[英]C function argument to set values for global variables?
我正在创建可以向函数传递的参数变量声明值的函数。
例如,从我的server.c文件中:
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) {
}
}
从我的serverAPI.h文件中:
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);
}
这就是我所拥有的...
而且我期望从'setServer'函数中,传递的变量(即ServerAddress和sfd)的值将由该函数声明,但是还没有...
因此,setServer函数内部的返回值为:
serverAddress.sin_port = 12345
sfd = 3
listenv = 0
从主要方面:
serverAddress.sin_port = 0
sfd = 0
listenv = 0
因为它已被列为全球。
我必须将什么设置为setServer的参数,以便它可以设置全局变量的值?
当C通过copy-by-value传递参数时,在修改sfd
或saddr
,您只能自行修改参数,即传递的参数的副本。 您需要传递指针以实际修改变量。 像这样声明setServer
:
int setServer (char * portn, struct sockaddr_in* saddr, int* sfd);
添加解引用运算符:
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);
并使用指针调用setServer
:
listenv = setServer(argv[1],&serverAddress,&sfd);
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