How to use random_shuffle with CString?

Question

I would like to shuffle the characters present in CString varible. How do i do it? Std provide a finction called random_shuffle() which can be used to shuffle std::string in the following way std::string s("ThisIsSample"); random_shuffle(s.first(),s.last()); But since CString doesnt have a function to access the fisrt and last character to iterate. How do i use random_shuffle with CString?

user4815162342 · Accepted Answer · 2014-11-29T20:33:36.020

2

Use GetBuffer to obtain the character buffer, and pass its boundaries to std::random_shuffle:

void shuffle_cstring(CString& c)
{
    size_t len = c.GetLength();
    LPTSTR buf = c.GetBuffer(1);
    std::random_shuffle(buf, buf + len);
    c.ReleaseBuffer();
}

edited Nov 29 '14 at 20:33

answered Nov 29 '14 at 08:13

user4815162342

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You need to call [`ReleaseBuffer`](http://msdn.microsoft.com/en-us/library/aa300574%28v=vs.60%29.aspx) when you're done with your manipulations. – Benjamin Lindley Nov 29 '14 at 08:21
Oh, and you should also call `GetLength` first, and store the result in a separate variable. Because you're not supposed to call any other member functions on the `CString` between the time you call `GetBuffer` and the time you call `ReleaseBuffer`. – Benjamin Lindley Nov 29 '14 at 08:26
@BenjaminLindley I wonder if that's really necessary in this case. MSDN says, *If you use the pointer returned by `GetBuffer` to change the string contents, you must call `ReleaseBuffer` before using any other CString member functions.* The code does change the contents, but only by rearranging characters, so it affects neither the length of the string nor the characters present. – user4815162342 Nov 29 '14 at 08:32
A shuffle is a series of swaps. A swap is 3 assignments (1 to an external character, and 2 to elements in the array). And an assignment is changing a character. Ergo, shuffling is changing the contents. You might be able to get away with it, but I don't see why you would unnecessarily break the contract of the API, knowing the implementation could change later on, possibly breaking your code. – Benjamin Lindley Nov 29 '14 at 08:37
@BenjaminLindley I agree that `std::random_shuffle` is changing the buffer contents. It is very questionable, however, that a character shuffle would affect `GetLength` in any way, especially as `GetLength` is required to work when the buffer remains unmodified. – user4815162342 Nov 29 '14 at 08:55

ravi · Answer 2 · 2014-11-29T08:12:00.337

Convert CString to std::string:-

CString cs("Hello");
std::string s((LPCTSTR)cs);

NOTE:- BUT: std::string cannot always construct from a LPCTSTR. i.e. the code 
will fail for UNICODE   builds.

EDIT IN RESPONSE TO COMMENT

As std::string can construct only from LPSTR / LPCSTR, a programmer who uses VC++ 7.x or better can utilize conversion classes such as CT2CA as an intermediary.

CString cs ("Hello");
// Convert a TCHAR string to a LPCSTR
CT2CA pszConvertedAnsiString (cs);
// construct a std::string using the LPCSTR input
std::string strStd (pszConvertedAnsiString);

Use random_shuffle on s and then:-

CString cs1(s.c_str());

Note that you can use `std::basic_string` to effectively get a `std::string` in narrow build and `std::wstring` in Unicode builds. — user4815162342, Nov 29 '14 at 09:06

How to use random_shuffle with CString?

2 Answers2