C++ Cheatsheet

Overview #

This note is a practical reference for commonly used C++ snippets and core concepts.

The focus is on:

• Day-to-day development workflows
• Short explanations that clarify when and why something is used
• Examples that reflect real-world usage rather than exhaustive documentation

std::span (C++20) #

What it is

• Non-owning view over contiguous memory

• Works with:

  • C-style arrays
  • std::array
  • std::vector

Why use it

• Avoids templating functions on container types
• Prevents tight coupling between APIs and containers
• Improves readability and flexibility of function signatures

Key properties

• No memory ownership
• No allocation or resizing
• Read-only or mutable (std::span<T> vs std::span<const T>)

Common APIs

• span.size() — number of elements
• span.data() — pointer to data
• span.subspan(offset, count) — view into a subset

Example

void print_names(std::span<const std::string> names)
{
    for (const auto& n : names)
        std::cout << n << '\n';
}

int main()
{
    const std::string raw[] = {"John", "Alex"};
    std::vector<std::string> vec = {"Jordan", "Jack"};
    std::array<std::string, 2> arr = {"Kevin", "Kirye"};

    print_names(raw);
    print_names(vec);
    print_names(arr);
}

Rules of thumb

• Use std::span for function parameters
• Never store std::span beyond the lifetime of the data
• Prefer std::span<const T> for read-only access

Time Measurement (Elapsed Time) #

Use when: Measuring execution time of a code block.

#include <chrono>
#include <iostream>

auto start = std::chrono::steady_clock::now();

// code to measure

auto end = std::chrono::steady_clock::now();

auto elapsed = std::chrono::duration_cast<std::chrono::milliseconds>(
    end - start
);

std::cout << elapsed.count() << " ms\n";

Key points

• steady_clock → monotonic, safe for timing
• duration_cast<T> → convert to desired unit
• count() → numeric value

Common units

std::chrono::nanoseconds
std::chrono::microseconds
std::chrono::milliseconds
std::chrono::seconds

🧠 Quick Reminder #