SetFilePointer

Namespace: FileAPI

Header: Windows.h

Library: Kernel32.lib

DLL: Kernel32.dll

Synopsis

DWORD WINAPI SetFilePointer(
    HANDLE hFile,
    LONG   lDistanceToMove,
    PLONG  lpDistanceToMoveHigh,
    DWORD  dwMoveMethod
);

Parameters

hFile – A handle to the file. The handle must have been created with GENERIC_READ or GENERIC_WRITE.
lDistanceToMove – The low-order 32 bits of the distance to move the file pointer.
lpDistanceToMoveHigh – Pointer to the high-order 32 bits of the distance to move. Set to NULL if not needed.
dwMoveMethod – Starting point for the move. One of:
- FILE_BEGIN – Beginning of the file.
- FILE_CURRENT – Current file pointer.
- FILE_END – End of the file.

Return Value

If the function succeeds, the return value is the low-order DWORD of the new file pointer. On failure, the return value is INVALID_SET_FILE_POINTER (0xFFFFFFFF) and you can call GetLastError for extended error information.

Remarks

SetFilePointer moves the file pointer associated with a file handle. It can be used to seek forward or backward in a file, or to obtain the current file pointer position by passing a zero distance and FILE_CURRENT.

Example

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

int main(void)
{
    HANDLE hFile = CreateFileA(
        "example.bin",
        GENERIC_READ | GENERIC_WRITE,
        0,
        NULL,
        OPEN_ALWAYS,
        FILE_ATTRIBUTE_NORMAL,
        NULL);

    if (hFile == INVALID_HANDLE_VALUE) {
        printf("CreateFile failed (error %lu)\\n", GetLastError());
        return 1;
    }

    // Move to the end of the file
    LONG high = 0;
    DWORD pos = SetFilePointer(hFile, 0, &high, FILE_END);
    if (pos == INVALID_SET_FILE_POINTER && GetLastError() != NO_ERROR) {
        printf("SetFilePointer failed (error %lu)\\n", GetLastError());
        CloseHandle(hFile);
        return 1;
    }

    printf("Current file size: %llu bytes\\n",
           ((unsigned long long)high << 32) | pos);

    // Write some data at the end
    const char *text = "Hello, SetFilePointer!\\n";
    DWORD written;
    WriteFile(hFile, text, (DWORD)strlen(text), &written, NULL);

    printf("Wrote %lu bytes.\\n", written);

    CloseHandle(hFile);
    return 0;
}

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