Get Host By Name (with a variable)

Question

2.50/5 (2 votes)

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I'm trying to get an IP address from an URL. This works fine when I use "www.dog.com" but when I want to use a variable it doesn't work.

C++

HOSTENT *pHostEnt;
int  **ppaddr;
SOCKADDR_IN sockAddr;
char* addr;
		
std::wstring site;
site = wsURL.c_str();
pHostEnt = gethostbyname("site");
ppaddr = (int**)pHostEnt->h_addr_list;
sockAddr.sin_addr.s_addr = **ppaddr;
addr = inet_ntoa(sockAddr.sin_addr);

Posted 8-Nov-11 12:43pm

Member 7766180

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Comments

Sergey Alexandrovich Kryukov 8-Nov-11 19:13pm

Always explain what does it mean "it does not work". Software developers don't say such words, they provide comprehensive issue report. Just forget using "it does not work".
--SA

Member 7766180 8-Nov-11 21:16pm

Your right. I tried this and received this error.

The code.....
BSTR bstr;
pBrowser->get_LocationURL(&bstr);
std::wstring wsURL;
wsURL = bstr;

size_t DSlashLoc = wsURL.find(L"://");
if (DSlashLoc != wsURL.npos)
{
wsURL.erase(wsURL.begin(), wsURL.begin() + DSlashLoc + 3);
}
DSlashLoc = wsURL.find(L"www.");
if (DSlashLoc == 0)
{
wsURL.erase(wsURL.begin(), wsURL.begin() + 4);
}
DSlashLoc = wsURL.find(L"/");
if (DSlashLoc != wsURL.npos)
{
wsURL.erase(DSlashLoc);
}
wprintf(L"\n Current Website URL: %s\n\n", wsURL.c_str());

HOSTENT *pHostEnt;
int **ppaddr;
SOCKADDR_IN sockAddr;
char* addr;
pHostEnt = gethostbyname(wsURL.c_str());
ppaddr = (int**)pHostEnt->h_addr_list;
sockAddr.sin_addr.s_addr = **ppaddr;
addr = inet_ntoa(sockAddr.sin_addr);
printf("\n Current Website IP:%s", addr);

1 IntelliSense: argument of type "const wchar_t *" is incompatible with parameter of type "const char *"

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Chuck O'Toole · Accepted Answer · 2011-11-08T13:26:00

Solution 1

How in the world is the API to know that "site" is the name of your variable and not the name of the host you are looking up?

pHostEnt = gethostbyname("site");

Do you see the quotation marks? What do you think that means?

No, I'm not going to give you the code that works, you'll not learn anything other than how to paste and you've demonstrated that you do that well.

Posted 8-Nov-11 13:26pm

Chuck O'Toole

Comments

Member 7766180 8-Nov-11 21:01pm

Yes I see the quotation marks. You right, they don't belong there.
I tried this...
std::wstring site;
site = wsURL.c_str();
pHostEnt = gethostbyname(site);
and get this error.
1 IntelliSense: no suitable conversion function from "std::wstring" to "const char *" exists

Chuck O'Toole 8-Nov-11 22:42pm

And after all your discussion with Richard in your other question (http://www.codeproject.com/Questions/280351/myfile-log-printing-weird) you should see that the error is telling you that you are using a "wide string" when the function takes a "char *" string. You've already done the conversion from string to wstring in that question, now do the reverse.

This is the problem with just cut / paste other people code and suggestions without understanding what is going on. You've now mixed wide and regular strings in your code and are having to deal with the consequences.

Member 7766180 8-Nov-11 23:24pm

Like this?

int Newlength = WideCharToMultiByte (CP_ACP, WC_COMPOSITECHECK, wsURL.c_str(), -1, NULL, 0, NULL, NULL);
std::string NewLogURL(Newlength+1, 0);
int Newresult = WideCharToMultiByte (CP_ACP, WC_COMPOSITECHECK, wsURL.c_str(), -1, &NewLogURL[0],Newlength+1, NULL, NULL);

HOSTENT *pHostEnt;
int **ppaddr;
SOCKADDR_IN sockAddr;
char* addr;

pHostEnt = gethostbyname(NewLogURL.c_str());

I'm trying Chuck. I really am! I think that I've learned alot, just a start.

Chuck O'Toole 8-Nov-11 23:26pm

Are you asking if I think it will work? Wouldn't trying it be the better way of finding out?

Member 7766180 8-Nov-11 23:39pm

Yes it works. Affirmation would be nice!

Chuck O'Toole 8-Nov-11 23:41pm

What better affirmation is there than watching your own code compile and execute properly? My "eyeballing" the code won't help a bit.

Member 7766180 8-Nov-11 23:45pm

OK, OK point taken! Thank you.