- 1 year ago
SEEK_FAILURE What to do if SetFilePointer fails if file is over 4.1 GB
If the SetFilePointer
function fails when attempting to seek within a file larger than 4.1 GB on Windows, it is likely due to the limitation of the 32-bit LONG
data type used by SetFilePointer
. To overcome this limitation and work with files larger than 4.1 GB, you can use the SetFilePointerEx
function, which supports 64-bit file offsets.
Here's an example of how to use SetFilePointerEx
to perform seeking within a large file:
cpp#include <iostream>
#include <Windows.h>
int main() {
HANDLE hFile = CreateFile(
L"large_file.txt", // Replace with your file path
GENERIC_READ, // Desired access mode
0, // Share mode (no sharing)
nullptr, // Security attributes (default)
OPEN_EXISTING, // Open existing file
FILE_ATTRIBUTE_NORMAL, // File attributes (default)
nullptr // Template file (none)
);
if (hFile != INVALID_HANDLE_VALUE) {
LARGE_INTEGER distanceToMove;
distanceToMove.QuadPart = 1234567890; // Replace with the desired file offset
LARGE_INTEGER newFilePointer;
if (SetFilePointerEx(hFile, distanceToMove, &newFilePointer, FILE_BEGIN)) {
// Seek operation succeeded
std::cout << "New file pointer: " << newFilePointer.QuadPart << std::endl;
}
else {
// Seek operation failed
DWORD error = GetLastError();
std::cout << "Seek operation failed with error code: " << error << std::endl;
}
CloseHandle(hFile);
}
else {
// Failed to open the file
DWORD error = GetLastError();
std::cout << "Failed to open the file with error code: " << error << std::endl;
}
return 0;
}
In this example, the SetFilePointerEx
function is used to seek within a file larger than 4.1 GB. The distanceToMove
variable is a LARGE_INTEGER
structure representing the desired file offset. Replace the 1234567890
value with the desired offset in bytes. The newFilePointer
variable is a LARGE_INTEGER
structure that receives the new file pointer position.
If SetFilePointerEx
succeeds, it returns a non-zero value, and the new file pointer position can be retrieved from the newFilePointer
variable. If SetFilePointerEx
fails, it returns zero, and you can use GetLastError
to obtain the error code for further analysis.
By using SetFilePointerEx
instead of SetFilePointer
, you can overcome the limitations related to 32-bit file offsets and work with files larger than 4.1 GB on Windows.