UpdateResource

Introduction

Over the years, I've seen various flavors of the question "How do I include a file or data with my program that I can extract at run-time and do something with it?" For example, the asker might have had a .WAV file or a .MDB (MS Access) file that s/he wanted to include in the actual executable itself. For one reason or another, they do not want to package the two files separately. One advantage this has over a separate data/configuration file is that it'll never get lost. If the user decides they want to start fresh, they can remove everything but the application itself, and when the application is started up again, it extracts an empty database, all without the user knowing the behind-the-scenes details.

So thre are really two questions on the table here: "How to include the file?" and "Once the file is included, how to extract it and 'use' it?" Let's look at a simple example.

Including the file

In this example, I'll show the necessary code to take the entire Windows calculator (calc.exe) and add it as a resource to some test .EXE. The .EXE could just as easily be the application where these code snippets reside. The first thing we must do is open calc.exe in read-only mode, and read the entire file into a buffer.

HANDLE hFile;
DWORD dwFileSize,      
      dwBytesRead;
LPBYTE lpBuffer;

hFile = CreateFile(L"C:\\Winnt\\System32\\calc.exe", GENERIC_READ, 
                   0,
                   NULL,
                   OPEN_EXISTING,
                   FILE_ATTRIBUTE_NORMAL,
                   NULL);

if (INVALID_HANDLE_VALUE != hFile)
{
    dwFileSize = GetFileSize(hFile, NULL);

    lpBuffer = new BYTE[dwFileSize];

    if (ReadFile(hFile, lpBuffer, dwFileSize, &dwBytesRead, NULL) != FALSE)
    {
        // do something with lpBuffer here
    }

    delete [] lpBuffer;        
    
    CloseHandle(hFile);
}

Updating the resource data

Now it's simply a matter of getting access to the resource data of the test file and updating it with the data pointed to by lpBuffer. The third parameter to UpdateResource() is the name we want to give the resource. I just chose an arbitrary name of 104.

HANDLE hResource;

hResource = BeginUpdateResource(L"C:\\...\\t3.exe", FALSE);
if (NULL != hResource)
{
    if (UpdateResource(hResource, 
        RT_RCDATA, 
        MAKEINTRESOURCE(104), 
        MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), 
        (LPVOID) lpBuffer, 
        dwFileSize) != FALSE)
    {
        EndUpdateResource(hResource, FALSE);
    }
}

At this point, you can actually open the test file with Visual Studio and see the addition of our data in the "Data" section. Be sure to open the file as a "resource"!

Extracting the data

So now your application has been delivered, and you need to extract the resource data.

Extracting the resource data uses functions from the same family as UpdateResource(). The required steps are to load the file containing the resource data, find the desired resource, load the resource, and then lock it.

HMODULE hLibrary;
HRSRC hResource;
HGLOBAL hResourceLoaded;
LPBYTE lpBuffer;

hLibrary = LoadLibrary(L"C:\\...\\t3.exe");
if (NULL != hLibrary)
{
    hResource = FindResource(hLibrary, MAKEINTRESOURCE(104), RT_RCDATA);
    if (NULL != hResource)
    {
        hResourceLoaded = LoadResource(hLibrary, hResource);
        if (NULL != hResourceLoaded)        
        {
            lpBuffer = (LPBYTE) LockResource(hResourceLoaded);            
            if (NULL != lpBuffer)            
            {                
                // do something with lpBuffer here            
            }
        }    
    }

    FreeLibrary(hLibrary);
}

Saving the data to a file

All that's left is to create a file with the data pointed to by lpBuffer. Nothing special needs to be done to the data. It's the entire Windows calculator!

DWORD dwFileSize,
      dwBytesWritten;
HANDLE hFile;

dwFileSize = SizeofResource(hLibrary, hResource);

hFile = CreateFile(L"C:\\Winnt\\Temp\\calc2.exe",
                   GENERIC_WRITE,
                   0,
                   NULL,
                   CREATE_ALWAYS,
                   FILE_ATTRIBUTE_NORMAL,
                   NULL);

if (INVALID_HANDLE_VALUE != hFile)
{
    WriteFile(hFile, lpBuffer, dwFileSize, &dwBytesWritten, NULL);

    CloseHandle(hFile);
}

Now you should be able to run the newly created file, calc2.exe! As I indicated at the beginning of the article, this can be done with any sort of file that you want to include along with your main application or DLL.

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