C Through

See your C/C++ codebase, completely visible.

C Through brings Source Insight-style code intelligence into VS Code — built specifically for C and C++ developers who need more than what a standard editor provides.

Large C codebases are hard to navigate. Functions call other functions across dozens of files. Global variables get written in one place and read in five others. You spend more time chasing references than writing code. Source Insight solved this for decades with its Relational Window — but it's a separate, aging tool that lives outside your modern workflow.

C Through closes that gap. It runs entirely inside VS Code, requires zero configuration, no compiler, no build system — just open a file and your code structure appears instantly.

Current Version: 2.4.0

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Features

🌳 Sidebar Tree View

A live, structured breakdown of every C/C++ file — organized into collapsible sections:

• Includes — all #include dependencies with system vs local distinction
• Structs / Types — every struct and typedef with field listings
• Macros — function-like and value macros with their expansions
• Global Variables — file-scope variable declarations
• Functions — every function with its callers, callees, return type, and line number

Click any item to jump directly to its definition in the source file.

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🔍 Interactive Call Graph

A fully interactive visual graph of function call relationships.

• Pan — click and drag the canvas
• Zoom — scroll wheel or +/− buttons
• Click node — highlights it and fills the Selected Node card with its details
• Double-click node — collapse or expand that node's children independently
• Click +N badge — toggle a single node without affecting siblings
• ⬇ Top→Down / ➡ Left→Right — toggle layout direction
• Drill down — re-root the tree on any node
• ☰ Sidebar — collapsible Legend and Workspace Stats sections

Node colors:

Color	Meaning
🔵 Blue	Root function (current focus)
🟢 Green	Internal project function
🟠 Orange	External / unknown function
🔴 Red	Recursive call detected

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◇ Data Symbols in the Graph

The graph isn't limited to callers and callees. Toggle the ◇ toolbar button to see the globals, macros, and structs each function actually touches, drawn as diamond nodes attached to it.

Shape / Color	Meaning
◇ Orange	Global — written
◇ Blue	Global — read
◇ Purple	Global — address taken
◇ Cyan	Macro
◇ Pink	Struct / union

• Use the Globals / Macros / Structs checkboxes in the Legend to show only the kinds you care about
• Click any diamond to jump straight to that symbol's definition
• Selecting a function node lists every global, macro, and struct it uses in the Selected Node card — each one clickable — even with the ◇ nodes turned off

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💡 CodeLens Inline Metrics

Clickable annotations appear directly above every function definition — no panel switching required.

  ↑ 4 callers  ↓ 7 calls  🟡 complexity: 11  📄 main.c, driver.c
  int process_packet(PacketHeader *hdr, uint8_t *buf, int len) {

Lens	Click Action
↑ N callers	Open callers tree
↓ N calls	Open callees tree
🟢/🟡/🔴 complexity: N	Open relational tree
📄 file1.c, file2.c	Open callers tree (cross-file)
⊙ referenced N×	No direct callers — registered via pointer (hover for sites)
🌐 globals: g1, g2 · ✏️ 2 writes · 👁 3 reads	Globals this function touches
⚠ dead code — no callers found	Trigger workspace scan

Complexity thresholds:

• 🟢 1–9 — Simple, easy to test
• 🟡 10–19 — High, consider refactoring
• 🔴 20+ — Very high, hard to maintain

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📂 Flexible Scan Scope

Scope	How
Single file	Auto-analyzed on open
Specific directory	Right-click any folder → C Through: Analyze This Directory
Entire workspace	C Through: Analyze Entire Workspace
Re-scan	Re-scan Last Scope button in sidebar toolbar

Cross-file caller/callee relationships are fully resolved after any multi-file scan.

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🔍 Search & Filter

Sidebar Search & Filter: The C Through: Search & Filter panel sits above the sidebar tree with an embedded search box and category checkboxes.

• Type any part of a name in the search box — Includes, Structs, Macros, Globals, and Functions filter to matches instantly (no pop-up)
• Toggle the Includes / Structs / Macros / Globals / Functions checkboxes to show or hide whole sections, with Select all / Clear all shortcuts
• Click ✕ to clear the search
• The 🔍 toolbar icon (or Ctrl+Shift+P → C Through: Search Sidebar) reveals and focuses the search box
• Press Ctrl+Alt+S (Cmd+Alt+S on macOS) to jump straight into the search box from anywhere — rebind it via the ⌨ Shortcut link in the panel or C Through: Configure Keyboard Shortcuts

Call Graph Search: Search inside the visual call graph to find nodes quickly.

• Type in the Search nodes… input box in the call graph toolbar
• Matching nodes are highlighted at full opacity with a glow effect
• Non-matching nodes are dimmed to 20% opacity
• Click ✕ to clear the search
• Search term persists across panel re-opens

Cursor Sync: Keep the sidebar in step with where you are in the code.

• Move the editor cursor to a function or global variable — the C Through tree selects and reveals that symbol
• Placing the cursor on a call site reveals the called function's definition; elsewhere it selects the enclosing function
• Highlights without stealing focus from the editor
• Toggle off with the cThrough.syncCursor setting

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☠ Dead Code Report

A dedicated report panel showing all dead and unused code across your entire workspace.

Open via Ctrl+Shift+P → C Through: Show Dead Code Report or the ⚠ button in the sidebar toolbar.

Detects:

• Unused Functions — no callers and no indirect references, with severity and confidence rating. Functions registered in command tables or used as thread entries / callbacks are recognised as live and not reported
• Unused Globals — declared but never referenced, or written but never read
• Unused Macros — defined but never referenced in any function body
• Unresolved Externs — extern declarations with no definition found in scanned files

Panel features:

• Summary dashboard with counts by category and severity
• Tabs: All / Functions / Globals / Macros / Unresolved Externs
• Filter bar to search findings by name or file
• Click any row to jump directly to that source line
• ⟳ Analyze Workspace button to re-scan and refresh the report
• Dark / Light theme toggle

Severity levels:

Level	Meaning
🔴 High	Static function with no callers, or global never referenced
🟡 Medium	Non-static function with no callers, or write-only global
🟢 Low	Unused macro
⚪ Info	Unresolved extern declaration

Note: Always run Analyze Entire Workspace before opening the report for accurate cross-file results.

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🔗 Indirect References — Commands, Threads & Callbacks

Not every function is called directly. In embedded and CLI codebases, functions are registered in command tables, handed to task-creation APIs, or wired up as callbacks — so a naive "who calls this?" says nobody.

C Through finds those registration sites:

static struct cmds show_subcmds[] = {
    { "config-list", MATCH_AMB, 0, 0, do_show_config_list, NULL, ... },  // ← found
};
tid = thread_create("ipacl", PRI_NORMAL, 0, 1024*64, ip_acl, NULL, 0);      // ← found

• Functions referenced by pointer show a Referenced (N) section listing every registration site
• CodeLens shows ⊙ referenced N× instead of 💀 0 callers
• They are excluded from the Dead Code Report — no more false "unused function" noise
• Scope-aware: a parameter or local named like a function (int vty) is not mistaken for a reference

These are references, not resolved call edges — C Through shows you where a function is registered, and treats it as live. It does not draw a fake call arrow from the dispatcher.

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⚡ Auto-Refresh on Save

Save a file and only that file is re-parsed — the sidebar, CodeLens, and indexes update in place, with no full workspace rescan.

• Enabled by default; turn off with cThrough.autoRefresh
• Only files inside your last scan scope are refreshed
• A 4,700-line file re-parses in roughly 75 ms

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🔎 Global Variable Reference Tracker

Expand any global variable in the sidebar to see its complete usage across all files:

• Defined / Extern declared — where it lives and where it is imported
• Written — every function that assigns to it, with file and line
• Read — every function that reads it (conditions, expressions, right-hand values)
• Address taken — every &var usage

Writes are detected beyond plain = assignment:

Pattern	Counted as
g = x; · g += x; · g++	write
arr[i] = x; · s[6].field = x; · p->next->val = x;	write to the base global
strcpy(g, s) · memcpy(g, …) · sprintf(g, …) · memset(&g, …)	write (destination argument)
if (g == 1) · y = g + 1; · f(g)	read

Every entry is clickable and jumps to the exact source line.

CodeLens above every global declaration shows:

    🌐 global  int    ✏️ 3 writes  👁 7 reads  · 4 functions  · 2 files
    int g_counter = 0;

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Installation

From VS Code Marketplace

1. Press Ctrl+Shift+X
2. Search "C Through"
3. Click Install

From VSIX

code --install-extension c-through-2.4.0.vsix

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Usage

Quick Start

1. Open any .c or .h file — auto-analyzed, C Through panel appears in Explorer sidebar
2. Place cursor on any function name → right-click → C Through: Show Relational Tree

Commands (Ctrl+Shift+P)

Command	Description
C Through: Analyze Current File	Parse the active C/C++ file
C Through: Analyze Entire Workspace	Scan all C/C++ files in workspace
C Through: Analyze This Directory	Pick a folder to scan
C Through: Re-scan Last Scope	Repeat the previous scan
C Through: Show Relational Tree	Open call graph for symbol at cursor
C Through: Show Functions Called By This	Open callees tree
C Through: Show Functions Calling This	Open callers tree
C Through: Toggle CodeLens	Show/hide inline CodeLens
C Through: Search Sidebar	Reveal & focus the Search & Filter box (Ctrl+Alt+S)
C Through: Configure Keyboard Shortcuts	Open Keyboard Shortcuts filtered to C Through commands
C Through: Show Dead Code Report	Open the dead code analysis report panel

Context Menus

• Editor — right-click inside any C/C++ file for tree commands
• Explorer — right-click any folder for Analyze This Directory

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Settings

Setting	Default	Description
cThrough.maxDepth	5	Maximum call tree traversal depth
cThrough.showStdLib	false	Include stdlib calls in tree
cThrough.autoRefresh	true	Re-parse file on save
cThrough.enableCodeLens	true	Show inline CodeLens
cThrough.syncCursor	true	Select the symbol at the editor cursor in the sidebar
cThrough.includeGlob	**/*.{c,h,cpp,hpp}	File pattern for scan
cThrough.excludeGlob	**/node_modules/**	Paths to exclude from scan

Example — scan only src/, skip build/ and vendor/:

{
  "cThrough.includeGlob": "src/**/*.{c,h}",
  "cThrough.excludeGlob": "{**/build/**,**/vendor/**,**/third_party/**}"
}

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How It Works

C Through uses regex-based static analysis — no compiler, no language server, no build system required. It indexes code that would otherwise need a working compile_commands.json, which makes it useful on vendor SDKs and embedded trees that never build cleanly inside an IDE.

The parser:

1. Strips comments and string/char literal contents (line positions preserved)
2. Extracts #include, #define, struct/typedef definitions
3. Identifies function definitions by signature pattern matching
4. Extracts all call sites inside each function body
5. Classifies global variable access per function — read / write / address-taken
6. Collects macro and struct/type usage per function
7. Finds indirect references (function names used as values, not calls)
8. Calculates cyclomatic complexity per function
9. Builds a cross-file caller/callee index across all scanned files

Speed — measured on a real embedded C tree (81 files, 28.5k lines):

Operation	Time
Analyze workspace (28.5k lines)	~430 ms
Analyze workspace (286k lines)	~3.5 s
Sidebar load	~2 ms
Call graph (2,000 nodes)	~9 ms
Re-parse on save (4,700-line file)	~75 ms

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Known Limitations

C Through trades compiler-grade accuracy for zero setup and speed. Where that shows:

• No preprocessor evaluation — code inside #if / #ifdef branches is parsed regardless of whether it would actually compile
• Function-pointer call targets are not resolved — fp() is recorded as a call to fp, not to whatever it points at. (Where a function is registered — command tables, thread entries, callbacks — is detected; see Indirect References)
• Macro-generated signatures are not expanded — when a macro builds the whole declaration (DEFINE_HANDLER(alpha) { … }), the real function name is never seen, and the macro name can surface as a symbol instead. Macro-prefixed signatures (PAM_EXTERN int f(), ULONG f(), BOOL f()) parse correctly
• Macro and struct usage links to the definition, not to each use site — they are matched by name against the macro/struct tables, so there is no per-use line number
• C++ support is minimal — the parser targets C. Templates and class member functions are not indexed; .cpp/.hpp files are scanned for C-style constructs only
• Analysis is in-memory — there is no on-disk symbol database, so a workspace scan is repeated after a VS Code restart

For compiler-accurate go-to-definition and find-all-references, pair C Through with clangd or C/C++ IntelliSense — C Through is for seeing the shape of the code, especially where those tools cannot be configured.

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License

MIT © 2026