gethostbyport() -- 根据端口号获取服务信息

beyes

和getservbyname() 函数类似，gethostbyport() 函数可以根据给定的端口号来获取相关的服务信息，函数声明如下：

[Plain Text] 纯文本查看 复制代码

#include <netdb.h>
struct servent *getservbyport(int port, const char *proto);

第 1 个参数是端口号。
第 2 个参数指定用的是哪种协议。

测试代码：

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#include <stdio.h>
#include <stdlib.h>
#include <netdb.h>

int main(int argc, char **argv)
{
    struct servent *myserv;
    int port;

    if (argc < 3) {
              puts("Incorrect parameters. Use:");
             printf("%s service-port protocol-name", argv[0]);
              return EXIT_FAILURE;
    }


    port = htons(atoi(argv[1]));

    if (strcmp(argv[2], "NULL") == 0) {
        myserv = getservbyport(port, NULL);
        if (myserv == NULL) {
            printf("Port \"%s\" not found for protocol \"%s\"\n", argv[1], argv[2]);
            exit(EXIT_FAILURE);
        }
        printf ("Name: %-15s  Port: %5d    Protocol: %-6s\n", myserv->s_name, ntohs(myserv->s_port), myserv->s_proto);
    }
        
    else {
        myserv = getservbyport(port, argv[2]);
        if (myserv == NULL) {
            printf("Port \"%s\" not found for protocol \"%s\"\n", argv[1], argv[2]);
            exit(EXIT_FAILURE);
        }
        printf ("Name: %-15s  Port: %5d    Protocol: %-6s\n", myserv->s_name, ntohs(myserv->s_port), myserv->s_proto);
    }

    return 0;
}

运行输出：

# ./getservbyport 21 udp
Name: fsp              Port:    21    Protocol: udp  
# ./getservbyport 21 tcp
Name: ftp              Port:    21    Protocol: tcp  
# ./getservbyport 21 NULL
Name: ftp              Port:    21    Protocol: tcp  
# ./getservbyport 32 tcp
Port "32" not found for protocol "tcp"

函数如果找不到相应的“端口--服务” 匹配项时，返回 NULL 空指针。