program.c

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

#define MB (1024 * 1024)

int main() {
    HANDLE hFile, hFile2;
    DWORD bytesWritten;
    LARGE_INTEGER fileSize, moveAmount;
    char* buffer = malloc(MB);
    
    int i;

	DeleteFileA("R:\\original_file.bin");
	DeleteFileA("R:\\another_file.bin");

    hFile = CreateFileA("R:/original_file.bin", GENERIC_READ | GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
    if (hFile == INVALID_HANDLE_VALUE) {
        printf("Error creating file: %d\n", GetLastError());
        exit(__LINE__);
    }

    for (int i = 0; i < 20; i++) {
        if (!WriteFile(hFile, buffer, MB, &bytesWritten, NULL)) {
            fprintf(stderr, "WriteFile failed on iteration %d: %x\n", i, GetLastError());
            exit(__LINE__);
        }
    }

    if (!FlushFileBuffers(hFile)) {
        fprintf(stderr, "Could not flush file buffers: %x\n", GetLastError());
        exit(__LINE__);
    }


    FILE_ZERO_DATA_INFORMATION zeroDataInfo;
    zeroDataInfo.FileOffset.QuadPart = 6 * MB; 
    zeroDataInfo.BeyondFinalZero.QuadPart = 18 * MB; 

    if (!DeviceIoControl(hFile, FSCTL_SET_SPARSE, NULL, 0, NULL, 0, NULL, NULL) || 
        !DeviceIoControl(hFile, FSCTL_SET_ZERO_DATA, &zeroDataInfo, sizeof(zeroDataInfo), NULL, 0, NULL, NULL)) {
		printf("Error setting zero data: %d\n", GetLastError());
        exit(__LINE__);
	}

    if (!FlushFileBuffers(hFile)) {
        fprintf(stderr, "Could not flush file buffers: %x\n", GetLastError());
        exit(__LINE__);
    }


    // Create another file of size 4 MB
    hFile2 = CreateFileA("R:/another_file.bin", GENERIC_READ | GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
    if (hFile2 == INVALID_HANDLE_VALUE) {
        printf("Error creating second file: %d\n", GetLastError());
        exit(__LINE__);
    }


    for (int i = 0; i < 12; i++) {
        if (!WriteFile(hFile2, buffer, MB, &bytesWritten, NULL)) {
            fprintf(stderr, "WriteFile 2 failed on iteration %d: %x\n", i, GetLastError());
            exit(__LINE__);
        }
        if (bytesWritten != MB) {
            fprintf(stderr, "Failed to write full buffer 2 on iteration %d\n", i);
            exit(__LINE__);
        }
    } 
    
    
    HANDLE hMapFile = CreateFileMapping(hFile, NULL, PAGE_READWRITE, 0, 0, NULL);
    if (hMapFile == NULL) {
        fprintf(stderr, "Could not create file mapping object: %x\n", GetLastError());
        exit(__LINE__);

    }

    char* lpMapAddress = MapViewOfFile(hMapFile, FILE_MAP_WRITE, 0, 0, 0);
    if (lpMapAddress == NULL) {
        fprintf(stderr, "Could not map view of file: %x\n", GetLastError());
        exit(__LINE__);
    }

	moveAmount.QuadPart = 6 * MB;
	SetFilePointerEx(hFile, moveAmount, NULL, FILE_BEGIN);

    for (i = 6 ; i < 10 ; i++) {
        if (!WriteFile(hFile, buffer, MB, &bytesWritten, NULL)) {
            fprintf(stderr, "WriteFile failed on iteration %d: %x\n", i, GetLastError());
            exit(__LINE__);
        }
    }

    if (!FlushViewOfFile(lpMapAddress, 0)) {
        fprintf(stderr, "Could not flush view of file: %x\n", GetLastError());
        exit(__LINE__);
    }

    if (!FlushFileBuffers(hFile)) {
	    fprintf(stderr, "Could not flush file buffers: %x\n", GetLastError());
        exit(__LINE__);
    }

    return 0;
}