DnsFlushResolverCache 清除windows DNS缓存

效果等同于ipconfig /flushdns 命令。
DnsFlushResolverCache 函数是在Dnsapi.dll导出，该函数没有任何参数。MSDN中找不到他，看来是个Undocumented函数，函数原型：

BOOL WINAPI DnsFlushResolverCache(VOID);

BOOL __stdcall DnsFlushResolverCache()
{
    BOOL bRet = FALSE;  

    typedef BOOL (WINAPI *PfuncDnsFlushResolverCache)(VOID);
    HMODULE hDnsModule = LoadLibrary( _T("dnsapi.dll") );
    if ( hDnsModule != NULL )
    {
        PfuncDnsFlushResolverCache pFlushFun = GetProcAddress( hDnsModule, "DnsFlushResolverCache" );
        if ( pFlushFun != NULL )
        {
            pFlushFun();
            bRet = TRUE;
        }  

        FreeLibrary( hDnsModule );
    }  

    return bRet;
}

vb6 申明:

Private Declare Function DnsFlushResolverCache Lib "dnsapi.dll" () As Long