Modules

C++20 Modules

C++20 introduced modules as a modern replacement for header files.

Problems with Headers

┌─────────────────────────────────────────────────────────────┐
│              Headers vs Modules                               │
├─────────────────────────────────────────────────────────────┤
│                                                             │
│  Headers (.h)           |  Modules (.cppm)                 │
│  ─────────────────────  |  ──────────────────────         │
│  • Text inclusion       |  • Single compilation            │
│  • Macro pollution      |  • No macro issues              │
│  • Rebuild everything   |  • Faster builds                │
│  • No encapsulation     |  • True encapsulation          │
│                                                             │
└─────────────────────────────────────────────────────────────┘

Basic Module

math.cppm

export module math;

export int add(int a, int b) {
    return a + b;
}

export int multiply(int a, int b) {
    return a * b;
}

Importing Modules

main.cpp

import math;

int main() {
    int result = add(5, 3);
    return 0;
}

Module Partitions

// math.cppm (primary module interface)
export module math;

export int add(int a, int b);

// Implementation partition
module math.implementation;

int helper(int x) {
    return x * 2;
}

Benefits

• Faster compilation
• No header guards needed
• True encapsulation
• No macro pollution

Key Takeaways

• Modules replace headers in modern C++
• Use .cppm extension for module interfaces
• Provides better encapsulation and faster builds