Question

基本上，我在main中创建一个包含10个元素的数组，并创建两个线程。第一个线程calcOddIndex将计算数组中具有奇数索引的所有元素的乘积。第二个线程calcEvenIndex将计算数组中具有偶数索引的所有元素的乘积。 Main将在两个子线程完成后最终输出结果。

它给出了以下错误。我想我没有正确地将数组传递给pthread_create。我该如何解决这个问题？

g++ -c -Werror main.cc
main.cc:24:2: error: no matching function for call to 'pthread_create'
        pthread_create(&tidOdd, &attr, calcOddIndex, &array);
        ^~~~~~~~~~~~~~
/usr/include/pthread.h:326:5: note: candidate function not viable: no known
      conversion from 'void *(int *)' to 'void * _Nullable (* _Nonnull)(void *
      _Nullable)' for 3rd argument
int pthread_create(pthread_t _Nullable * _Nonnull __restrict,
    ^
main.cc:26:2: error: no matching function for call to 'pthread_create'
        pthread_create(&tidEven, &attr, calcEvenIndex, &array);
        ^~~~~~~~~~~~~~
/usr/include/pthread.h:326:5: note: candidate function not viable: no known
      conversion from 'void *(int *)' to 'void * _Nullable (* _Nonnull)(void *
      _Nullable)' for 3rd argument
int pthread_create(pthread_t _Nullable * _Nonnull __restrict,
    ^
2 errors generated.
make: *** [main.o] Error 1

这是我的代码：

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

/* first thread will calculate the product of all elements with odd index inside the array */
void *calcOddIndex(int arr[10]); 
int oddIndexProduct = 1; 
/* the second thread will calculate the product of all elements with even index inside the array */
void *calcEvenIndex(int arr[10]); 
int evenIndexProduct = 1; 

int main() {
    pthread_t tidOdd; /* the thread identifier for calcOddIndex */
    pthread_t tidEven; /* the thread identifier for calcEvenIndex */
    pthread_attr_t attr; /* set of thread attributes */

    /* create an array with at least 10 elements */
    int array[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

    /* get the default attributes */
    pthread_attr_init(&attr);

    /* create thread for calcOddIndex */
    pthread_create(&tidOdd, &attr, calcOddIndex, &array);
    /* create thread for calcEvenIndex */
    pthread_create(&tidEven, &attr, calcEvenIndex, &array);

    /* wait until both threads is done with their work */
    pthread_join(tidOdd, NULL);
    pthread_join(tidEven, NULL);

    // print the product of all elements with odd index
    printf("product of odd index inside the array = %d\n", oddIndexProduct);
    // print the product of all elements with even index
    printf("product of even index inside the array = %d\n", evenIndexProduct);

} // end of main

/*
calculate the product of all elements with odd index inside the array
*/ 
void *calcOddIndex(int arr[10]) {
    for (int i=1; i<10; i=i+2) {
        oddIndexProduct *= arr[i];
    }
    pthread_exit(0);
} // end of calcOddIndex

/*
calculate the product of all elements with even index inside the array
*/
void *calcEvenIndex(int arr[10]) {
    for (int i=0; i<10; i=i+2) {
        evenIndexProduct *= arr[i];
    }
    pthread_exit(0);
} // end of calcEvenIndex

Answer 1

你需要将你的arr作为（void *）传递：

proto：

void *calcOddIndex(void*);
void *calcEvenIndex(void*);

func：

void *calcOddIndex(void* ptr) {
int* arr = (int*) ptr;
for (int i=1; i<10; i=i+2) {
    oddIndexProduct *= arr[i];
}
pthread_exit(0);
}

和

void *calcEvenIndex(void* ptr) {
int* arr = (int*) ptr;
for (int i=0; i<10; i=i+2) {
    evenIndexProduct *= arr[i];
}
pthread_exit(0);
}

如何修复没有匹配函数来调用＆＃39; pthread_create＆＃39;在多线程？

1 个答案: