Create a new string from an old one

Question

I'm using C++ (Windows environment). I have a :

LPCWSTR mystring;

This works :

mystring = TEXT("Hello");

But how to do this ? :

mystring = ((((create a new string with text = the content which is in another LPCWSTR 'myoldstring'))))

Thanks a lot in advance!

PS :

mystring = myoldstring;

would work , but it would not create a new string, it would be the same pointer. I want to create a new string !

Jerry Coffin · Answer 1 · 2012-12-09T15:05:22.140

2

To use C++ standard strings, you need to include the <string> header. Since you're dealing with LPCWSTR (emphasis on the W part of that) you're dealing with wide characters, so you want to use wide strings (i.e., std::wstring instead of std::string).

#include <string>
#include <iostream>
#include <windows.h>

int main() { 
    LPCWSTR x=L"This is a string";

    std::wstring y = x;
    std::wcout << y;
}

edited Dec 09 '12 at 15:05

answered Dec 09 '12 at 14:50

Jerry Coffin

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I don't know why, but with this solution, there is crash ! – Basj Dec 09 '12 at 14:58
@JosBas: That would point to a problem with the standard library you're using, or somewhere else in your code. Of the two, a problem elsewhere in your code seems a lot more likely to me. I've edited in a slightly more complete example that should compile and display the copied string (it does for me anyway). If it works, your problem is probably elsewhere in your code. – Jerry Coffin Dec 09 '12 at 15:04
If I remove this line, no crash. If I add it, there is a crash. I have used another variable names that are used *nowhere else*, such that the crash cannot come from anywhere else. – Basj Dec 09 '12 at 15:10
1

@JosBas: That sounds like fairly typical results from having undefined behavior: some seemingly unrelated change suddenly leads to a crash. Without seeing your other code, it's impossible to guess where it might have come from though. Of course, it *is* always possible your standard library is defective -- `std::wstring` probably isn't nearly as well tested as `std::string` (but it's still much more likely the problem is in your code). – Jerry Coffin Dec 09 '12 at 15:16

user93353 · Accepted Answer · 2012-12-09T15:17:16.007

2

LPTSTR mystring;
mystring = new TCHAR[_tcslen(oldstring) + 1];
_tcscpy(mystring, oldstring);

... After you are done ...

delete [] mystring;

This is a complete program

#include <tchar.h>
#include <windows.h>
#include <string.h>

int main()
{
    LPCTSTR oldstring = _T("Hello");

    LPTSTR mystring;
    mystring = new TCHAR[_tcslen(oldstring) + 1];
    _tcscpy(mystring, oldstring);

    // Stuff

    delete [] mystring;


}

It compiles fine with cl /DUNICODE /D_UNICODE a.cpp

I used tchar macros. If you don't want to use it, then

#include <windows.h>
#include <string.h>

int main()
{
    LPCWSTR oldstring = L"Hello";

    LPWSTR mystring;
    mystring = new WCHAR[wcslen(oldstring) + 1];
    wcscpy(mystring, oldstring);

    // Stuff

    delete [] mystring;


}

Compiles fine with cl a.cpp

edited Dec 09 '12 at 15:17

answered Dec 09 '12 at 14:55

user93353

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`error C2440: '=' : impossible de convertir de 'LPCWSTR *' en 'LPCWSTR'` I am very very unlucky today ! – Basj Dec 09 '12 at 15:01
@JosBas small error in my code - Corrected it - won't give this error. – user93353 Dec 09 '12 at 15:02
the line with new LPCWSTR ! – Basj Dec 09 '12 at 15:03
An error again :( : `error C2664: 'wcscpy' : impossible de convertir le paramètre 1 de 'LPCWSTR' en 'wchar_t *'` – Basj Dec 09 '12 at 15:08
Did you do the 2nd change I have indicated - mystring should be `LPTSTR` or `LPWSTR` not `LPCWSTR` – user93353 Dec 09 '12 at 15:10

score 0 · Answer 3 · answered Dec 09 '12 at 14:33

0

what about

string myNewString = std::string(myOldString);

Just using the copy constructor of the string library.

answered Dec 09 '12 at 14:33

cowboydan

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`'string' : identificateur introuvable !` (Can't find `string`) I use C++ (no .NET ) – Basj Dec 09 '12 at 14:39
@JosBas `#include ` ... and then make sure the `std` namespace is properly used, either though prefixing (`std::string` was omitted in one of the two cases above) or through `using namespace std;`. – Branko Dimitrijevic Dec 09 '12 at 14:58

Create a new string from an old one

3 Answers3