Question

Working on a Windows 7 servicepack 1 environment with cygwin gcc compiler.

The following program is supposed to take a screenshot and save the file as a .bmp to the file specified. It compiles fine and seems to give a .bmp file in the desired directory but when run seems to create only a 1kb file with no screenshot data in it. If the while loop is given a starting value of while(1), it gives the “Unable to Create Bitmap File” error. I am new to this kind of programming and cannot seem to see why this is.

Any ideas?

(has to be compiled with -lgdi32)

code:

#include <stdlib.h>
#include <windows.h>
#include <stdio.h>

void TakeScreenShot(char* filename);

int main()
{
   TakeScreenShot("c:\\Screenshot.bmp");
   return 0;
}

//
// Side Effects:N/A
//
//This code is copyrighted and has// limited warranties.Please see http://
//   www.Planet-Source-Code.com/vb/scripts/Sh
//   owCode.asp?txtCodeId=10754&lngWId=3//for details.//**************************************
// 

void TakeScreenShot(char* filename)
{
   keybd_event(VK_SNAPSHOT, 0x45, KEYEVENTF_EXTENDEDKEY, 0);
   keybd_event(VK_SNAPSHOT, 0x45, KEYEVENTF_EXTENDEDKEY | KEYEVENTF_KEYUP, 0);
   HBITMAP h;        

   OpenClipboard(NULL);
   h = (HBITMAP)GetClipboardData(CF_BITMAP);
   CloseClipboard();
   HDC hdc=NULL;

   FILE*fp=NULL;
   LPVOID pBuf=NULL;
   BITMAPINFO bmpInfo;
   BITMAPFILEHEADER bmpFileHeader;

   do
   {
      hdc=GetDC(NULL);
      ZeroMemory(&bmpInfo,sizeof(BITMAPINFO));
      bmpInfo.bmiHeader.biSize=sizeof(BITMAPINFOHEADER);
      GetDIBits(hdc,h,0,0,NULL,&bmpInfo,DIB_RGB_COLORS);

      if(bmpInfo.bmiHeader.biSizeImage<=0)
         bmpInfo.bmiHeader.biSizeImage=bmpInfo.bmiHeader.biWidth*abs(bmpInfo.bmiHeader.biHeight)*(bmpInfo.bmiHeader.biBitCount+7)/8;
      if((pBuf = malloc(bmpInfo.bmiHeader.biSizeImage))==NULL)
      {
         MessageBox( NULL, "Unable to Allocate Bitmap Memory", "Error", MB_OK|MB_ICONERROR);
         break;
      }
      bmpInfo.bmiHeader.biCompression=BI_RGB;
      GetDIBits(hdc,h,0,bmpInfo.bmiHeader.biHeight,pBuf, &bmpInfo, DIB_RGB_COLORS);

      if((fp = fopen(filename,"wb"))==NULL)
      {
         MessageBox(NULL, "Unable to Create Bitmap File", "Error", MB_OK|MB_ICONERROR);
         break;
      }

      bmpFileHeader.bfReserved1=0;
      bmpFileHeader.bfReserved2=0;
      bmpFileHeader.bfSize=sizeof(BITMAPFILEHEADER)+sizeof(BITMAPINFOHEADER)+bmpInfo.bmiHeader.biSizeImage;
      bmpFileHeader.bfType='MB';
      bmpFileHeader.bfOffBits=sizeof(BITMAPFILEHEADER)+sizeof(BITMAPINFOHEADER);

      fwrite(&bmpFileHeader,sizeof(BITMAPFILEHEADER),1,fp);
      fwrite(&bmpInfo.bmiHeader,sizeof(BITMAPINFOHEADER),1,fp);
      fwrite(pBuf,bmpInfo.bmiHeader.biSizeImage,1,fp);
   }
   while(0);

   if(hdc)
      ReleaseDC(NULL,hdc);

   if(pBuf)
      free(pBuf);

   if(fp)
      fclose(fp);
}

Answer 1

The program apparently saves bitmap data it gets from the clipboard. If there is no data on the clipboard, I assume it only saves an empty bitmap. And it writes a file called “Screenshot.bmp”, not a .png file.

To put bitmap data on the clipboard, I assume you must press the print screen button first. This saves a screenshot to the clipboard. Now the program can be used to save this clipboard data to a file.