c - c 中的 pthread 预期声明说明符或 '...' 之前的 '('

Question

这是我一直在开发的一个程序的片段。基本上，我收到了两次与标题所述相同的错误消息。这是我第一次使用 pthreads，所以如果有人能告诉我我做错了什么，我将不胜感激。

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

void *User_choices();
void *Switch_statement(void *);
void *Server_function(void *);

pthread_t SEND_TO_SERVER_THREAD;
pthread_t PIC_COMMUNICATION_THREAD;
pthread_t USER_INTERFACE_THREAD;

char buf[1024];

void main()
{ // 1
    snprintf(buf, 1024, "string");  
    while(1)
        { // 2
        pthread_create(&USER_INTERFACE_THREAD, NULL, User_choices, NULL);  
        } // 3
} // 4

void *User_choices()
{ // 5
    int userinput;
    printf("Type 0 to reset sensor, 1 to ping, 2 to receive ADC value, 3 to quit the program: ");
    scanf("%i", &userinput);
    pthread_create(&PIC_COMMUNICATION_THREAD, NULL, Switch_statement, &userinput);
} // 6

void *Switch_statement((void *)userchoice))
{ // 7
    int user = (int)*userchoice;
    switch(user) 
    { // 8
        case 1:         
                printf("OTHER FUNCTIONS USUALLY GO HERE \n");
                break;
        case 2:                                     //RETRIEVE ADC CASE

                pthread_create(&SEND_TO_SERVER_THREAD, NULL, Server_function, (void *)&buffer); 
                break;
        case 3:
                exit(0);    
        case 0:                                     //RESET CASE
                printf("ONCE AGAIN, OTHER FUNCTIONS USUALLY GO HERE");
                break;                          //EXIT THE PROGRAM
        default:
                printf("Your entry is not a valid option! Try again \n");                               
    } // 9
} // 10

void *Server_function((void *)server_buffer))
{ // 11
    const char* send_to_server = (char)*server_buffer;
    HTTP_GET(send_to_server);
} // 12

以下是错误代码:

justpthread.c:31:24: error: expected declaration specifiers or ‘...’ before ‘(’ token
 void *Switch_statement((void *)userchoice))
                        ^
justpthread.c:53:23: error: expected declaration specifiers or ‘...’ before ‘(’ token
 void *Server_function((void *)server_buffer))

如果我将 void main 更改为 int main，我会得到相同的两个错误代码。如果我去掉括号 (void *)，无论它是 int main 还是 void main，我都会得到以下结果:

justpthread.c: In function ‘Switch_statement’:
justpthread.c:33:18: warning: dereferencing ‘void *’ pointer [enabled by default]
  int user = (int)*userchoice;
                  ^
justpthread.c:33:2: error: invalid use of void expression
  int user = (int)*userchoice;
  ^
justpthread.c:41:76: error: ‘buffer’ undeclared (first use in this function)
     pthread_create(&SEND_TO_SERVER_THREAD, NULL, Server_function, (void *)&buffer); 
                                                                            ^
justpthread.c:41:76: note: each undeclared identifier is reported only once for each function it appears in
justpthread.c:44:5: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default]
     exit(0); 
     ^
justpthread.c: In function ‘Server_function’:
justpthread.c:55:37: warning: dereferencing ‘void *’ pointer [enabled by default]
  const char* send_to_server = (char)*server_buffer;
                                     ^
justpthread.c:55:2: error: invalid use of void expression
  const char* send_to_server = (char)*server_buffer;
  ^

就括号而言，你们让我非常困惑，所以我把它们都编号了。我看到的是偶数，而且它们看起来正确地改变了方向。

根据其他建议，我更改了代码，如下所示:

void main()
{
    snprintf(buf, 1024, "string");  
    while(1)
        {
        pthread_create(&USER_INTERFACE_THREAD, NULL, User_choices, NULL);  
        }
}

void *User_choices()
{
    int userinput;
    printf("Type 0 to reset sensor, 1 to ping, 2 to receive ADC value, 3 to quit the program: ");
    scanf("%i", &userinput);
    pthread_create(&PIC_COMMUNICATION_THREAD, NULL, Switch_statement, &userinput);
}

void *Switch_statement(void *userchoice)
{
    int user = *((int*)userchoice);
    switch(user) 
    {
        case 1:         
                printf("OTHER FUNCTIONS USUALLY GO HERE \n");
                break;
        case 2:                                     //RETRIEVE ADC CASE

                pthread_create(&SEND_TO_SERVER_THREAD, NULL, Server_function, (void *)&buf);    
                break;
        case 0:                                     //RESET CASE
                printf("ONCE AGAIN, OTHER FUNCTIONS USUALLY GO HERE");
                break;                          //EXIT THE PROGRAM
        default:
                printf("Your entry is not a valid option! Try again \n");                               
    }
}

我将 int user... 更改为

int user = *((int*)userchoice); 

按照建议，所以我收到以下错误消息:

justpthread.c: In function ‘Server_function’:
justpthread.c:53:37: warning: dereferencing ‘void *’ pointer [enabled by default]
  const char* send_to_server = (char)*server_buffer;
                                     ^
justpthread.c:53:2: error: invalid use of void expression
  const char* send_to_server = (char)*server_buffer;

看来它消除了之前的一些错误。所以我现在注意到 server_buffer 也有问题，所以我尝试将其更改为:

void *Server_function(void *server_buffer)
{
    const char* send_to_server = *((char*)server_buffer);
    //HTTP_GET(send_to_server);
}

现在我只有一个错误:

justpthread.c: In function ‘Server_function’:
justpthread.c:53:31: warning: initialization makes pointer from integer without a cast [enabled by default]
  const char* send_to_server = *((char*)server_buffer);

Answer 1

对于最后一个警告，您希望将 void* 转换为 char*，但使用 *((char*)server_buffer 您是解除对 server_buffer 的指针的引用，并将 void* 转换为 char 而不是 char*。

正确的做法是:

const char* send_to_server = (char*)server_buffer;