Advanced Diff Checking Techniques for Code Reviews: Complete Guide

Unified Diff Format:

--- file1.txt
+++ file2.txt
@@ -1,3 +1,4 @@
 unchanged line
-removed line
+added line
+another new line
 unchanged line

Reading the Symbols:

• - — Line was removed
• + — Line was added
• No prefix — Line unchanged (context)
• @@ — Chunk header showing line ranges

Split View vs Unified:

• Unified: Shows changes inline (good for small changes)
• Split: Side-by-side (better for large refactors)

Essential Git Diff Commands:

# See unstaged changes
git diff

# See staged changes
git diff --staged

# Compare branches
git diff main..feature-branch

# Compare specific files
git diff HEAD~1 file.js

# Word-level diff (better for prose)
git diff --word-diff

# Ignore whitespace changes
git diff -w

Advanced Options:

• --stat — Summary of changes
• --name-only — List changed files only
• --patience — Better algorithm for moved code

Use Online Tools When:

• Comparing config files outside version control
• Debugging JSON/XML responses
• Reviewing non-code text changes
• Quick ad-hoc comparisons
• Sharing diff with non-technical stakeholders

Use Git Diff When:

• Code is in version control
• Reviewing pull requests
• Comparing commit history
• Merge conflict resolution

Try our Diff Checker for quick comparisons.

Myers Algorithm (Default):

Fast and works well for most cases. Minimizes number of edits.

Patience Algorithm:

Better for code that has been reorganized. Produces more intuitive diffs when code blocks are moved.

git diff --patience

Histogram Algorithm:

Like patience but faster. Good default for large files.

git diff --histogram

When to Switch: If git diff shows confusing changes for moved code, try --patience or --histogram.

Understanding Conflict Markers:

<<<<<<< HEAD
Your current changes
=======
Incoming changes
>>>>>>> feature-branch

Resolution Strategy:

1. Use git diff to see what changed in both branches
2. Identify the actual conflict (logic vs formatting)
3. Manually merge, keeping necessary parts from both
4. Remove conflict markers
5. Test thoroughly
6. Commit the resolution

Tools: VSCode, GitKraken, KDiff3, Meld provide visual merge diff tools.

Effective Diff-Based Code Review:

1. Start with high-level: git diff --stat for overview
2. Review file-by-file: Don't try to review 50 files at once
3. Ignore formatting: Use git diff -w to ignore whitespace
4. Focus on logic: Look for edge cases, null checks, performance
5. Ask questions: Comment on unclear changes
6. Approve incrementally: Break large PRs into smaller ones

Red Flags in Diffs:

• Large functions added without tests
• Security-sensitive code (auth, validation)
• Database schema changes
• Commented-out code
• TODO/FIXME comments