Cc 套接字编程 select() 的第一个参数

我一直在尝试用Linux进行一些网络编程，但我似乎又被卡住了。我似乎没有得到 select() 函数的第一个参数。 据我所知，它应该是最后一个制作的插座filedescriptor + 1。 大多数情况下，最高的filedescriptor包含数字 6。当我将filedescriptor添加到fd_set时，它突然变为 64——可能是因为它更改为fd_bytes(如果我错了，请纠正我)。因此，6+1 似乎不适合选择语句，因为它一直在阻塞，但如果我从fd_set获得fd_bytes则不会。我对所有这些感到非常困惑，并希望就该主题提供一些建议，或者如果有人有的话，可以为sigio提供很好的教程，可以使事情变得更容易。

服务器.cpp

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h> 
#include <sys/socket.h>
#include <netinet/in.h>
#include <boost/thread/thread.hpp>
#include <sys/time.h>
#include <sys/ioctl.h>
using namespace std;
void error(char *msg,int socket)
{
perror(msg);
close(socket);
exit(1);
}
int main(int argc, char** argv) {
int sockfd, newsockfd, portno, n;
socklen_t clilen;
fd_set readfds;
FD_ZERO(&readfds);
/*
* Sockfd, newsockfd contain values returned by the socket
* portno stores the port number on which the server accepts connections
* clilen stores the size of the address of the client
* n contains the amount of character written of read
*/
char buffer[256];
/* buffer contains the characters read from the socket*/
struct sockaddr_in serv_addr, cli_addr;
/* 
* sockaddr_in contains an internet address
* serv_addr contains the servers address
* cli addr contains the clients address
*/
if(argc < 2)
{
fprintf(stderr,"ERROR no port provided");
exit(1);
}
/*
* error if no argument
*/
sockfd = socket(AF_INET,SOCK_STREAM,0);
int opt = 1;
ioctl(sockfd, FIONBIO, &opt);
if(sockfd < 0){
error("ERROR opening socket", sockfd);
}    
/*
* socket() creates a new socket
* argument 1 contains the address domain
* argument 2 contains the socket type
* argument 3 contains the protocol should be 0
* socket() returns a reference for itself
*/
bzero((char*) &serv_addr, sizeof(serv_addr));
/* empty the serv_addr variable*/
portno = atoi(argv[1]);
/*converts the port argument from string  to int*/
serv_addr.sin_family = AF_INET;
/*set the code for the address family*/
serv_addr.sin_port = htons(portno);
/*htons converts the portno to network bytes and gives it to the server address*/
serv_addr.sin_addr.s_addr = INADDR_ANY;
/*set the server ip to the ip of the running machine*/
if(bind(sockfd,(struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0)
error("ERROR on binding", sockfd);
/*
* bind() binds a socket to an address, in this case the
* addess of the current host
*/
listen(sockfd,5);
/*the listen system call allows the process to listen on the socket for 
connections*/
clilen = sizeof(cli_addr);
do{
newsockfd = accept(sockfd,(struct sockaddr *) &cli_addr, &clilen);
}while(newsockfd < 0);
/*
* accept() lets the system wait until a client connects to the server
*/
FD_SET(newsockfd,&readfds);
int sockcount = pselect(readfds.fds_bits[0] + 1,&readfds,NULL,NULL,NULL,NULL);
bzero(buffer,256);
n = read(newsockfd,buffer,255);
if(n < 0) error("ERROR reading from socket", sockfd);
printf("Here is the message: %s", buffer);
/*
* bzero empties the buffer
* read obviously reads data from the new socket descriptor
*/
n = write(newsockfd,"I got your message",18);
if(n < 0) error("ERROR writing to socket", sockfd);
close(sockfd);
return 0;
}

一些(或全部)代码可能没有意义，但这主要是因为我只是在测试代码的行为方式，然后让它多线程。上面的代码工作得更少：可以使用 telnet 或位于此处 http://www.linuxhowtos.org/C_C++/socket.htm 教程中的客户端进行测试。