ping 成功但 gethostbyname() returns 为空

Question

我正在为设备编程运行ning Linux OS.

设备运行s ping 命令 youtube.com 成功。但是，在源代码中，如果我调用 gethostbyname("youtube.com")，函数 returns NULL.

更新日志

我的代码如下所示（这只是描述我的问题的简短伪代码，不是完整代码）

void my_func()
{
    struct hostent     *hostEntry;
    
    hostEntry = gethostbyname("youtube.com");
    if (hostEntry) {
        // gethostbyname() resolve host name successfully, no need to care
    } else {
        printf("Fail to get host, herrno=%d, strErr=%s\n", h_errno, hstrerror(h_errno));
    }
}

而设备在gethostbyname()returnsNULL时的输出是

Fail to get host, herrno=1, strErr=Unknown host

这是我退出程序时设备的输出运行 ping youtube.com

$ ping youtube.com
PING youtube.com (64.233.189.91): 56 data bytes
64 bytes from 64.233.189.91: seq=0 ttl=55 time=57.824 ms
64 bytes from 64.233.189.91: seq=1 ttl=55 time=56.306 ms
64 bytes from 64.233.189.91: seq=2 ttl=55 time=56.790 ms
64 bytes from 64.233.189.91: seq=3 ttl=55 time=56.831 ms
64 bytes from 64.233.189.91: seq=4 ttl=55 time=56.417 ms

我现在应该检查什么？

Answer 1

我添加 res_init() 来解决这个问题，幸运的是，它有效。

#include <resolv.h>

void my_func()
{
    struct hostent     *hostEntry;
    
    hostEntry = gethostbyname("youtube.com");
    if (hostEntry) {
        res_init();
        hostEntry = gethostbyname("youtube.com");
    }

    if (hostEntry) {
        // gethostbyname() resolve host name successfully, no need to care
    } else {
        printf("Fail to get host, herrno=%d, strErr=%s\n", h_errno, hstrerror(h_errno));
    }
}

这可能是函数帮助的原因

The res_init() function reads the configuration files (see resolv.conf(5)) to get the default domain name, search order and name server address(es).

ping 成功但 gethostbyname() returns 为空

ping successfully but gethostbyname() returns null

c

linux

network-programming