how to check for null/empty string value of LPCTSTR

Question

_{Thursday, March 29, 2007 5:43 AM}

hello

i have these sample codes which has some problems:

(LPCTSTR sAppName, LPCTSTR sServer, int nPort, CString sFile)

if ((sAppName == L"") || (sServer == L"") || (nPort == 0) || (sFile == L""))
    {
        return 0;
    }

When I pass an empty string for sFile, it will return 0;
But when I pass an empty string for sAppName and sServer, it will not return 0 but instead it will continue with the rest of the codes below.

How to check for null or empty string value for LPCTSTR?

thanks

All replies (9)

_{Thursday, March 29, 2007 6:46 AM ✅Answered}

if ((sAppName == _T('\0')) || (sServer == _T('\0')) ||         (nPort == 0) || (sFile == L""))     {         return 0;     }

Modify your code to,

if ((wcslen(sAppName) == 0 ) || (

wcslen(sServer) == 0 ) ||
        (nPort == 0) || (sFile.IsEmpty() == TRUE))
    {
        return 0;
    }

Make sure sAppName, and  sServer

 are pointing to empty string.

_{Thursday, March 29, 2007 5:56 AM}

I hope this works:

Code Snippet

if( sAppName == NULL || *sAppName == _T('\0') || . . .

_{Thursday, March 29, 2007 6:09 AM}

thank you very much

i modified the codes into this:

if ((sAppName == _T('\0')) || (sServer == _T('\0')) ||
        (nPort == 0) || (sFile == L""))
    {
        return 0;
    }

but still it will not get inside the return 0 statement when I pass an empty string.

i gave values this way:

dwStatusActual = pNS->GetWebFile(L"", sFixedServerName, nFixedPort,
                sFixedFileName);

wherein the first parameter is an empty string.
so it should return 0 when the if statement is processed.

thanks

_{Thursday, March 29, 2007 6:38 AM}

I think you should further modify it into this:

Code Snippet

if( *sAppName == _T('\0') || *sServer == _T('\0') || nPort == 0 || sFile.IsEmpty())

{

    return 0;

}

I hope it works now.

_{Thursday, March 29, 2007 6:41 AM}

What you do is not correct. You compare a const pointer to char* with a character. That is not going to work. You should follow Viorel's indications. If you want to compare a LPCTSTR with a string literal, you should use strcmp(), or macro _tcscmp().

Code Snippet

if(_tcscmp(sAppName, _T("something")) == 0)
  ...

_{Thursday, March 29, 2007 7:04 AM}

i changed my codes to this:

if ((*sAppName == _T('\0')) || (*sServer == _T('\0')) ||
        (nPort == 0) || (sFile == L""))
    {
        return 0;
    }

and it worked fine....

i also used this kind of code by **Prasad Somwanshi
**and it also worked.

if ((wcslen(sAppName) == 0 ) || (wcslen(sServer) == 0 ) ||
        (nPort == 0) || (sFile.IsEmpty() == TRUE))
    {
        return 0;
    }

thanks to all.

_{Thursday, March 29, 2007 7:14 AM}

Hi,

Can the following code be considered as valid answer for the above question?

Thanx,

Ch.T.Gopi Kumar.

_{Thursday, March 29, 2007 3:52 PM}

If whitespaces are considered to contribute to "emptyness" then that implementation of IsEmptyString() is correct. But I wouldn't introduce the MFC dependency if there wasn't already one there.

I would have answered the original post by suggesting two inlined versions to be placed in a shared header:

Code Snippet

inline bool IsNullOrEmpty( const char* str )
{
   return (str == 0) || (*str == '\0');
}

inline bool IsNullOrEmpty( const wchar_t* str )
{
   return (str == 0) || (*str == L'\0');
}

 
For whitespace trimming, I would provide separate functions.  This is best done by providing a function that returns std :: string.  Use string :: empty().  Note that the string( const char* ) constructor must take a non-null value.

e.g.
assert( szText != 0 );  // we should always have a string
string trimmedStr = TrimString( szText );

e.g.
if( (szText != 0) || TrimString(szText).empty() ) ...

In general, its better practice to always have non-null strings, and limit your use of IsNullOrEmpty().  Keep your local state constrained to values that you can easily deal with, rather than propating the null-case all over your code. 

And finally, start getting in the habit of using std :: string more than C-strings, less you really have a performance requirement (and there usually isn't one when it comes to strings). 

Brian

_{Thursday, March 29, 2007 4:03 PM}

Thanks Brain for good explanation and the suggestions.

Best Regards,

Ch.T.Gopi Kumar.