Capture configuration by value in a callable.

C++: A value capture retains the value from lambda creation even if the original variable changes later.

C++ snippet.cpp
#include <iostream>
#include <string>
#include <string_view>
#include <vector>
#include <array>
#include <algorithm>
#include <numeric>
#include <map>
#include <unordered_map>
#include <set>
#include <queue>
#include <stack>
#include <deque>
#include <tuple>
#include <bitset>
#include <memory>
#include <optional>
#include <variant>
#include <functional>
#include <charconv>
#include <regex>
#include <fstream>
#include <sstream>
#include <filesystem>
#include <iomanip>
#include <cmath>
#include <cctype>
#include <limits>
#include <chrono>
#include <thread>
#include <future>
#include <mutex>
#include <atomic>
#include <condition_variable>

int main() {
    std::cout << std::boolalpha;
    int factor=3;
    auto multiply=[factor](int value){return factor*value;};
    factor=10;
    std::cout << multiply(4) << " " << factor << "\n";
}

Expected output EXAMPLE

12 10

Details

Save as snippet.cpp; compile with g++ -std=c++17 -Wall -Wextra snippet.cpp -pthread -o snippet, then run ./snippet. A value capture retains the value from lambda creation even if the original variable changes later.

✓ Verified

Tested on Ubuntu 24.04.5 LTS · · g++ (Ubuntu 13.3.0-6ubuntu2~24.04.1) 13.3.0 · g++ 4:13.2.0-7ubuntu1

Test inputs, results and environment

The exact published code ran in a dedicated Linux test container with prepared inputs. Unprivileged snippet process, external networking disabled, read-only root filesystem, and a fresh temporary working directory. Fixtures and output records are isolated from the application database. Testing covers this example and its stated checks, not every input, operating system, or runtime version. The Linux container shares its host's kernel; this is not a native Windows test.

Architecture / host kernel
x86_64 / 6.18.54.1-microsoft-standard-WSL2
Snippet identity / locale
uid=65534, gid=65534 (unprivileged) / C.UTF-8
Interpreter invocation
g++ -std=c++17 -Wall -Wextra -Werror snippet.cpp -pthread -lm -o snippet && ./snippet
Container image ID
sha256:32dc2d998158b6554c99b73b533f423696a0f3e31e8cbea9db10b5eee9a2fadd
Code SHA-256
c0430acfa907dad3efa6778e1a0f920062b438cac56aa6e82470759c607cb28c
Dependencies
g++ 4:13.2.0-7ubuntu1

Test input setup

These are the prepared inputs used by the test harness. See Details above for the prerequisites and how to run this example.

# No input files required.

Observed standard output

12 10

Exit code: 0. Standard error: empty. Validation: Exact stdout comparison. System-dependent values above are one recorded run.