CF_HDROP Explained: How Windows File Drop Lists Work

CF_HDROP is the standard format Windows uses to pass files through the clipboard and drag-and-drop. It holds a DROPFILES header followed by a double-null-terminated list of fully qualified paths, and no file data. File Explorer puts every selected item in one CF_HDROP; you read them with DragQueryFile, passing 0xFFFFFFFF first to get the count. When a tool shows only one of several copied files, it is usually reading the single-path CFSTR_FILENAME format instead of walking the whole list.

The layout

Microsoft describes CF_HDROP as the format "used when transferring the locations of a group of existing files". Unlike the other Shell formats, it is predefined, so you don't call RegisterClipboardFormat for it (its value is 15).

The data is a global memory object containing a DROPFILES structure:

After the header comes the list: each full path ends with a null character, and one extra null ends the list. For two files, Microsoft's example is:

c:\temp1.txt'\0'c:\temp2.txt'\0''\0'

Here '\0' stands for a single null character. The paths point at files on disk; if a file is deleted before the paste or drop, the entry still exists but the transfer fails.

Reading every path

Microsoft's documented procedure for a pasted or dropped file list:

1. Get the CF_HDROP data as an HGLOBAL and treat it as an HDROP.
2. Call DragQueryFile with iFile set to 0xFFFFFFFF. It returns the number of paths.
3. Call DragQueryFile once per index from 0 to count − 1. Passing a NULL buffer returns the length needed, not counting the terminating null.

A complete console program in C that lists whatever files are on the clipboard:

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

int main(void)
{
    if (!IsClipboardFormatAvailable(CF_HDROP)) {
        wprintf(L"No file list on the clipboard.\n");
        return 0;
    }
    if (!OpenClipboard(NULL)) {
        wprintf(L"Could not open the clipboard.\n");
        return 1;
    }

    HDROP hDrop = (HDROP)GetClipboardData(CF_HDROP);
    if (hDrop != NULL) {
        UINT count = DragQueryFileW(hDrop, 0xFFFFFFFF, NULL, 0);
        wprintf(L"%u item(s)\n", count);
        for (UINT i = 0; i < count; i++) {
            UINT len = DragQueryFileW(hDrop, i, NULL, 0);
            WCHAR *path = malloc((len + 1) * sizeof(WCHAR));
            if (path != NULL && DragQueryFileW(hDrop, i, path, len + 1) > 0) {
                wprintf(L"%ls\n", path);
            }
            free(path);
        }
    }

    CloseClipboard();
    return 0;
}

Build it with the Visual Studio developer prompt: cl listdrop.c user32.lib shell32.lib. Select several files in File Explorer, press Ctrl+C, and run it; every path should be listed.

Without a compiler, Windows PowerShell 5.1 does the same job:

Get-Clipboard -Format FileDropList

The -Format parameter exists only in Windows PowerShell 5.1; PowerShell 7's Get-Clipboard reads text only. In .NET, System.Windows.Forms.Clipboard.GetFileDropList() returns the list as a string collection. More clipboard commands are in the PowerShell clipboard cheat sheet.

The related Shell formats

An Explorer copy usually carries several formats besides CF_HDROP. The ones that matter most for bugs:

Why a tool sees only one of several files

Explorer itself puts the whole selection in one CF_HDROP; pasting into another Explorer folder proves it. When a clipboard manager or app shows only one file, look for these mistakes:

• Reading CFSTR_FILENAME. It holds one path by design. Its registered names are FileName (ANSI) and FileNameW (Unicode). Code that reads only that gets the first file and nothing else.
• Reading only the first index. Code that calls DragQueryFile with index 0 and never asks for the count.
• Parsing the list by hand with the wrong width. fWide says whether the paths are Unicode. Treating a wide list as ANSI, or the reverse, can stop the walk after the first entry. DragQueryFile handles this for you.
• Expecting CF_HDROP from virtual locations. Microsoft notes that data from virtual folders, which are usually not ordinary files, generally comes as CFSTR_FILEDESCRIPTOR/CFSTR_FILECONTENTS instead. Apps that accept files should handle both.

A three-file test catches all of these: create a.txt, b.txt and c.txt, copy all three in Explorer, paste them into a second folder as a control, then check what the tool recorded. If it can drag items back out, drag them into a third folder and count again.

Building a file list as a source

When your app puts files on the clipboard or starts a drag:

1. Offer CF_HDROP for every file that exists on disk. Microsoft's guidance is that existing files should be offered in this format.
2. Build the path list with a terminating null after each path and one more at the end, and set fWide for Unicode paths.
3. Add CFSTR_PREFERREDDROPEFFECT set to copy, unless the user chose Cut.
4. For an image that exists only in memory, write it to a file first and offer that file's path. A bitmap alone gives File Explorer nothing to drop.
5. For data that isn't a file, offer CFSTR_FILEDESCRIPTOR and CFSTR_FILECONTENTS rather than a path to a file that doesn't exist.

Be careful with moves. The Shell normally uses an optimized move, where the target moves the files itself and reports DROPEFFECT_NONE through CFSTR_PERFORMEDDROPEFFECT, meaning the source has nothing left to delete. A source that deletes on its own after every move can destroy data. Read CFSTR_LOGICALPERFORMEDDROPEFFECT if you need to know what the user saw happen.

Edge Drop, the clipboard shelf made by the team behind this site, follows the same model: it reads the full file list from an Explorer copy, stores the paths rather than the file data, and drags the original files back out through Electron's native drag. Images are written to a temporary PNG before the drag starts.

What this means for Win+V

Windows clipboard history stores text, HTML and bitmap images, so CF_HDROP never appears in it. A file copy lives only on the live clipboard until the next copy replaces it. How to copy multiple files and paste them somewhere else covers the everyday side, and what happens when you copy a folder shows how a folder fits in the same list. For why a drag can fail when paste works, see why paste works but drag-and-drop fails.

Related reading

• Why Paste Works but Drag-and-Drop Fails on Windows
• What Happens When You Copy a Folder to the Clipboard?
• How to Copy and Paste Multiple Files at Once in Windows
• PowerShell Clipboard Cheat Sheet: Get-Clipboard and Set-Clipboard

Sources

• Shell Clipboard Formats (Microsoft Learn) — CF_HDROP layout, CFSTR_FILENAME, SHELLIDLIST, FILEDESCRIPTOR/FILECONTENTS, drop-effect formats.
• Handling Shell Data Transfer Scenarios (Microsoft Learn) — reading paths with DragQueryFile, virtual folders, optimized moves.
• DROPFILES structure (Microsoft Learn) — pFiles, pt, fNC, fWide.
• DragQueryFileW function (Microsoft Learn) — 0xFFFFFFFF count and buffer sizing.
• Standard Clipboard Formats (Microsoft Learn) — CF_HDROP value 15.
• Get-Clipboard, Windows PowerShell 5.1 (Microsoft Learn) — -Format FileDropList.
• Clipboard.GetFileDropList (Microsoft Learn) — .NET file drop list.

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