c stl vector move semantics-CodePudding

To enable move semantics on a C stl vector do I need to pass by value so the compiler will not copy the element but just move them?

Example:

class data
{
    void setMyData(vector<string> sourceData){private_data_=sourceData;}

    private:
    vector<string> private_data_;
}

CodePudding user response：

to enable move semantics on a C stl vector

You have misunderstanding about the move semantic concept.

The std::vector itself is move constructable as it has the move constructor defined. You do not need to enable it explicitly, rather use it properly.

In the function

void setMyData(vector<string> sourceData)  // copy 1
{
   private_data_= sourceData; // copy 2
}

You are doing double copy. You need instead

void setMyData(vector<string> sourceData)  // copy 
{
   private_data_= std::move(sourceData); // move
}

or you might want

void setMyData(vector<string>&& sourceData)  // only accept the rvalue
{
   private_data_= std::move(sourceData); // move
}

and for the second case, you call the function

setMyData(std::move(sourceData));

CodePudding user response：

I would recommend either using 2 overload of that function or even use a generic one:

#include <vector>
#include <string>

class data
{
public:
    void setMyData(const std::vector<std::string>& sourceData){private_data_=sourceData;}

    void setMyData(std::vector<std::string>&& sourceData){private_data_= std::move(sourceData);}

    template <typename T>
    void genericsetMyData(T&& source) {private_data_ = std::forward<T>(source);}

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

int main() {
    class data a,b,c,d;
    std::vector<std::string> s1,s2; const std::vector<std::string> s3;
    a.setMyData(s1);
    b.setMyData(std::move(s2));
    c.genericsetMyData(s1);
    d.genericsetMyData((std::move(s1)));
    d.genericsetMyData(s3);
}

The templated one is a bit more complex since it uses a so called fowarding reference.