使用向量 <wchar> 而不是动态分配的wchar数组

Question

The other day, I got told off (on stackoverflow!) for not using vector instead of a dynamically allocated wchar array.

So I had a look into using this method of string manipulation, as it seems like a good idea to prevent possible memory leaks.

What I came up with was, that unless I'm using the vector template class incorrectly, using vector is much less flexible than using a heap allocated array and good old memcpy.

#include <shlobj.h>
HRESULT ModifyTheme()
{
using namespace std;

vector <WCHAR>  sOutput;
vector <WCHAR>  sPath;      
vector <WCHAR>  sThemesLocation;
vector <WCHAR>  sThemeName; 

const WCHAR sThemesPath []  = _T("\\Microsoft\\Windows\\Themes");
const WCHAR sFileName []    = _T("\\darkblue.theme");

sOutput.resize(MAX_PATH);
sPath.resize( MAX_PATH );   
sThemesLocation.resize( MAX_PATH );
sThemeName.resize( MAX_PATH );

// Get appdata\local folder
SHGetFolderPath(NULL, CSIDL_LOCAL_APPDATA, NULL, 0, &sPath[0] );

// copy consts to vectors   
memcpy( &sThemesLocation[0],    sThemesPath,    sizeof(sThemesPath) );
memcpy( &sThemeName[0],         sFileName,      sizeof(sFileName) );    

// append themes path & filename
sOutput.insert( sOutput.begin(), sPath.begin(), sPath.end() );
sOutput.insert( sOutput.end()-1, sThemesLocation.begin(), sThemesLocation.end() );
sOutput.insert( sOutput.end()-1, sThemeName.begin(), sThemeName.end() );    

wcout << &sThemeName[0] << endl;
wcout << &sThemesLocation[0] << endl;
wcout << &sPath[0] << endl;
wcout << &sOutput[0] << endl;

return S_OK;
}

I'd expect the sOutput vector to contain a concatenation of all strings. Instead, it only contains the first inserted string.

Also, I think I remember hearing that although it's not possible to assign a vector's values in an initializer list, it may be a feature of c++0x. Is this correct - and is there any way (at the minute) to do the following:

vector<wchar> sBleh = { _T("bleh") };

Finally, for what I want to achive with the simple routine above, would I be better with a dynamically allocated array, or should I persist with the seemingly inflexible vector of wchar?

Answer 1

If you're using std::vector<WCHAR> you should probably be using std::wstring as it is also a container of WCHAR elements.

The following links might help you:
std::wstring (typedef of std::basic_string<WCHAR> )
std::basic_string

Answer 2

Use the best tool for the job. Some situations call for using static arrays and some for dynamic arrays. When the situation calls for a dynamic array, use a vector instead.

Mark Ingram is correct that you could use wstring, but only if wchar_t is the same size as WCHAR.

Something like this is better for what you want (note, I didn't run the below through a compiler because there are too many Microsoft specific constructs.):

WCHAR sPath[MAX_PATH]; // doesn't need to be a dynamic array, so don't bother with a vector.
SHGetFolderPath(NULL, CSIDL_LOCAL_APPDATA, NULL, 0, &sPath[0] );

const WCHAR sThemesPath[] = _T("\\Microsoft\\Windows\\Themes"); // doesn't need to be a dynamic array, so don't bother with a vector.
const WCHAR sFileName[] = _T("\\darkblue.theme"); // doesn't need to be a dynamic array, so don't bother with a vector.
vector<WCHAR> sOutput; // this needs to be dynamic so use a vector.

// wcslen should probably be replaced with an MS specific call that gets the length of a WCHAR string
copy(sPath, sPath + wcslen(sPath), back_inserter(sOutput));
copy(sThemesPath, sThemesPath + wcslen(sThemesPath), back_inserter(sOutput));
copy(sFlieName, sFileName + wcslen(sFileName), back_inserter(sOutput));