如何每次都跟踪最大数量的文件描述符，而不是使用FD_SETSIZE(可能很大)？到目前为止，代码是(改编自“Beginning Linux Programming，2nd Edition”):
#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <sys/time.h>
#include <sys/ioctl.h>
#include <unistd.h>
#define SERVER_PORT 9734
#define ALLOWED_CLIENTS INADDR_ANY
#define BACKLOG 5
#define DELAY 0
int main()
{
int server_sockfd, client_sockfd;
socklen_t server_len, client_len;
struct sockaddr_in server_address, client_address;
int result;
fd_set readfds, testfds;
server_sockfd = socket(AF_INET, SOCK_STREAM, 0);
server_address.sin_family = AF_INET;
server_address.sin_addr.s_addr = htonl(ALLOWED_CLIENTS);
server_address.sin_port = htons(SERVER_PORT);
server_len = sizeof(server_address);
bind(server_sockfd, (struct sockaddr *)&server_address, server_len);
listen(server_sockfd, BACKLOG);
FD_ZERO(&readfds); /* Initialise readfds fd_set struct */
FD_SET(server_sockfd, &readfds); /* Initialise readfds to handle input from server_sockfd */
while(1) {
char ch;
int fd;
int nread;
testfds = readfds;
printf("Server waiting...\n");
/* Wait indefinitely for client request (input) using testfds */
result = select(FD_SETSIZE, &testfds, (fd_set *)0, (fd_set *)0, (struct timeval *)0);
if(result < 1) {
perror("Server 5");
exit(1);
}
/* At this stage, activity of a client trying to connect has been found.
* We will find which descriptor it is on by checking each in turn. */
for(fd = 0; fd < FD_SETSIZE; fd++)
{
if(FD_ISSET(fd, &testfds)) { /* If activity occurs on the given file descriptor... */
if(fd == server_sockfd) { /* If activity occurs on server_sockfd, it must be
* a request for a new connection */
client_len = sizeof(client_address);
/* Extract connection request - set client_sockfd equal to this */
client_sockfd = accept(server_sockfd, (struct sockaddr *)&client_address, &client_len);
/* Add client_sockfd to the descriptor set */
FD_SET(client_sockfd, &readfds);
printf(" -Added client (fd %d)\n", fd);
}
else
{
ioctl(fd, FIONREAD, &nread); /* Find out how much data needs to be read in */
if(nread == 0) { /* No data left - finished with this client */
close(fd);
FD_CLR(fd, &readfds);
printf(" -Removed client (fd %d)\n", fd);
}
else {
read(fd, &ch, 1); /* Carry out the server's actual function */
sleep(DELAY);
printf(" -Serving client (fd %d)\n", fd);
ch++;
write(fd, &ch, 1);
}
}
}
}
}
}
这本书接着说，这将使其效率大大降低，这是有道理的，并且应该使用变量来跟踪最大的fd数连接，但是我只是不知道如何实现这一点，花了很多时间进行实验。提前致谢。
最佳答案
您应该有一个变量，例如int maxfd，每当您的代码包含FD_SET()或FD_CLR()时，您就可以对其进行调整。 this question的答案包含正确调整maxfd的示例。
与注释不同，我认为您不需要将“the”(哪个the？)变量static设置为。这些评论对民意测验和epoll是正确的，但是知道如何使用select也是有用的。
关于c - Posix套接字: Find out greatest number of file descriptors，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/17137811/