C++ - 函数返回，但不交回控制权

Question

我正在使用 C++ 为 Linux 开发另一个套接字库，作为个人练习。这是我的代码:

#ifndef SOCKET_H
#define SOCKET_H

#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <iostream>
using namespace std;

/**
 * Creates a struct to hold all the necessary information to create a socket.<br/>
 * Typically, you should not need to call this yourself, as it is done when you     call         listen() or dial()
 * @param host The hostname or IP address to connect to.
 * @param service The service on that machine (e.g "http" or "80")
 * @param sock The type of socket ("tcp" or "udp")
 * @return A addrinfo struct with all the required information to create a connection.
 */
addrinfo setup(const char *host,const char *service,const char *sock) {
    struct addrinfo hints;
    struct addrinfo *serv;
cout << "2.call to setup()\n";
//cout << "3.setup() returns here.\n";
//return *serv;
    int status=0;
/*struct addrinfo hints;
    struct addrinfo *serv;*/

    memset(&hints,0,sizeof hints);
    hints.ai_family=AF_UNSPEC;
    if (sock=="tcp") {
    hints.ai_socktype=SOCK_STREAM;
    } else if (sock=="udp") {
        hints.ai_socktype=SOCK_DGRAM;
    } else {
        fprintf(stderr,"[!] xsockets: error: unknown socket type %s\n",sock);
        exit(2);
    }
    hints.ai_flags=AI_PASSIVE;

    if ((status=getaddrinfo(host,service,&hints,&serv))!=0) {
        fprintf(stderr, "[!] xsockets: error: getaddrinfo error: %s\n",     gai_strerror(status));
        exit(1);
    }
    cout << "3.setup() returns here.\n";
    return *serv;
}

/**
 * Listens on a portand returns a scoket file descriptor.
 * @param service The service on this machine (e.g "http" or "80")
 * @param sock The type of socket ("tcp" or "udp")
 * @return A socket filde descriptor.
 */
int listen(const char *service,const char *sock) {
    cout << "1.call to listen()\n";
    struct addrinfo *serv;
    *serv=setup(NULL,service,sock);
    cout << "4.is this ever called?";
    int sockfd=socket(serv->ai_family,serv->ai_socktype,serv->ai_protocol);
    int status=bind(sockfd,serv->ai_addr,serv->ai_addrlen);
    if (status!=0) {
        fprintf(stderr,"[!] xsockets: error: bind error:                         %s\n",gai_strerror(status));
        exit(3);
}
    cout << "5.listen() returns here.";
    return sockfd;
}
#endif

如果我运行它，它会到达#3“setup() 返回这里”但永远不会到达#4“这是否被调用过？”更不用说 #5 “listen() 在这里返回”

谁能告诉我哪里出了问题。

我在 Ubuntu Linux 上，以 root 权限运行它。它是用 g++ 命令编译的。

这是我得到的:

Answer 1

你有未定义的行为，因为你没有初始化指针 serv 但随后立即用 *serv 取消引用它。

尽管如此，在调试时，您应该确保通过将 std::flush 或 std::endl 插入 std::来刷新输出输出:

cout << "4.is this ever called?" << std::endl;