c - Printf 在套接字调用之前不工作

Question

当使用参数“server”调用程序时，“runserver”方法被执行并且一切正常。只是 printf() 语句不打印任何内容。但是当我调用“runclient”方法时，之前的 printf 工作正常。为什么会这样？如何解决这个问题？

#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <strings.h>
#include <sys/types.h>
#include <netdb.h>

void error(char *msg)
{
    perror(msg);
    exit(1);
}

int runclient()
{
    int sockfd, portno, n;

    struct sockaddr_in serv_addr;
    struct hostent *server;

    char buffer[256];

    portno = 1024;
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0)
        error("ERROR opening socket");
    server = gethostbyname("localhost");
    if (server == NULL) {
        fprintf(stderr,"ERROR, no such host\n");
        exit(0);
    }
    bzero((char *) &serv_addr, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    bcopy((char *)server->h_addr,
          (char *)&serv_addr.sin_addr.s_addr,
          server->h_length);
    serv_addr.sin_port = htons(portno);
    if (connect(sockfd,(struct sockaddr *)&serv_addr,sizeof(serv_addr)) < 0)
        error("ERROR connecting");
    printf("Please enter the message: ");
    bzero(buffer,256);
    fgets(buffer,255,stdin);
    n = write(sockfd,buffer,strlen(buffer));
    if (n < 0)
        error("ERROR writing to socket");
    bzero(buffer,256);
    n = read(sockfd,buffer,255);
    if (n < 0)
        error("ERROR reading from socket");
    printf("%s\n",buffer);
    return 0;
}

int runserver(){
    int sockfd, portno, clilen;
    char buffer[256];
    struct sockaddr_in serv_addr, cli_addr;
    int n;
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0)
        error("ERROR opening socket");
    //bzero((char *) &serv_addr, sizeof(serv_addr));
    portno = 1024;
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = INADDR_ANY;
    serv_addr.sin_port = htons(portno);
    if (bind(sockfd, (struct sockaddr *) &serv_addr,
             sizeof(serv_addr)) < 0)
        error("ERROR on binding");
    listen(sockfd,5);
    clilen = sizeof(cli_addr);
    sockfd = accept(sockfd, (struct sockaddr *) &cli_addr, &clilen);
    if (sockfd < 0)
        error("ERROR on accept");
    //bzero(buffer,256);
    n = read(sockfd,buffer,255);
    if (n < 0) error("ERROR reading from socket");
    printf("Here is the message: %s\n",buffer);
    n = write(sockfd,"I got your message",18);
    if (n < 0) error("ERROR writing to socket");
    return 0;
}


int main(int argc, char **argv)
{
    if(strcmp(argv[1],"server") == 0){
        printf("Starting Server .... ");
        runserver();

    } else {
        printf("Starting Client .... ");
        runclient();
    }

    return 0;
}

Answer 1

stdout 在写入终端时是行缓冲的，因此您必须在适当的位置调用 fflush(stdout) 或添加换行符。