C / C++ / MFC

11-Oct-05 22:06

I wonder how to convert a string from CString(MFC) to LPTSTR. I want to use my string in CString as a LPTSTR but i don't know to convert it.Please help me!
Thanks a lot

Rage11-Oct-05 22:18

Rage

11-Oct-05 22:18

In case you can do with a LPCTSTR (which in most cases is safer), you can easily convert a CString to a LPCTSTR, the CString class provides an operator CString::operator LPCTSTR to achieve that.

CString MyCString;
LPCTSTR mystring=MyCString.operator LPCTSTR();

To force the conversion to a non constant string, use the GetBuffer and ReleaseBuffer functions.

~RaGE();

cauvang12-Oct-05 1:15

12-Oct-05 1:15

Thanks for your helping me. But I don't want to return a LPTSTR, not a LPCTSTR.Anyway, thanks you a lot.

toxcct11-Oct-05 22:25

toxcct

11-Oct-05 22:25

CString already provides such an operator...

CString str = "Hello you";
char* pszTxt = (LPTSTR)str;

TOXCCT >>> GEII power
[toxcct][VisualCalc]

cauvang12-Oct-05 0:43

12-Oct-05 0:43

Thanks for your answering, but when I try doing the following code
LPTSTR CMainDlg::XuLyChuoi()
{
char *tmp_sz = new char[1000];
::GetWindowText(GetDlgItem(IDC_EDIT1),tmp_sz,1000);
CString s = tmp_sz;
int index = 1;
while ((index=s.Find("x", index)) != -1)
{
CString s1 = s[index-1];
s1+= s[index];
CString s2 = s[index-1];
s2+= "*";
s2+= s[index];
s.Replace(s1, s2);
}
tmp_sz = (LPTSTR)s;

return tmp_sz;
}

I have the error:

error C2440: 'type cast' : cannot convert from 'class WTL::CString' to 'char *'
No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
Error executing cl.exe.

- 1 error(s), 0 warning(s)

Can you explain?Thank you.

toxcct12-Oct-05 0:54

toxcct

12-Oct-05 0:54

put aroud your literal string some _T() because you seem to use UNICODE...

and also declare tmp_sz as a TCHAR*, not a char*

TOXCCT >>> GEII power
[toxcct][VisualCalc]

cauvang12-Oct-05 1:07

12-Oct-05 1:07

thanks again, but it still give me that error.

toxcct12-Oct-05 1:45

toxcct

12-Oct-05 1:45

LPTSTR CMainDlg::XuLyChuoi() {
    TCHAR* tmp_sz = <font color=blue>new</font> TCHAR[1000];
    ::GetWindowText(GetDlgItem(IDC_EDIT1), tmp_sz, 1000*<font color=blue>sizeof</font>(TCHAR));
    CString s = tmp_sz;
    <font color=blue>int</font> index = 1;
    <font color=blue>while</font> ((index = s.Find(_T(<font color=gray>"x"</font>), index)) != -1) {
        CString s1 = s[index-1];
        s1 += s[index];
        CString s2 = s[index-1];
        s2 += _T(<font color=gray>"*"</font>);
        s2 += s[index];
        s.Replace(s1, s2);
    }
    ::_tcscpy(tmp_sz, (LPTSTR)s); <font color=green>// Notice that you cannot affect a C-style string with the operator = !!!!</font>

    <font color=blue>return</font> tmp_sz;
}

TOXCCT >>> GEII power
[toxcct][VisualCalc]

icabod12-Oct-05 1:12

icabod

12-Oct-05 1:12

Not relating to the use of strings or conversion etc, but it looks to me like you have a chance of memory leakage here.
You allocate memory for the string on the heap, then copy this into a CString. Later on you change the pointer to point to the LPTSTR of the CString (I think it should maybe be LPCTSTR, as casting a CString will probably only be safe if cast to a const - which may explain the error you're getting).
This means that you lose the memory you allocated at the start of the function, as nothing's pointing to it any more. Also, you're returning a pointer to something which is about to be deleted (the CString will be deleted when you exit the function).
I think what you actually should be doing (tho' feel free to correct me) is to copy the contents of the CString into the address pointed to by tmp_sz, and then return the tmp_sz pointer. Just remember that you need to later on delete the pointer that you're returning.

So your last bit of code would do something like:

strcpy(tmp_sz, (LPCTSTR)s, s.GetLength());
return tmp_sz;

After making sure that the length of CString s is not > 1000 (including the NULL terminator).

Does that make sense? I'm speed-typing coz it's lunchtime and I'm hungry.

Tim Smith12-Oct-05 4:03

Tim Smith

12-Oct-05 4:03

Doing the following would work.

strncpy (tmp_sz, s, 1000);
tmp_sz [999] = 0; // strncpy doesn't place a null on a full buffer
return tmp_sz;

Tim Smith

I'm going to patent thought. I have yet to see any prior art.

Roger Stoltz12-Oct-05 1:53

Roger Stoltz

12-Oct-05 1:53

cauvang wrote:
convert a string from CString(MFC) to LPTSTR

Are you certain that your CString is an MFC CString?
I ask this because in the more detailed answer your gave toxcct here[^] looks like your using a CString defined in a namespace called 'WTL' which could indicate that it's all about the WTL version of CString you are using. I don't know anything about WTL so I won't be able to guide you there.

Check this out. If you're not using the MFC version our answers won't make sense.
Perhaps you even should post your question in the WTL forum.

--
Roger

cauvang12-Oct-05 15:21

12-Oct-05 15:21

I'm really sorry! I want to convert a string from CString(MFC) to LPCTSTR but the example is really stupid( it was written in WTL !!!).
Now I wonder how to use a WTL class ( written in WTL,used WTL CString ) in a MFC application. The class is so important and i need it in my MFC project.However,it was written in WTL using WTL CString.Help me!!

file handling

karmendra_js11-Oct-05 21:56

karmendra_js

11-Oct-05 21:56

i am saving some data to file(CStdio class) in the following format.

Address1-Description1
Address2-Description2
Address3-Description3

When ever i want to retrive data i search for the address and get the description.
Now when i change the description, it is required that i replace the old description with the new one.

One way is to re create the whole file again the only change of new description.
This is really inefficient.

Can you tell me some nice logic to do this

Thanks a lot

Bob Stanneveld11-Oct-05 22:53

Bob Stanneveld

11-Oct-05 22:53

Hello,

I don't think that it is possible to just 'insert' data in a file. When you write somewhere, data will be overwritten.

You have 2 options. You can insert buffers in the file (after an address, description, insert spaces). This way, you can overwrite the description and you have the option to grow until the specified buffer size.

The second option you have is to copy all the data after the description that you want to change and write it again after you update the description.

If you change the description frequently, I advice option 1. This is much faster. If the changes occurr less ofter and you have lot's of addresses, I suggest the second option. This saves you a lot of space, but it takes more time when you update your file.

Hope this helps.

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... is the police. - Conspiracy brother

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karmendra_js11-Oct-05 23:07

karmendra_js

11-Oct-05 23:07

thanks for your suggestions, still i have some things to clarify.

I have just 256 addresses so i will go with rewriting the file. But to do this i need to save the rest of the file temporarily, what do you think the data structure i have to use to do this.

Thanks again.

Bob Stanneveld12-Oct-05 6:14

Bob Stanneveld

12-Oct-05 6:14

Hello,

First, I assume that you are using MFC's CStdioFile class since I don't know of a CStdio class.

You can do the following:

// position after the line you want to change
// read all the adresses
CList<CString> StringList;
CString sLine = "";
while( YourFileObject.ReadString(sLine) )
{
    StringList.AddTail(sLine);
}

/*
    Change the address you want to change
    Place the file pointer after the changed address
*/
// write the other address back
while( !StringList.IsEmpty() )
{
    YourFileObject.WriteString(StringList.RemoveHead());
}

Hope this helps Big Grin | :-D

Behind every great black man...
... is the police. - Conspiracy brother

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