Question

所以，作为前言，我是C的新手，所以请原谅我的课程有任何可怕的错误。

我正在尝试编写一个程序，该程序将作为参数传递给程序或包含在传递路径的文件中。

它将数字存储到数组中，并存储数组的第一个元素中有多少个数字。它最多只能存储100个数字。

然后创建一个pthread并将指向数组的指针传递给线程。

然后假设线程总结数字并将总和返回主函数。

我遇到了以下问题：

1。它并不总是发生，但有时我会在代码行之前得到一个分段错误：

printf("Begining to create the thread");

2。我尝试归还这笔款项是行不通的，经过数小时的网上研究，我无法弄清楚原因。

3。编译程序时，出现以下错误：

gcc -g -o assn3 assn3.c -pthread
assn3.c: In function ‘AddUpNumbers’:
assn3.c:34:9: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
  return (void*)total;
         ^
assn3.c: In function ‘main’:
assn3.c:96:3: warning: passing argument 1 of ‘pthread_join’ makes integer from pointer without a cast [enabled by default]
   pthread_join(&functionThread, &total);
   ^
In file included from assn3.c:12:0:
/usr/include/pthread.h:261:12: note: expected ‘pthread_t’ but argument is of type ‘pthread_t *’
 extern int pthread_join (pthread_t __th, void **__thread_return);
            ^
assn3.c:97:3: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘void *’ [-Wformat=]
   printf("The total returned by the thread is %d", total);
   ^

这是我的代码：

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

#define NO_ARGS 1
#define ONLY_SINGLE_ARG 2
#define PATH_TO_READ_FROM 1
#define MAX_NUMBERS 101
#define MAX_CHAR_INPUT 255
#define COUNT_LOCATION 0

void* AddUpNumbers(void* arrayPointer) {
    printf("Created the pthread!");
    int* numbersArray = (int*)arrayPointer;
    int count = numbersArray[COUNT_LOCATION];
        int total = 0;

        int i = 1;
        while (i < count) {
                total = total + numbersArray[i];
        }
    printf("The total to be returned is %d", total);
    return (void*)total;
}

int main(int argc, char* argv[]) {
    FILE * numbersFile = NULL;
    int count = 0;
    int numberArray[MAX_NUMBERS];
    //Initialize the Array
    int i = 0;
    while (i < MAX_NUMBERS) {
        numberArray[i] = 0;
        i = i + 1;
    }

    if (argc == NO_ARGS) {
        printf("Usage: # or file path, #, #, ..., #\n");
    } else if (argc == ONLY_SINGLE_ARG) {
        numbersFile = fopen(argv[PATH_TO_READ_FROM], "r");
        if (numbersFile != NULL) {
            char buff[MAX_CHAR_INPUT];
            i = 1;
            count = 0;
            while (i < MAX_NUMBERS) {
                if (fscanf(numbersFile, "%s", buff) != EOF) {
                    numberArray[i] = atoi(buff);
                    printf("%d\n", numberArray[i]);
                                    i = i + 1;
                    count = count + 1;
                } else {
                    break;
                }
            }
            numberArray[COUNT_LOCATION] = count;
            printf("Count Total: %d\n", numberArray[COUNT_LOCATION]);
        } else {
                       printf("Error: Could not open file!\n");
                        return -1;
        }
    } else if (argc < MAX_NUMBERS + 1) {
        i = 1;
        count = 0;
        while (i < argc) {
            numberArray[i] = atoi(argv[i]);
            printf("%d\n", numberArray[i]);
            i = i + 1;
            count = count + 1;
        }
        printf("See if error happens after this");
        numberArray[COUNT_LOCATION] = count;
        printf("Count Total: %d\n", numberArray[COUNT_LOCATION]);
    } else {
                printf("Too many numbers! This program can only add up to: %d numbers.\n", MAX_NUMBERS);
                return -1;
    }
    printf("Begining to create the thread");
    pthread_t functionThread;
    int creationSuccess = 0;

    void* total;

    creationSuccess = pthread_create(&functionThread, NULL, AddUpNumbers, (void*)numberArray);
    if (creationSuccess == 0) {
        pthread_join(&functionThread, total);
        printf("The total returned by the thread is %d", *((int)total));
    } else {
        printf("Something went wrong.\n");
    }
    if (numbersFile != NULL) {
        fclose(numbersFile);
    }
    return 0;
}

我的Makefile看起来像这样：

assn3: assn3.c
    gcc -g -o assn3 assn3.c -pthread

Answer 1

您应该非常警惕编译器警告。要么清理它们，要么很清楚为什么它们没问题。请特别注意有关数据类型不匹配的警告。

在这种情况下，此警告可能解释了主要问题：

In file included from assn3.c:12:0:
/usr/include/pthread.h:261:12: note: expected ‘pthread_t’ but argument is of type ‘pthread_t *’
 extern int pthread_join (pthread_t __th, void **__thread_return);
        ^

您正在（创建并）传递指向pthread_t对象的指针作为pthread_join()的第一个参数，但与pthread_create()不同，pthread_join()期望您传递{ {1}}本身，而不是指向它的指针。随之而来的是各种各样的破坏（技术上，＆＃34;未定义的行为＆＃34;）。

UPDATE ：此外，您传递给pthread_t的第二个参数是指向pthread_join()的未初始化指针。如果void尝试写任何指向的地方，那么谁知道会发生什么（再次定义未定义的行为）。您应该将有效指针传递给要写入结果的位置。在这种情况下，那将是pthread_create()。

Answer 2

pthread_create的语法是：

int pthread_create(pthread_t *thread, const pthread_attr_t *attr,  *(*start_routine) (void *), void *arg);

pthread_t - 是线程的id。因此，如果您有很多线程，请创建变量pthread_t id或值数组，例如pthread_t id[THREAD_NUM]; 然后你的func会看起来像：
pthread_create(&id[i], NULL, &functionThread, (void*)numberArray);

With pthread_join(&functionThread, total);

同样的事情。

int pthread_join(pthread_t thread, void **value_ptr);

所以你加入必须看起来像：

 pthread_join(&id[i], total);

pthread程序

2 个答案: