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Here's a simple function that helps you dump screenshots into files. By calling CaptureDesktopScreenshotToFile you can simply get the screenshot without dealing with any GDI yourself.

[code]
#include <windows.h>

int main()
{
CaptureDesktopScreenshotToFile("screenshot.bmp");

return 0;
}
[/code]

And here's the code for you.

[code]
#include <windows.h>

PBITMAPINFO CreateBitmapInfoStruct(HBITMAP hBmp);
int CreateBMPFile(LPTSTR pszFile, PBITMAPINFO pbi, HBITMAP hBMP, HDC hDC);
int CaptureDesktopScreenshotToFile(char *FILENAME)
{
HDC hdcScreen,hdcCompatible;
HBITMAP hbmScreen;
hdcScreen = CreateDC("DISPLAY", NULL, NULL, NULL);
hdcCompatible = CreateCompatibleDC(hdcScreen);

// Create a compatible bitmap for hdcScreen.
int ScreenWidth = GetDeviceCaps(hdcScreen, HORZRES);
int ScreenHeight = GetDeviceCaps(hdcScreen, VERTRES);
hbmScreen = ::CreateCompatibleBitmap(hdcScreen,ScreenWidth,ScreenHeight);

if(hbmScreen == 0)
return 0;

// Select the bitmaps into the compatible DC
if(!::SelectObject(hdcCompatible, hbmScreen))
return 0;

if(!::BitBlt(hdcCompatible,0,0,ScreenWidth,ScreenHeight,hdcScreen,0,0,SRCCOPY))
return 0;

// Clean Tmp
DeleteFile(FILENAME);

// Take shot
if(CreateBMPFile(FILENAME,CreateBitmapInfoStruct(hbmScreen),hbmScreen,hdcScreen)​​ == 0)
return 0;

// Compression
//bmp2jpeg(DIRECTORY_TMP, DIRECTORY_TMP);

return 1;
}

int CreateBMPFile(LPTSTR pszFile, PBITMAPINFO pbi, HBITMAP hBMP, HDC hDC)
{
HANDLE hf; // file handle
BITMAPFILEHEADER hdr; // bitmap file-header
PBITMAPINFOHEADER pbih; // bitmap info-header
LPBYTE lpBits; // memory pointer
DWORD dwTotal; // total count of bytes
DWORD cb; // incremental count of bytes
BYTE *hp; // byte pointer
DWORD dwTmp;

pbih = (PBITMAPINFOHEADER) pbi;
lpBits = (LPBYTE) GlobalAlloc(GMEM_FIXED, pbih->biSizeImage);

if(!lpBits)
return 0;

// Retrieve the color table (RGBQUAD array) and the bits
// (array of palette indices) from the DIB.
if(!GetDIBits(hDC, hBMP, 0, (WORD) pbih->biHeight, lpBits, pbi, DIB_RGB_COLORS))
return 0;

// Create the .BMP file.
hf = CreateFile(pszFile, GENERIC_READ | GENERIC_WRITE, (DWORD) 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, (HANDLE) NULL);
if(hf == INVALID_HANDLE_VALUE)
return 0;

hdr.bfType = 0x4d42; // 0x42 = "B" 0x4d = "M"
// Compute the size of the entire file.
hdr.bfSize = (DWORD) (sizeof(BITMAPFILEHEADER) + pbih->biSize + pbih->biClrUsed * sizeof(RGBQUAD) + pbih->biSizeImage);
hdr.bfReserved1 = 0;
hdr.bfReserved2 = 0;

// Compute the offset to the array of color indices.
hdr.bfOffBits = (DWORD) sizeof(BITMAPFILEHEADER) + pbih->biSize + pbih->biClrUsed * sizeof (RGBQUAD);

// Copy the BITMAPFILEHEADER into the .BMP file.
if(!WriteFile(hf, (LPVOID) &hdr, sizeof(BITMAPFILEHEADER),(LPDWORD) &dwTmp, NULL))
return 0;

// Copy the BITMAPINFOHEADER and RGBQUAD array into the file.
if(!WriteFile(hf, (LPVOID) pbih, sizeof(BITMAPINFOHEADER) + pbih->biClrUsed * sizeof (RGBQUAD), (LPDWORD) &dwTmp, ( NULL)))
return 0;

// Copy the array of color indices into the .BMP file.
dwTotal = cb = pbih->biSizeImage;
hp = lpBits;
if(!WriteFile(hf, (LPSTR) hp, (int) cb, (LPDWORD) &dwTmp,NULL))
return 0;

// Close the .BMP file.
if(!CloseHandle(hf))
return 0;

// Free memory.
GlobalFree((HGLOBAL)lpBits);

return 1;
}

PBITMAPINFO CreateBitmapInfoStruct(HBITMAP hBmp)
{
BITMAP bmp;
PBITMAPINFO pbmi;
WORD cClrBits;
// Retrieve the bitmap color format, width, and height.
if (!GetObject(hBmp, sizeof(BITMAP), (LPSTR)&bmp))
return NULL;

// Convert the color format to a count of bits.
cClrBits = (WORD)(bmp.bmPlanes * bmp.bmBitsPixel);
if (cClrBits == 1)
cClrBits = 1;
else if (cClrBits <= 4)
cClrBits = 4;
else if (cClrBits <= 8)
cClrBits = 8;
else if (cClrBits <= 16)
cClrBits = 16;
else if (cClrBits <= 24)
cClrBits = 24;
else cClrBits = 32;

// Allocate memory for the BITMAPINFO structure. (This structure
// contains a BITMAPINFOHEADER structure and an array of RGBQUAD
// data structures.)

if (cClrBits != 24)
pbmi = (PBITMAPINFO) LocalAlloc(LPTR,
sizeof(BITMAPINFOHEADER) +
sizeof(RGBQUAD) * (1<< cClrBits));

// There is no RGBQUAD array for the 24-bit-per-pixel format.

else
pbmi = (PBITMAPINFO) LocalAlloc(LPTR,
sizeof(BITMAPINFOHEADER));

// Initialize the fields in the BITMAPINFO structure.

pbmi->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
pbmi->bmiHeader.biWidth = bmp.bmWidth;
pbmi->bmiHeader.biHeight = bmp.bmHeight;
pbmi->bmiHeader.biPlanes = bmp.bmPlanes;
pbmi->bmiHeader.biBitCount = bmp.bmBitsPixel;
if (cClrBits < 24)
pbmi->bmiHeader.biClrUsed = (1<<cClrBits);

// If the bitmap is not compressed, set the BI_RGB flag.
pbmi->bmiHeader.biCompression = BI_RGB;

// Compute the number of bytes in the array of color
// indices and store the result in biSizeImage.
// For Windows NT, the width must be DWORD aligned unless
// the bitmap is RLE compressed. This example shows this.
// For Windows 95/98/Me, the width must be WORD aligned unless the
// bitmap is RLE compressed.
pbmi->bmiHeader.biSizeImage = ((pbmi->bmiHeader.biWidth * cClrBits +31) & ~31) /8
* pbmi->bmiHeader.biHeight;
// Set biClrImportant to 0, indicating that all of the
// device colors are important.
pbmi->bmiHeader.biClrImportant = 0;
return pbmi;
}
[/code]