std::vector の実験

std::vector を少し高速化する - ひでたそ覚書帳 の実証実験

• copy constructor のみ
• move constructor を追加
• noexcept を追加

copy constructor のみ

#include <iostream>
#include <vector>

struct S {
    /*default constructor*/
    S() : id(counter++) {
        std::cout << "create id=" << id << std::endl;
    }

    /*copy constructor*/
    S(const S& rhs) : id(counter++) {
        std::cout << "copy id=" << id << " from id=" << rhs.id << std::endl;
    }

    /*destructor*/
    ~S() {
        std::cout << "delete id=" << id << std::endl;
    }

    int id;
    static int counter;
};
int S::counter = 0;

int main() {
    std::vector<S> v{};
    
    std::cout << "[simple append]" << std::endl;
    v.push_back(S{});

    std::cout << std::endl;

    std::cout << "[reallocate & append]" << std::endl;
    v.push_back(S{});

    std::cout << std::endl;
    std::cout << "[finish]" << std::endl;
    return 0;
}

output

[simple append]
create id=0
copy id=1 from id=0
delete id=0

[reallocate & append]
create id=2
copy id=3 from id=2
copy id=4 from id=1
delete id=1
delete id=2

[finish]
delete id=4
delete id=3

move constructor を追加

#include <iostream>
#include <vector>

struct S {
    /*default constructor*/
    S() : id(counter++) {
        std::cout << "create id=" << id << std::endl;
    }

    /*copy constructor*/
    S(const S& rhs) : id(counter++) {
        std::cout << "copy id=" << id << " from id=" << rhs.id << std::endl;
    }

    /*move constructor*/
    S(S&& rhs) : id(counter++) {
        std::cout << "move id=" << id << " from id=" << rhs.id << std::endl;
    }

    /*destructor*/
    ~S() {
        std::cout << "delete id=" << id << std::endl;
    }

    int id;
    static int counter;
};
int S::counter = 0;

int main() {
    std::vector<S> v{};
    
    std::cout << "[simple append]" << std::endl;
    v.push_back(S{});

    std::cout << std::endl;

    std::cout << "[reallocate & append]" << std::endl;
    v.push_back(S{});

    std::cout << std::endl;
    std::cout << "[finish]" << std::endl;
    return 0;
}

output

[simple append]
create id=0
move id=1 from id=0
delete id=0

[reallocate & append]
create id=2
move id=3 from id=2
copy id=4 from id=1
delete id=1
delete id=2

[finish]
delete id=4
delete id=3

noexcept を追加

#include <iostream>
#include <vector>

struct S {
    /*default constructor*/
    S() : id(counter++) {
        std::cout << "create id=" << id << std::endl;
    }

    /*copy constructor*/
    S(const S& rhs) : id(counter++) {
        std::cout << "copy id=" << id << " from id=" << rhs.id << std::endl;
    }

    /*move constructor*/
    S(S&& rhs) noexcept : id(counter++) {
        std::cout << "move id=" << id << " from id=" << rhs.id << std::endl;
    }

    /*destructor*/
    ~S() {
        std::cout << "delete id=" << id << std::endl;
    }

    int id;
    static int counter;
};
int S::counter = 0;

int main() {
    std::vector<S> v{};
    
    std::cout << "[simple append]" << std::endl;
    v.push_back(S{});

    std::cout << std::endl;

    std::cout << "[reallocate & append]" << std::endl;
    v.push_back(S{});

    std::cout << std::endl;
    std::cout << "[finish]" << std::endl;
    return 0;
}

output

[simple append]
create id=0
move id=1 from id=0
delete id=0

[reallocate & append]
create id=2
move id=3 from id=2
move id=4 from id=1
delete id=1
delete id=2

[finish]
delete id=4
delete id=3