Change wallpaper programmatically using c++ and windows api - c++

Question

I've been trying to write an application, using Qt and mingw32, to download images and set them as the background Wallpaper. I have read several articles online about how to do this, in VB and C#, and to some extent how to do it in c++. I am currently calling the SystemParametersInfo with what seems to be all the correct arguments (no compiler errors) and it fails. No great crash of cymbals, just a 0 returned. GetLastError() returns an equally enlightening 0.
Below is the code I am using (In a slightly modified form, so you do not have to view the object internals).
#include <windows.h>
#include <iostream>
#include <QString>
void setWall()
{
QString filepath = "C:\\Documents and Settings\\Owner\\My Documents\\Wallpapers\\wallpaper.png";
char path[150];
strcpy(path, currentFilePath.toStdString().c_str());
char *pathp;
pathp = path;
cout << path;
int result;
result = SystemParametersInfo(SPI_SETDESKWALLPAPER, 0, pathp, SPIF_UPDATEINIFILE);
if (result)
{
cout << "Wallpaper set";
}
else
{
cout << "Wallpaper not set";
cout << "SPI returned" << result;
}
}

Answer 1

It could be that SystemParametersInfo is expecting an LPWSTR (a pointer to wchar_t).
Try this:
LPWSTR test = L"C:\\Documents and Settings\\Owner\\My Documents\\Wallpapers\\wallpaper.png";
result = SystemParametersInfo(SPI_SETDESKWALLPAPER, 0, test, SPIF_UPDATEINIFILE);
If this works (try it with a few different files just to make sure), you'll need to convert your char * to a LPWSTR. I'm not sure if Qt offers these services, but one function that may help is MultiByteToWideChar.

Answer 2

"C:\Documents and Settings\Owner\My Documents\Wallpapers\wallpaper.png";
shouldn't this be:
"C:\\Documents and Settings\\Owner\\My Documents\\Wallpapers\\wallpaper.png";

Answer 3

You cn use SetTimer to trigger a change.
#define STRICT 1
#include <windows.h>
#include <iostream.h>
VOID CALLBACK TimerProc(HWND hWnd, UINT nMsg, UINT nIDEvent, DWORD dwTime)
{
LPWSTR wallpaper_file = L"C:\\Wallpapers\\wallpaper.png";
int return_value = SystemParametersInfo(SPI_SETDESKWALLPAPER, 0, wallpaper_file, SPIF_UPDATEINIFILE);
cout << "Programmatically change the desktop wallpaper periodically: " << dwTime << '\n';
cout.flush();
}
int main(int argc, char *argv[], char *envp[])
{
int Counter=0;
MSG Msg;
UINT TimerId = SetTimer(NULL, 0, 2000, &TimerProc); //2000 milliseconds
cout << "TimerId: " << TimerId << '\n';
if (!TimerId)
return 16;
while (GetMessage(&Msg, NULL, 0, 0))
{
++Counter;
if (Msg.message == WM_TIMER)
cout << "Counter: " << Counter << "; timer message\n";
else
cout << "Counter: " << Counter << "; message: " << Msg.message << '\n';
DispatchMessage(&Msg);
}
KillTimer(NULL, TimerId);
return 0;
}