Organizing a multi-file project | C++

Real C++ programs need organization. Good structure makes ownership, dependencies, and build targets easier to understand.

Simple project layout

tasklog/
  CMakeLists.txt
  include/
    tasklog/
      task.h
      parser.h
  src/
    task.cpp
    parser.cpp
    main.cpp
  tests/
    parser_tests.cpp

Public headers live under include/tasklog. Implementation lives under src. Tests live under tests.

Small projects can use simpler layouts, but keep interfaces and implementation distinct.

Headers expose contracts

Headers should contain declarations and small type definitions that other files need:

// include/tasklog/task.h
#pragma once

#include <string>

namespace tasklog {

struct Task {
    std::string title;
    bool done{};
};

}

Keep headers focused. Every include in a header spreads to files that include it.

Source files define behavior

// src/parser.cpp
#include "tasklog/parser.h"

namespace tasklog {

std::optional<Task> parse_task(std::string_view line) {
    // implementation
}

}

Source files can include heavier dependencies without forcing them into every caller.

Namespaces

Namespaces group project code and avoid name collisions:

namespace tasklog {
    // project types and functions
}

Use project namespaces early. Avoid putting your own names into std.

Tests and tools

Even small C++ projects benefit from:

debug builds
sanitizer builds
focused tests for parsing and business rules
warnings enabled
formatting choices applied consistently

Testing does not replace understanding lifetime and ownership, but it catches regressions.

What to carry forward

separate public headers from implementation when projects grow
headers expose contracts and should stay focused
source files define behavior
namespaces prevent naming collisions
tests, warnings, and sanitizers belong in normal workflow

Next, you will design a capstone project that uses the course’s main ideas together.