# Autofix Multiple Def

> Fixes 'multiple definition' linker errors by removing duplicate symbols.

- Skill: `hyz0906/autofix-multiple-def` (Agent Skill)
- Install (CLI): `npx skillmds@latest add hyz0906/autofix-multiple-def`
- Raw SKILL.md: https://api.skillmd.com/api/skills/hyz0906/autofix-multiple-def/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: hyz0906 (https://skillmd.com/u/hyz0906)
- Updated: 2026-09-10
- Page: https://skillmd.com/skills/hyz0906/autofix-multiple-def

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# Multiple Definition Skill

Fixes linker errors where the same symbol is defined in multiple translation units.

## Detection Patterns
- `multiple definition of 'X'`
- `already defined in`
- `duplicate symbol`

## Strategy

1. **Identify Symbol**: Extract the duplicated symbol.
2. **Find Definitions**: Locate all places where it's defined.
3. **Remove Duplicates**: Keep one, remove or fix others.

## Instructions

### Step 1: Parse Error
From: `multiple definition of 'globalVar'; first defined in a.o`

### Step 2: Common Causes & Fixes

**Global variable in header:**
```cpp
// Wrong: header.h
int globalVar = 0;  // Defined in every .cpp that includes

// Fix Option 1: extern declaration
// header.h
extern int globalVar;
// source.cpp
int globalVar = 0;

// Fix Option 2: inline (C++17)
inline int globalVar = 0;
```

**Function defined in header:**
```cpp
// Wrong
void foo() { ... }  // in header

// Fix: make inline
inline void foo() { ... }
```

**Same source compiled twice:**
Check build file for duplicate source file entries.