Read a variant only when it holds the expected type.

C++: get_if returns a null pointer rather than throwing for another active alternative.

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;
    std::variant<int,std::string> value=std::string("hello");
    if (const auto* text=std::get_if<std::string>(&value)) std::cout << *text << "\n";
}

Expected output EXAMPLE

hello

Details

Save as snippet.cpp; compile with g++ -std=c++17 -Wall -Wextra snippet.cpp -pthread -o snippet, then run ./snippet. get_if returns a null pointer rather than throwing for another active alternative.

✓ 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
143fa2238e818617b0d2eb6871b74c039f6647c3b3e8d1158351f5f51973cd4e
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

hello

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