Program gets stuck after taking screenshot - c++

Question

#include "screenshot.h"
#include "changewallpaper.h"
using namespace std;
int main()
{
screenshot();
changewallpaper();
}
My screenshot();
#include <windows.h>
#include <gdiplus.h>
#include <stdio.h>
using namespace Gdiplus;
int GetEncoderClsid(const WCHAR* format, CLSID* pClsid)
{
UINT num = 0; // number of image encoders
UINT size = 0; // size of the image encoder array in bytes
ImageCodecInfo* pImageCodecInfo = NULL;
GetImageEncodersSize(&num, &size);
if(size == 0)
return -1; // Failure
pImageCodecInfo = (ImageCodecInfo*)(malloc(size));
if(pImageCodecInfo == NULL)
return -1; // Failure
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; // Success
}
}
free(pImageCodecInfo);
return -1; // Failure
}
void screenshot()
{
// get the device context of the screen
HDC hScreenDC = CreateDC("DISPLAY", NULL, NULL, NULL);
int width = GetDeviceCaps(hScreenDC, HORZRES);
int height = GetDeviceCaps(hScreenDC, VERTRES);
POINT a,b;
a.x=0;
a.y=0;
b.x=width;
b.y=height;
// copy screen to bitmap
HDC hScreen = GetDC(NULL);
HDC hDC = CreateCompatibleDC(hScreen);
HBITMAP hBitmap = CreateCompatibleBitmap(hScreen, abs(b.x-a.x), abs(b.y-a.y));
HGDIOBJ old_obj = SelectObject(hDC, hBitmap);
BOOL bRet = BitBlt(hDC, 0, 0, abs(b.x-a.x), abs(b.y-a.y), hScreen, a.x, a.y, SRCCOPY);
//Initialize GDI+
GdiplusStartupInput gdiplusStartupInput;
ULONG_PTR gdiplusToken;
GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);
Gdiplus::Bitmap bitmap(hBitmap, NULL);
CLSID pngClsid;
GetEncoderClsid(L"image/png", &pngClsid);
bitmap.Save(L"D:\\Pictures\\screen.png", &pngClsid, NULL);
// clean up
SelectObject(hDC, old_obj);
DeleteDC(hDC);
ReleaseDC(NULL, hScreen);
DeleteObject(hBitmap);
//delete image;
GdiplusShutdown(gdiplusToken);
}
My problem is that changewallpaper(); never runs. If I place changewallpaper(); before screenshot(); in my main everything works but not if I have it like above. I need my program to take the screenshot before it changes the wallpaper so I can't just switch them. Does anyone know what might be the problem? I am clueless.

Answer 1

As #xsoftie, You are hanging in the image::~image().
According to the GdiplusShutdown :
you must delete all of your GDI+ objects (or have them go out of
scope) before you call GdiplusShutdown.
Gdiplus::Bitmap bitmap(hBitmap, NULL);
bitmap are stored on the stack, and the system automatically releases them at the end of their life cycle (after {}). scoftie's method is one of feasible solutions.
Of course you can also use new to request GDI + object pointers on the heap, as this sample:
Gdiplus::Bitmap *bitmap = new Gdiplus::Bitmap(hBitmap, NULL);
CLSID pngClsid;
GetEncoderClsid(L"image/png", &pngClsid);
bitmap->Save(L"D:\\Pictures\\screen.png", &pngClsid, NULL);
//...
delete bitmap;
GdiplusShutdown(gdiplusToken);
Or, put GdiplusStartup and GdiplusShutdown in the main function:
int main()
{
GdiplusStartupInput gdiplusStartupInput;
ULONG_PTR gdiplusToken;
GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);
screenshot();
changewallpaper();
GdiplusShutdown(gdiplusToken);
}
And in addition, When you no longer need the hScreenDC, call the DeleteDC function.

Answer 2

A couple changes. The scoping is necessary to get the bitmap out of scope and clean up after itself. The second is releasing the hScreenDC although I'll leave that as an exercise for you to see if it is necessary. You were hanging in the image::~image function. Let me know if it fixes it for you.
{
Gdiplus::Bitmap bitmap(hBitmap, NULL);
CLSID pngClsid;
GetEncoderClsid(L"image/png", &pngClsid);
bitmap.Save(L"c:\\temp\\screen.png", &pngClsid, NULL);
}
// clean up
SelectObject(hDC, old_obj);
DeleteDC(hDC);
ReleaseDC(NULL, hScreen);
DeleteObject(hBitmap);
DeleteDC(hScreenDC);