {
        rc = pthread_join(threads[i], NULL);
        assert(rc == 0); // checking whether thread join was successfull
    }

    // ending the run time
    clock_gettime(CLOCK_MONOTONIC, &end);

    // calculating time spent during the calculation and printing it
    time_spent = end.tv_sec - begin.tv_sec;
    time_spent += (end.tv_nsec - begin.tv_nsec) / 1000000000.0;
    printf("Elapsed time: %.2lf seconds.\n", time_spent);

    printf("\nNumber of solutions: %d\n", count);

    return 0;
}

如果我更改上部，并为数组动态分配内存，则会收到以下错误：

int NTHREADS, SIZE; 
int *hist;
hist = (int*)malloc(SIZE * sizeof(int));

然后我收到以下错误：

wikithread.c:8:1：警告：数据定义没有类型或存储类[默认启用] wikithread.c:8:1：错误：'hist' wikithread.c:7:6 的类型冲突：注意：以前'hist' 的声明在这里 wikithread.c:8:1: 错误: 初始化元素不是常量 wikithread.c: 在函数'solve'中: wikithread.c:23:27: 错误: 下标值既不是数组也不是指针也不是向量wikithread.c:23:27：错误：下标值既不是数组也不是指针也不是向量wikithread.c:26:7：错误：下标值既不是数组也不是指针也不是向量

任何人都可以帮我解决问题吗？

4

1 回答 1

2

您可以SIZE在未定义数组的情况下使用它来初始化数组——

int NTHREADS, SIZE; 
int hist[SIZE];

毫无疑问，这会导致问题。

至于你的第二个错误，你在文件范围内有这个：

hist = (int*)malloc(SIZE * sizeof(int));

但是在函数体之外不允许声明，只能声明。

于 2013-04-19T22:14:57.337 回答