inter-file-deps

Inter-File Dependencies Example

Demonstrates hot reloading functions that call other functions across multiple files.

The Setup

Three files work together:

• utils.cpp - Helper functions (getMultiplier(), getAdder())
• calculator.cpp - The file we'll hot reload (calls functions from utils.cpp)
• main.cpp - Main program loop

The Bug

calculator.cpp line 8 should multiply by 20, but only multiplies by 10.

// Current (wrong):
return x * getMultiplier();  // getMultiplier() returns 10, so 5 * 10 = 50

// Fix:
return x * getMultiplier() * 2;  // 5 * 10 * 2 = 100 ✓

Quick Start

# Build (note the -rdynamic flag!)
./build.sh

# Debug
lldb ./myapp
(lldb) command script import ../../src/hotreload.py
(lldb) b main.cpp:27
(lldb) run

The program will print:

calculate(5) = 50 (expected: 100)
Fix the bug and run: (lldb) hotreload calculator.cpp

Fix the Bug

Edit calculator.cpp line 8:

return x * getMultiplier() * 2;  // Add the * 2

Save the file.

Hot Reload

(lldb) hotreload calculator.cpp
(lldb) continue

You should see:

✓ Patched 2/2 functions
calculate(5) = 100 (expected: 100)
SUCCESS! Hot reload worked!

What This Demonstrates

• ✅ Inter-file dependencies - calculator.cpp calls getMultiplier() from utils.cpp
• ✅ Runtime symbol resolution - Uses RTLD_GLOBAL + -rdynamic
• ✅ Multiple functions - Hot reloads both calculate() and complexCalculation()

Key Requirement: -rdynamic

This example requires the binary to be built with -rdynamic:

clang++ -rdynamic -g -O0 main.cpp utils.cpp calculator.cpp -o myapp

Why? The -rdynamic flag exports symbols to the dynamic symbol table so the hot-reloaded .so can find functions from the original binary at runtime.

Without it, you'll see:

✗ dlopen() failed: undefined symbol: _Z13getMultiplierv

⚠ HINT: Your binary may not have been built with -rdynamic

Files

• main.cpp - Main program
• calculator.cpp - Hot reload this file
• utils.cpp - Helper functions
• utils.h - Header file
• build.sh - Build script (includes -rdynamic)
• compile_commands.json - Compiler flags