- 1 year ago
Memory mapped file truncation on windows
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On Windows, memory-mapped files can be truncated using the SetFilePointer
and SetEndOfFile
functions. Memory-mapped files provide a way to map a section of a file directly into memory, allowing efficient random access and sharing of data between processes.
Here's a step-by-step guide on how to truncate a memory-mapped file in Windows:
- Open the File:
First, you need to open the file with the appropriate access rights. Use theCreateFile
function to open the file.
cpp#include <Windows.h>
HANDLE hFile = CreateFile(
L"C:\\path\\to\\file.txt", // Replace with the path to your file
GENERIC_READ | GENERIC_WRITE, // Access rights: read and write
FILE_SHARE_READ, // Share mode: allow other processes to read the file
NULL, // Security attributes
OPEN_EXISTING, // Open existing file
FILE_ATTRIBUTE_NORMAL, // File attributes
NULL // Template file
);
if (hFile == INVALID_HANDLE_VALUE) {
// Handle error
return 1;
}
- Get the File Size:
Use theGetFileSize
function to obtain the current size of the file.
cppDWORD fileSize = GetFileSize(hFile, NULL);
if (fileSize == INVALID_FILE_SIZE) {
// Handle error
CloseHandle(hFile);
return 1;
}
- Set the File Pointer:
Use theSetFilePointer
function to set the file pointer to the desired new size.
cppDWORD newFileSize = 1024; // Replace with the new desired file size
if (SetFilePointer(hFile, newFileSize, NULL, FILE_BEGIN) == INVALID_SET_FILE_POINTER) {
// Handle error
CloseHandle(hFile);
return 1;
}
- Truncate the File:
Use theSetEndOfFile
function to truncate the file to the new size.
cppif (!SetEndOfFile(hFile)) {
// Handle error
CloseHandle(hFile);
return 1;
}
- Close the File Handle:
Close the file handle when you're done with the file.
cppCloseHandle(hFile);
After following these steps, the memory-mapped file will be truncated to the new desired size. Please note that truncating a file using the methods above will result in data loss if the new file size is smaller than the original file size. Make sure to handle data truncation carefully and back up any important data before proceeding with the file truncation.