Take a screenshot and save as jpeg in c++

screenshot.cpp

#include <stdio.h>
#include <windows.h>
#include <gdiplus.h>
#include <time.h>

int GetEncoderClsid(const WCHAR* format, CLSID* pClsid) {
	using namespace Gdiplus;
	UINT  num = 0;
	UINT  size = 0;

	ImageCodecInfo* pImageCodecInfo = NULL;

	GetImageEncodersSize(&num, &size);
	if(size == 0)
		return -1;

	pImageCodecInfo = (ImageCodecInfo*)(malloc(size));
	if(pImageCodecInfo == NULL)
		return -1;

	GetImageEncoders(num, size, pImageCodecInfo);
	for(UINT j = 0; j < num; ++j)
	{
		if( wcscmp(pImageCodecInfo[j].MimeType, format) == 0 )
		{
			*pClsid = pImageCodecInfo[j].Clsid;
			free(pImageCodecInfo);
			return j;
		}    
	}
	free(pImageCodecInfo);
	return 0;
}

void gdiscreen() {
	using namespace Gdiplus;
	IStream* istream;
	HRESULT res = CreateStreamOnHGlobal(NULL, true, &istream);
	GdiplusStartupInput gdiplusStartupInput;
	ULONG_PTR gdiplusToken;
	GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);
	{
		HDC scrdc, memdc;
		HBITMAP membit;
		scrdc = ::GetDC(0);
		int Height = GetSystemMetrics(SM_CYSCREEN);
		int Width = GetSystemMetrics(SM_CXSCREEN);
		memdc = CreateCompatibleDC(scrdc);
		membit = CreateCompatibleBitmap(scrdc, Width, Height);
		HBITMAP hOldBitmap =(HBITMAP) SelectObject(memdc, membit);
		BitBlt(memdc, 0, 0, Width, Height, scrdc, 0, 0, SRCCOPY);
		
		Gdiplus::Bitmap bitmap(membit, NULL);
		CLSID clsid;
		GetEncoderClsid(L"image/jpeg", &clsid);
//		bitmap.Save(L"screen.jpeg", &clsid, NULL); // To save the jpeg to a file
		bitmap.Save(istream, &clsid, NULL);
		
		// Create a bitmap from the stream and save it to make sure the stream has the image
//		Gdiplus::Bitmap bmp(istream, NULL);
//		bmp.Save(L"t1est.jpeg", &clsid, NULL);             
		// END
		
		delete &clsid;
		DeleteObject(memdc);
		DeleteObject(membit);
		::ReleaseDC(0,scrdc);
	}
	GdiplusShutdown(gdiplusToken);
}

int main()
{
    	clock_t t1 = clock();
	int i;
	int iterations = 10;
	for(i=0;i<iterations;i++){
		gdiscreen();
	}
	clock_t t2 = clock();
	printf("%d iterations: %0.0f fps\n", iterations, iterations/((double)(t2 - t1) / CLOCKS_PER_SEC));
    	return 0;
}

One should import gdiplus.lib in their project before compiling. If you are on windows/Visual-studio, you should include this in your source file
#pragma comment (lib, "gdiplus.lib")
OR
You could add the above lib in the VS Project like below
Project Properties > Linker > input > Additional Dependencies

Plus as stated by haephrati; remove delete &clsid;

In order to write the jpeg file; you had to uncomment the below line to save the jpeg image in the appropriate location i.e.

bitmap.Save(path/to/jpeg, &clsid, NULL);

i spent time to find out how to start it working. so i did. on windows 7. to right code is:

#include <stdio.h>
#include <windows.h>
#include <gdiplus.h>
#include <time.h>
#include <cstdio>
#pragma comment (lib, "gdiplus.lib")

int GetEncoderClsid(const WCHAR* format, CLSID* pClsid) {
	using namespace Gdiplus;
	UINT  num = 0;
	UINT  size = 0;

	ImageCodecInfo* pImageCodecInfo = NULL;

	GetImageEncodersSize(&num, &size);
	if(size == 0)
		return -1;

	pImageCodecInfo = (ImageCodecInfo*)(malloc(size));
	if(pImageCodecInfo == NULL)
		return -1;

	GetImageEncoders(num, size, pImageCodecInfo);
	for(UINT j = 0; j < num; ++j)
	{
		if( wcscmp(pImageCodecInfo[j].MimeType, format) == 0 )
		{
			*pClsid = pImageCodecInfo[j].Clsid;
			free(pImageCodecInfo);
			return j;
		}    
	}
	free(pImageCodecInfo);
	return 0;
}

void gdiscreen() {
	using namespace Gdiplus;
	IStream* istream;
	HRESULT res = CreateStreamOnHGlobal(NULL, true, &istream);
	GdiplusStartupInput gdiplusStartupInput;
	ULONG_PTR gdiplusToken;
	GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);
	{
		HDC scrdc, memdc;
		HBITMAP membit;
		scrdc = ::GetDC(0);
		int Height = GetSystemMetrics(SM_CYSCREEN);
		int Width = GetSystemMetrics(SM_CXSCREEN);
		memdc = CreateCompatibleDC(scrdc);
		membit = CreateCompatibleBitmap(scrdc, Width, Height);
		HBITMAP hOldBitmap =(HBITMAP) SelectObject(memdc, membit);
		BitBlt(memdc, 0, 0, Width, Height, scrdc, 0, 0, SRCCOPY);
		
		Gdiplus::Bitmap bitmap(membit, NULL);
		CLSID clsid;
		GetEncoderClsid(L"image/jpeg", &clsid);
		bitmap.Save(L"screen.jpeg", &clsid, NULL); // To save the jpeg to a file
		bitmap.Save(istream, &clsid, NULL);
		
		// Create a bitmap from the stream and save it to make sure the stream has the image
//		Gdiplus::Bitmap bmp(istream, NULL);
//		bmp.Save(L"t1est.jpeg", &clsid, NULL);             
		// END
		
		//delete &clsid;
		DeleteObject(memdc);
		DeleteObject(membit);
		::ReleaseDC(0,scrdc);
	}
	GdiplusShutdown(gdiplusToken);
}

int main()
{
    	clock_t t1 = clock();
	int i;
	int iterations = 10;
	for(i=0;i<iterations;i++){
		gdiscreen();
	}
	clock_t t2 = clock();
	printf("%d iterations: %0.0f fps\n", iterations, iterations/((double)(t2 - t1) / CLOCKS_PER_SEC));
    	return 0;
}

but if you compile it with :
gcc screenshot.cpp -o out.exe -lgdiplus -mwindows -lole32
it gives error:
undefined reference to __gxx_personality_v0' ...
so the right command to compile it is :
gcc screenshot.cpp -o out.exe -lgdiplus -mwindows -lole32 -static-libgcc -Wl,-Bstatic -lstdc++

have a nice day!

Saving screenshot into a byte array:

std::vector<unsigned char> GetScreenshot() {
	IStream* istream;
	HRESULT res = CreateStreamOnHGlobal(NULL, true, &istream);
	Gdiplus::GdiplusStartupInput gdiplusStartupInput;
	ULONG_PTR gdiplusToken;
	GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);

	HDC scrdc, memdc;
	HBITMAP membit;
	scrdc = ::GetDC(0);
	int Height = GetSystemMetrics(SM_CYSCREEN);
	int Width = GetSystemMetrics(SM_CXSCREEN);
	memdc = CreateCompatibleDC(scrdc);
	membit = CreateCompatibleBitmap(scrdc, Width, Height);
	HBITMAP hOldBitmap = (HBITMAP)SelectObject(memdc, membit);
	BitBlt(memdc, 0, 0, Width, Height, scrdc, 0, 0, SRCCOPY);

	Gdiplus::Bitmap bitmap(membit, NULL);
	CLSID clsid;
	GetEncoderClsid(L"image/jpeg", &clsid);

	bitmap.Save(istream, &clsid, NULL);

	STATSTG statstg;
	istream->Stat(&statstg, STATFLAG_NONAME);
	ULARGE_INTEGER uliSize = statstg.cbSize;

	// Allocate buffer and read the stream into it
	std::vector<unsigned char> buffer(uliSize.LowPart);
	LARGE_INTEGER liZero = {};
	istream->Seek(liZero, STREAM_SEEK_SET, NULL);
	ULONG bytesRead;
	istream->Read(buffer.data(), uliSize.LowPart, &bytesRead);

	return buffer;
}