Thread: C/C++ - how use the GDIPLUS library?

Image.Image(const WCHAR*, BOOL) constructor (Windows)
Perhaps you need to consider UNICODE translation issues.

Originally Posted by Salem

Image.Image(const WCHAR*, BOOL) constructor (Windows)
Perhaps you need to consider UNICODE translation issues.

i did:

Code:

const size_t len = filename.length() + 1;
            wchar_t wcstring[len];
            swprintf(wcstring, len, L"%s", filename.c_str());

now i can convert string to wchar_t
now the code works:

Code:

hdcimage = CreateCompatibleDC(NULL);

            ULONG_PTR m_gdiplusToken;
            // Initialize GDI+
            Gdiplus::GdiplusStartupInput gdiplusStartupInput;
            Gdiplus::GdiplusStartup(&m_gdiplusToken, &gdiplusStartupInput, NULL);

            //Load the image from a file
            const size_t len = filename.length() + 1;
            wchar_t wcstring[len];
            swprintf(wcstring, len, L"%s", filename.c_str());

            Gdiplus::Image img (wcstring);
            HBITMAP hbitmap=CreateBitmap(img.GetWidth(),img.GetHeight(),1,32,NULL);
            SelectObject(hdcimage, hbitmap);
            Gdiplus::Graphics graphics(hdcimage); //Handle to the device context
            graphics.DrawImage(&img, 0, 0, img.GetWidth(), img.GetHeight());
            imageweight=img.GetWidth();
            imageheight=img.GetHeight();
            //Gdiplus::GdiplusShutdown(m_gdiplusToken);

the image is showed, but i see 2 problems:
1 - that comment line give me a memory leak(that's why is a comment). what i did wrong?
2 - why the image takes several seconds for be showed?
(in that time the wait\busy cursor is showed)

Originally Posted by joaquim

i did:

Code:

const size_t len = filename.length() + 1;
            wchar_t wcstring[len];
            swprintf(wcstring, len, L"%s", filename.c_str());

now i can convert string to wchar_t

Do absolutely not do that. The first issue that you are just doing a plain dumb widening of char -> wchar_t. But this is wrong. wchar_t is typically a different character set (often unicode). chars are typically ASCII or UTF-8, both of which cannot just be widened into a wchar_t. That will give you incorrect translation.
You need to do a proper conversion. Seeing as GDI is Windows, I'll give you these functions as a starting point for translating between different character sets (you will need to add an error class for throwing errors or change the code to handle errors):

Code:

	std::wstring AToU16(const std::string& From)
	{
		if (From.empty())
			return L"";
		auto Len = MultiByteToWideChar(CP_ACP, 0, From.data(), (int)From.size(), nullptr, 0);
		if (Len > 0)
		{
			std::wstring Str(Len, L'\0');
			MultiByteToWideChar(CP_ACP, 0, From.data(), (int)From.size(), &Str[0], Len);
			return Str;
		}
		throw stf::Errors::FailedToConvertString();
	}

	std::string U16ToU8(const std::wstring& From)
	{
		if (From.empty())
			return "";
		auto Len = WideCharToMultiByte(CP_UTF8, 0, From.data(), (int)From.size(), nullptr, 0, 0, 0);
		if (Len > 0)
		{
			std::string Str(Len, L'\0');
			WideCharToMultiByte(CP_UTF8, 0, From.data(), (int)From.size(), &Str[0], Len, 0, 0);
			return Str;
		}
		throw stf::Errors::FailedToConvertString();
	}

	std::wstring U8ToU16(const std::string& From)
	{
		if (From.empty())
			return L"";
		auto Len = MultiByteToWideChar(CP_UTF8, 0, From.data(), (int)From.size(), nullptr, 0);
		if (Len > 0)
		{
			std::wstring Str(Len, L'\0');
			MultiByteToWideChar(CP_UTF8, 0, From.data(), (int)From.size(), &Str[0], Len);
			return Str;
		}
		throw stf::Errors::FailedToConvertString();
	}

These functions convert between ASCII, UTF-8 and UTF-16 on Windows. char is typically ASCII on Windows unless you've explicitly converted it into UTF-8, so use AToU16.
Furthermore, do not use swprintf/sprintf. You will run into issues with buffer sizes.