MapViewOfFile chunked loading of file - winapi

Question

I want to map file into memory with chunk size equal system granularity. First chunk read without error and all others fails with error 5 (ERROR_ACCESS_DENIED). I tried run program with administrator privileges.
My code:
#include <windows.h>
#include <stdio.h>
int main() {
HANDLE hFile = CreateFile( TEXT("db.txt"),
GENERIC_READ,
FILE_SHARE_READ,
NULL,
OPEN_EXISTING,
FILE_ATTRIBUTE_NORMAL,
NULL);
if (hFile == INVALID_HANDLE_VALUE) {
printf("[ERROR] File opening error %d\n", GetLastError());
return 1;
}
printf("[DONE] File opened successfully.\n");
HANDLE hMap = CreateFileMapping(hFile, NULL, PAGE_READONLY, 0, 0, NULL);
if (hMap == NULL) {
printf("[ERROR] Create mapping error %d\n", GetLastError());
return 2;
}
printf("[DONE] Create mapping successfully.\n");
LARGE_INTEGER file_size = { };
if (!GetFileSizeEx(hFile, &file_size)) {
printf("[ERROR] Getiing filesize error %d\n", GetLastError());
return 3;
}
printf("[DONE] Getting file size.\n");
SYSTEM_INFO info = { };
GetSystemInfo(&info);
printf("[DONE] Getting system memory granularity %d.\n", info.dwAllocationGranularity);
DWORD offset = 0;
int size = 0;
do {
char* ENTRY = (char*)MapViewOfFile(hMap, FILE_MAP_READ, HIWORD(offset), LOWORD(offset), info.dwAllocationGranularity);
if (ENTRY == NULL) {
printf("[ERROR] Map entry error %d\n", GetLastError());
} else {
printf("[DONE] MAPPING PART WITH OFFSET %d\n", offset);
//printf("%s\n", ENTRY);
}
if (offset + info.dwAllocationGranularity < file_size.QuadPart) {
offset += info.dwAllocationGranularity;
} else {
offset = file_size.QuadPart;
}
//offset += size;
UnmapViewOfFile(ENTRY);
} while (offset < file_size.QuadPart);
CloseHandle(hMap);
CloseHandle(hFile);
system("pause");
return 0;
}
How I fix it?

Answer 1

You're using HIWORD and LOWORD for the offset in the call to MapViewOfFile, but these only take a 32-bit value and split it into two 16-bit halves - what you want is a 64-bit value split into two 32-bit halves.
Instead you need HIDWORD and LODWORD, which are defined in <intsafe.h>:
#define LODWORD(_qw) ((DWORD)(_qw))
#define HIDWORD(_qw) ((DWORD)(((_qw) >> 32) & 0xffffffff))
Like so:
char* ENTRY = (char*)MapViewOfFile(hMap, FILE_MAP_READ, HIDWORD(offset), LODWORD(offset), info.dwAllocationGranularity);
You need this even though your offset variable is 32 bit (in which case, HIDWORD will just return 0 and the full value of offset is passed as the low-order DWORD).