C函數參數爲全局變量設置值？

Question

我正在創建函數，可以將函數聲明值傳遞給參數變量。

例如，從我server.c文件：

int sfd; //socket file descriptor 
int listenv; //if listen 
struct sockaddr_in serverAddress; //server address 

int main(int argc, char * argv[]) { //argv[0] == server //argv[1] == port number 

    listenv = setServer(argv[1],serverAddress,sfd); 
      //int port = ntohs(serverAddress.sin_port); 
      printf("sfd = %d port = %d\n", sfd, ntohs(serverAddress.sin_port)); 
    while (listenv == 0) { 
    } 
} 

從我serverAPI.h文件：

int setServer (char * portn,struct sockaddr_in saddr,int sfd) { 

    saddr.sin_family = AF_INET; 
    saddr.sin_addr.s_addr = htonl(INADDR_ANY); 
    saddr.sin_port = (int)htons(atoi(portn)); 


    sfd = socket(AF_INET, SOCK_STREAM, 0); 
    if (sfd < 0) 
     error("ERROR opening socket"); 
    printf("Successfully opened socket sfd = %d\n",sfd); 

    if (bind(sfd, (struct sockaddr *) &saddr, sizeof(saddr)) == -1) 
     error("ERROR on binding"); 
    printf("Successfully Binded on port %d\n", ntohs(saddr.sin_port));//show correct port number 

    int listenv; 
    if((listenv = listen(sfd,5)) < 0) 
     error("ERROR on listening"); 
    //print message to show connection has been made 
    printf("Ready and Listening..."); 

    return (listenv); 
} 

這是我...

我期望從'setServer'函數中，通過變量（即ServerAddress和sfd），值將被該函數聲明，但它沒有...

所以setServer函數中的返回值是：

serverAddress.sin_port = 12345 
sfd = 3 
listenv = 0 

，並從主：

serverAddress.sin_port = 0 
sfd = 0 
listenv = 0 

，因爲它已被列爲全球。

我需要爲setServer設置什麼參數才能設置全局變量的值？

Answer 1

作爲C語言修改sfd或saddr當經過拷貝按值，參數，只修改參數itsself，即，傳遞的參數的副本。你需要傳遞指針來實際修改變量。聲明setServer這樣的：

int setServer (char * portn, struct sockaddr_in* saddr, int* sfd); 

添加非關聯化運營：

saddr->sin_family = AF_INET; 
saddr->sin_addr.s_addr = htonl(INADDR_ANY); 
saddr->sin_port = (int)htons(atoi(portn)); 


*sfd = socket(AF_INET, SOCK_STREAM, 0); 
if (*sfd < 0) 
    error("ERROR opening socket"); 
printf("Successfully opened socket sfd = %d\n",*sfd); 

if (bind(*sfd, (struct sockaddr *) saddr, sizeof(*saddr)) == -1) 
    error("ERROR on binding"); 
printf("Successfully Binded on port %d\n", ntohs(saddr->sin_port));//show correct port number 

int listenv; 
if((listenv = listen(*sfd,5)) < 0) 
    error("ERROR on listening"); 
//print message to show connection has been made 
printf("Ready and Listening..."); 

return (listenv); 

並調用setServer與指針：

listenv = setServer(argv[1],&serverAddress,&sfd);