在 C 中将字符串分配给 Hostent

Question

我正在编写一些代码来查找 Web 服务器。它在 C 中。

我有这个

sprintf(pre_ip, "%d.%d.%d.%d", num1, num2, num3, num4);

num1-4 是一个类似 1.1.1.1 的 ip。这部分有效..

he = gethostbyname(pre_ip);

这应该将struct hostent *he; 分配给ip..

但这不起作用..

server_info.sin_addr = *((struct in_addr *)he->h_addr);
connect(socket_fd, (struct sockaddr *)&server_info, sizeof(struct sockaddr));

这是整个代码：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
//lol220
int main(int argc, char *argv[])
{
    struct sockaddr_in server_info;
    struct hostent *he;
    int socket_fd,num;
    char buffer[1024];

    char buff[1024];

    if (argc != 1) {
        fprintf(stderr, "Usage: client hostname\n");
        exit(1);
    }

    if ((socket_fd = socket(AF_INET, SOCK_STREAM, 0))== -1) {
        fprintf(stderr, "Socket Failure!!\n");
        exit(1);
    }

    memset(&server_info, 0, sizeof(server_info));
    server_info.sin_family = AF_INET;
    server_info.sin_port = htons(80);

//-------------------------------looooop------------------------
int num1 = 1;
int num2 = 1;
int num3 = 1;
int num4 = 1;
int done = 1;
char ip;
char pre_ip[256];
while(done){
        if(num4 == 256){
        num4 = 1;
        num3++;
        }
        if(num3 == 256){
        num3 = 1;
        num2++;
        }
        if(num2 == 256){
        num2 = 1;
        num1++;
        }
        if(num1 == 255 && num2 == 255 && num3 == 255 && num4 == 255){
        done = 0;
        }
        // MOST LIKELY NON WORKING PART 
        sprintf(pre_ip, "%d.%d.%d.%d", num1, num2, num3, num4);
        printf("%s\n", pre_ip);
        he = gethostbyname(pre_ip);
        server_info.sin_addr = *((struct in_addr *)he->h_addr);
            if (connect(socket_fd, (struct sockaddr *)&server_info, sizeof(struct sockaddr))<0) {
                printf("Could not connect to %s", he);
            }
            else{
                printf("Could connect to %s", he);
            }
        // MOST LIKELY NON WORKING PART 

num4++;
}
return 0;
}

它编译得很好。

打印“1.1.1.1”，然后显示“无法连接到 8T1.1.1.2”，这意味着 he == "8T1.1.1.2。

Answer 1

当你在这一行打印ip时：

printf("Could not connect to %s", he);

您将 struct hostent 转换为 char *，这会导致 ip 之前的奇数字符。其实用ip直接连接服务器就可以了，不用gethostbyname。如果你真的想试试这个功能，就这样吧：

bzero(&server_info, sizeof(server_info));
const char *ip = inet_ntoa(server_info.sin_addr);
...
printf("Could not connect to %s", ip);

Answer 2

试试类似的方法：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

int main(int argc, char *argv[])
{
    struct sockaddr_in server_info;
    int socket_fd;

    if (argc != 1) {
        fprintf(stderr, "Usage: client hostname\n");
        exit(1);
    }

    if ((socket_fd = socket(AF_INET, SOCK_STREAM, 0))== -1) {
        fprintf(stderr, "Socket Failure!!\n");
        exit(1);
    } 

    memset(&server_info, 0, sizeof(server_info));
    server_info.sin_family = AF_INET;
    server_info.sin_port = htons(80);

    for (uint32_t ip = 0x01010101; ip != 0xFFFFFFFF; ++ip) {
        server_info.sin_addr.s_addr = htonl(ip);
        printf("Connect to %s: ", inet_ntoa(server_info.sin_addr));
        if (connect(socket_fd, (struct sockaddr *)&server_info, sizeof(server_info)) == -1) {
            printf("Failed\n");
        }
        else {
            printf("Success\n");
            close(socket_fd);
            if ((socket_fd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
                fprintf(stderr, "Socket Failure!!\n");
                exit(1);
            } 
        }
    }
    return 0;
}