The left and right File panes show the text contents and differences of the two files being compared. The File panes are the main area for navigating and merging differences, and also allow you to edit the text directly. This section describes the features that support these actions, and ways that you can customize the File panes.

2.1.6. File pane margins

The File panes have optional gray margins that show line numbers and some symbols. To show or hide the margins, clicking View → View Margins. If you are using multiple File Compare windows, you can control margins for each window independently. The margin can show any or all of these features:

• Line numbers, if View → View Line Numbers is enabled.

• Bookmarks, if Edit → Bookmarks is enabled. A bookmark is a blue circle, in the margin next to a line, that you can make WinMerge remember and return to.

  • To set a bookmark on a line, double-click in its margin (or press Ctrl+F2). The same action deletes an existing bookmark.

  • To navigate bookmarks, click Edit → Bookmarks and choose Next or Previous.

  • Double-click a single bookmark to delete it (or press Ctrl+F2).

  • Click Edit → Bookmarks → Clear All Bookmarks to delete all bookmarks.

• Word wrap arrow symbols, if View → Wrap Lines is enabled.

The following screenshot shows a margin with bookmarks and word wrap enabled. Without line numbers, the margin width is minimal.

The next screenshot shows a margin with bookmarks and line numbers enabled. Notice that the margin is wider. In fact, the margin is wide enough for the largest line number. Thus, the margins for large files with many lines can be quite wide.

The WinMerge toolbar and menus provide a range of functions to navigate, select, and merge differences within files.

The difference functions you can use depend on your context, which often changes as you work. This means that a function is available only when its operation is possible for a given location or other condition in your WinMerge environment. For example, if you click in a line of text within a difference, you might notice several navigation and merge buttons become enabled in the toolbar. If you click in another area of text that is not within a difference, these functions become unavailable.

Difference functions are available in the WinMerge toolbar,and also through these alternate mechanisms:

Difference functions are described in Navigating differences and Merging differences, later in this topic. Quick start and Overview of file comparing and merging provide examples of comparing and merging.

When you compare three text files and specify a merge output path (for example, when a version control tool starts WinMerge with the /o command-line option), the Merge Result pane opens at the bottom of the File Compare window. It works like the merge output window in KDiff3: the three File panes show the compared files read-only, and the Merge Result pane contains the merge result, which you can edit freely. This requires the Merge Result pane option to be enabled in the Compare/Merge page of the Options dialog.

When you open a two-way conflict file with File → Open Conflict File, WinMerge keeps the two source panes side by side and opens the Merge Result pane when it is enabled. Each differing block starts unresolved because a two-way conflict file has no common base. Choose the left or right source to resolve a block. In this mode the toolbar buttons are numbered 1 and 2, and Ctrl+Shift+1 and Ctrl+Shift+2 choose the left and right source, respectively. Unresolved blocks are saved using the standard two-sided conflict markers.

When the pane opens, every difference initially starts unresolved, shown as a compact <Merge Conflict> or <Unresolved Difference> placeholder line. If an automatic merge is requested — with the /al, /am or /ar command-line option, or with the Auto Merge command — non-conflicting differences are resolved automatically according to the selected merge target, and only true conflicts, where both sides changed the same lines relative to the base, remain unresolved.

To resolve a difference, select it and choose the desired source from the top-level Merge Result menu. Two-way merge sessions offer Choose Left and Choose Right; three-way sessions also offer Choose Middle. You can also use the Merge Result pane context menu, or the 1 / 2 / 3 toolbar buttons. Each command toggles that pane's lines for the current difference (or all differences covered by the current selection): selecting several panes combines their lines in the order you select them (useful when both sides added something and the merge should keep both), and deselecting all panes makes the difference unresolved again. You can also type corrections directly into the Merge Result pane, except on unresolved differences: those must be resolved with a Choose command before their text can be edited. Conflicts whose sides differ only in white space are marked as (Whitespace only).

The pane's margin shows where every line came from: 1, 2 or 3 for a line taken from the left, middle or right pane (matching the toolbar buttons), ? for an unresolved conflict section, and m for a difference modified by hand. The pane's status bar shows how many differences are still unresolved. While the pane is open, Next Conflict and Previous Conflict (Alt+Shift+Down / Alt+Shift+Up) jump to the next or previous difference that still needs a decision, skipping the ones already resolved.

Use File → Save → Save Merge Result, the Save toolbar button, or Ctrl+S to save the result to the output path. WinMerge warns if unresolved differences remain. Unresolved conflicts are saved as standard conflict sections — never as placeholder text — so the file keeps all versions of the disputed lines and can be finished later in any editor or merge tool; unresolved non-conflicting differences are saved with their automatic merge content, keeping the output free of conflict markers that no version control system would produce. Reopening the output path itself does not resume from these conflict sections: WinMerge always rebuilds the merge result from the three compared files, so a version control tool that starts WinMerge again with the /o command-line option (for example git mergetool) gets a fresh merge every time, regardless of what the output file already contains. To pick up an earlier, partially resolved conflict file instead, use File → Open Conflict File : WinMerge parses its conflict sections and restores them as unresolved differences, keeping any text that was already resolved. WinMerge also prompts about an unsaved merge result when the window is closed — also when the pane itself has been hidden in the meantime. By default every line is saved with its own original line ending, so the output differs from the sources as little as possible (for example, producing minimal diffs in version control); you can change the output line endings to Windows, Unix, or classic Mac style from the Merge Result pane's status bar. The encoding follows the side that changed it, and the save honors the backup-file option and any file packer plugin the files were opened with.

You can also start a merge in any three-way text comparison with Merge → Start Merge Session (differences start unresolved) or Merge → Auto Merge (non-conflicting differences are resolved automatically). While a merge session is active, you can show and hide the pane with View → Merge Result Pane . To end the merge session and restore the normal editable three-pane behavior, choose Merge → End Merge Session. WinMerge prompts to save if the merge result has unsaved changes, and restores the panes' original read-only states and headers.

The Location pane, to the left of the File panes, maps the entire length of the compared files into two vertical bars (corresponding to the left and right File panes). It is especially useful for working with files that are too long to easily navigate in the File panes.

The Location pane shows several kinds of items:

The Location pane's context menu contains these shortcuts:

The Diff pane shows the contents of the two sides of a selected difference.

When you select a difference, the two versions are loaded in the upper and lower sides of the Diff pane. In this way, the Diff pane confirms which lines are included in a difference, and lets you examine them in isolation from the rest of the file.

You can merge differences directly in the Diff pane by right-clicking in either the top or bottom side and choosing Copy to Right or Copy to Left.

Each File pane contains a status bar at the bottom. The status bar contains several panes with different types of information about the document and your location in it:

When a File Compare window is open, the WinMerge window status bar shows one of these messages about the compared files:

Here are the functions for navigating differences in the File Compare window, and their shortcuts in the toolbar and menus:

By default, the Automatic rescan option is enabled in the Editor page of WinMerge options. Rescanning keeps your compare and merge operations up to date. Without rescanning, WinMerge differences does not detect changes that might occur to files while you are comparing them, for example in an external editor.

Rescanning occurs when you perform certain actions (like merging a difference or editing a file) during a file compare. If a file has changed, WinMerge displays a dialog advising you that another application has updated the file, and asks whether you want to reload the file.

Click Yes to reload the file before proceeding, or No to ignore the changes and work with the earlier loaded version of the file.

The merging functions can implicitly select differences based on a cursor location or text selection. For example, if you click anywhere in a difference and then click the Copy Right toolbar button, the entire difference block is merged. This makes it easy to merge many small differences. Similarly, if you select text that spans all or part of multiple differences, all the included differences are merged with a single merge command.

If the result of a merge operation is not what you expected, you can click Undo to reverse the operation.

Here are the merge functions and their shortcuts in the toolbar and menus:

You can use WinMerge to resolve conflict files that some version control systems produce during their merge operations. A conflict file is created when a merge encounters differences that cannot be automatically resolved. It is a single file containing the incompletely merged content of the two files. WinMerge separates the conflict file into separate files and opens those files in file Compare window. You can then use WinMerge's compare and merge functions to resolve the conflicts and save the merged result file.

Many version control systems allow you to configure an external merge tool. If yours does, you might be able to have your version control system launch WinMerge automatically when a merge conflict occurs.

You can also open a conflict file from the WinMerge command line, which accepts three filename parameters: Theirs, Mine, and optionally, Resolved (if you want a different result file from the conflict file). For more information, see Command line. Single path to the conflict file is also accepted in command line.