Question

距离我开始寻找错误已经一个小时了。我刚开始使用C套接字。打印“错误1连接错误”后，程序以代码-1退出。在线服务器是一台netcat服务器。我在哪里搞砸了？

#include <stdio.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>

#define HOST "127.0.0.1"
#define PORT 4444

int main(int argc, const char *argv[])
{
    struct sockaddr_in addr;
    int sock = 0;
    int ret;
    struct sockaddr_in server_addr;
    char *msg = "Hello world !\n";
    char inBuffer[1024] = { 0 };
    if (sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP) < 0)
    {
        printf("Error %d socket creating.\n", sock);
        exit(-1);
    }
    else
    {
        memset(&server_addr, '0', sizeof(server_addr));

        server_addr.sin_family = AF_INET;
        server_addr.sin_port = htons(PORT);
        if (ret = inet_pton(AF_INET, HOST, &server_addr.sin_addr) <= 0)
        {
            printf("Error %d unsuported address: %d\n", ret);
            exit(-2);
        }
        else
        {
            if (ret = connect(sock, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0)
            {
                printf("Error %d connection error\n", ret);
                exit(-3);
            }
            else
            {
                send(sock, msg, strlen(msg), 0);
                read(sock, inBuffer, 1024);
                printf("%s\n", inBuffer);
                return 0;
            }
        }
    }



}

Answer 1

由于operator precedence，表达式

sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP) < 0

实际上等于

sock = (socket(AF_INET, SOCK_STREAM, IPPROTO_TCP) < 0)

也就是说，您将比较结果socket(AF_INET, SOCK_STREAM, IPPROTO_TCP) < 0分配给变量sock。该比较的结果将始终为0（对于false）或1（对于true）。 0和1都不应该是有效的套接字。

您需要为分配明确添加括号：

(sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0

connect调用和那里的比较需要做的相同。

C套接字编程错误

1 个答案: