C++ 核心准则与专业模式

#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <span>
#include <stdexcept>

// R.1: Manage resources automatically using RAII
class DatabaseConnection {
public:
    explicit DatabaseConnection(const std::string& connection_string) {
        // Acquire resource in constructor
        std::cout << "Connected to: " << connection_string << "\n";
    }
    ~DatabaseConnection() {
        // Release resource in destructor — always runs
        std::cout << "Disconnected\n";
    }

    // Rule of 5: if you define a destructor, define or delete all 5
    DatabaseConnection(const DatabaseConnection&) = delete;
    DatabaseConnection& operator=(const DatabaseConnection&) = delete;
    DatabaseConnection(DatabaseConnection&&) noexcept = default;
    DatabaseConnection& operator=(DatabaseConnection&&) noexcept = default;

    void query(std::string_view sql) const {
        std::cout << "Executing: " << sql << "\n";
    }
};

// I.4: Make interfaces precisely and strongly typed
// BAD: void process(int type, void* data, int size);
// GOOD:
enum class DataType { json, xml, csv };

void process(DataType type, std::span<const std::byte> data) {
    // type-safe, no raw pointers, size is carried with the data
}

// F.3: Keep functions short and simple
[[nodiscard]] bool is_valid_email(std::string_view email) {
    auto at_pos = email.find('@');
    if (at_pos == std::string_view::npos) return false;
    auto dot_pos = email.find('.', at_pos);
    return dot_pos != std::string_view::npos && dot_pos > at_pos + 1;
}

int main() {
    // R.5: Prefer scoped objects — no unnecessary heap allocation
    DatabaseConnection db("host=localhost dbname=mydb");
    db.query("SELECT * FROM users");
    // db is automatically closed when it goes out of scope

    // R.11: Avoid raw new/delete — use smart pointers
    auto widget = std::make_unique<std::vector<int>>(100);

    std::cout << is_valid_email("user@example.com") << "\n";   // 1
    std::cout << is_valid_email("invalid-email") << "\n";       // 0

    return 0;
}

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>

class StudentRegistry {
public:
    // const method — promises not to modify the object
    [[nodiscard]] size_t count() const { return students_.size(); }

    // const reference return — caller can read but not modify
    [[nodiscard]] const std::string& get_name(size_t index) const {
        if (index >= students_.size())
            throw std::out_of_range("Invalid student index");
        return students_[index];
    }

    // Non-const method — modifies the object
    void add_student(std::string name) {
        students_.push_back(std::move(name));
    }

    // const-correct algorithm usage
    [[nodiscard]] bool has_student(std::string_view name) const {
        return std::any_of(students_.cbegin(), students_.cend(),
            [name](const std::string& s) { return s == name; });
    }

private:
    std::vector<std::string> students_;
};

void print_registry(const StudentRegistry& reg) {
    // Can only call const methods on a const reference
    for (size_t i = 0; i < reg.count(); ++i) {
        std::cout << reg.get_name(i) << "\n";
    }
    // reg.add_student("Eve");  // ERROR: cannot call non-const method
}

int main() {
    StudentRegistry reg;
    reg.add_student("Alice");
    reg.add_student("Bob");

    print_registry(reg);

    // const local variables
    const auto count = reg.count();  // immutable
    const auto& name = reg.get_name(0);  // immutable reference

    std::cout << "Count: " << count << ", First: " << name << "\n";

    return 0;
}

# Linux: perf — hardware performance counters
perf record -g ./my_program         # record call graph
perf report                           # interactive flamegraph viewer

# Linux: perf stat — high-level statistics
perf stat ./my_program
# Output: cycles, instructions, cache misses, branch misses, IPC

# macOS: Instruments (via Xcode)
xcrun xctrace record --template 'Time Profiler' --launch ./my_program

# Cross-platform: Google Benchmark (micro-benchmarking)
# In your code:
#include <benchmark/benchmark.h>

static void BM_VectorPushBack(benchmark::State& state) {
    for (auto _ : state) {
        std::vector<int> v;
        for (int i = 0; i < state.range(0); ++i) {
            v.push_back(i);
        }
        benchmark::DoNotOptimize(v.data());
    }
}
BENCHMARK(BM_VectorPushBack)->Range(8, 1 << 16);

static void BM_VectorReserved(benchmark::State& state) {
    for (auto _ : state) {
        std::vector<int> v;
        v.reserve(state.range(0));
        for (int i = 0; i < state.range(0); ++i) {
            v.push_back(i);
        }
        benchmark::DoNotOptimize(v.data());
    }
}
BENCHMARK(BM_VectorReserved)->Range(8, 1 << 16);

BENCHMARK_MAIN();