why the changes not applied to the system in c

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my coding:

C++

#include "stdafx.h"
#include <windows.h>
#include <stdio.h>

int main(int argc, char* argv[])
{
	DEVMODE dm;
	ZeroMemory(&dm, sizeof(dm));
	
   dm.dmSize = sizeof(dm);
   int index = 0;
   if (0 != EnumDisplaySettings(NULL, ENUM_CURRENT_SETTINGS, &dm))
   {

	  DWORD dwTemp = dm.dmPelsHeight;
      dm.dmPelsHeight= 800;
      dm.dmPelsWidth = 600;
	  dm.dmDisplayFlags =  DM_DISPLAYFLAGS;
	  dm.dmBitsPerPel = 16;
	  dm.dmFields = 16;
	  if(DISP_CHANGE_SUCCESSFUL  == ChangeDisplaySettings(&dm,0))
	  {
		  printf("\nSuccess\n");
	  }
	  else
	  {
		  printf("\nFailure\n");
	  }
	  
	return 0;
}

i want to change the screen resolution..

The above program i wrote for that one..

But it produces success even-through the changes not applied to the screen ..

Why?

Posted 31-Oct-11 0:58am

@BangIndia

Updated 31-Oct-11 1:36am

Richard MacCutchan

v2

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Comments

Philippe Mori 31-Oct-11 18:22pm

Very bad idea for a program to change screen resolution. Your users will hate you!

2 solutions

Solution 2

Try this:

dm.dmFields = DM_PELSWIDTH Or DM_PELSHEIGHT Or DM_BITSPERPEL;

Good luck!

Posted 31-Oct-11 2:15am

E.F. Nijboer

Comments

@BangIndia 31-Oct-11 9:58am

while running the program the screen got rotated. i want to avoid the rotation. how.. i try to use dm.dmDisplayOrientation = DMDO_0 But it gives error: is not a member of '_devicemodeA'

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enhzflep · Accepted Answer · 2011-10-31T02:12:00

It seems that you've not fully specified which fields of DEVMODE are valid.

The value you set for flags is rather odd - 0x10 (corresponds to DM_SCALE)
You need to set a bit that indicates each of the valid fields of the structure.

Just change the line:

C++

dm.dmFields = 16;

To

C++

dm.dmFields = DM_BITSPERPEL | DM_PELSWIDTH | DM_PELSHEIGHT;

Oh! Also, do you mean to set a 600x800 screen (as shown in code) or the more likely 800x600? When I tried that, the bits/pixel changed, though the screen res didn't - I also received a success result. Guess the best thing to do is to check that the actual values are the expected ones after an attempt to change the screen settings..

C++

//#include "stdafx.h"
#include <windows.h>
#include <stdio.h>

int main(int argc, char* argv[])
{
	DEVMODE dm;
	ZeroMemory(&dm, sizeof(dm));

   dm.dmSize = sizeof(dm);
   int index = 0;
   if (0 != EnumDisplaySettings(NULL, ENUM_CURRENT_SETTINGS, &dm))
   {

	  DWORD dwTemp = dm.dmPelsHeight;
	  dm.dmPelsWidth = 800;
	  dm.dmPelsHeight= 600;
	  dm.dmDisplayFlags =  DM_DISPLAYFLAGS;
	  dm.dmBitsPerPel = 16;
	  dm.dmFields = DM_BITSPERPEL | DM_PELSWIDTH | DM_PELSHEIGHT;
	  if(DISP_CHANGE_SUCCESSFUL  == ChangeDisplaySettings(&dm,0))
	  {
		  printf("\nSuccess\n");
	  }
	  else
	  {
		  printf("\nFailure\n");
	  }
    }
    return 0;
}