return-by-value | 易学教程

Returning Vectors standard in C++

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Now, I know this is a common question, but I haven't been able to really find a straight answer on this. This is really a question about standards. I am working on a project involving the genetic algorithm. But I'm running into a bottleneck when it comes to returning a vector. Is there a "proper" way to do this. Normally I use dynamically allocated arrays, and return a pointer to a newly created array. obj* func(obj* foo); That way, everything is efficient and there is no copying of data. Is there an equivalent to doing this with a vector? This vector has objects in it, so returning it by

Why is copy constructor not called

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问题 Here is a simple class header file and a main program. In the main program, I thought that the copy constructor is called in exactly three situations: initialization(explicit copy), pass by value for function arguments, and return by value for functions. However it seems like it is not being called for one of them, I think either (3) or (4) as numbered in the comments. For which numbers (1) - (4) does it get called? Thanks. X.h: #include <iostream> class X { public: X() {std::cout << "default

Why is the copy constructor called when we return an object from a method by value

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问题 why copy constructor is called when we return an object from a method by value. please see my below code in that i am returning an object from a method while returning control is hitting the copy constructor and then returning. i am not understood following things: 1) why it is calling copy constructor. 2)which object is passing implicitly to copy constructor, 3)to which object copy constructor will copy the content, 4)what is the necessity of copying the object content while returning. so

value semantics vs output params with large data structures

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2013 Keynote: Chandler Carruth: Optimizing the Emergent Structures of C++ 42:45 You don't need output parameters, we have value semantics in C++. ... Anytime you see someone arguing that nonono I'm not going to return by value because copy would cost too much, someone working on an optimizer says they're wrong. All right? I have never yet seen a piece of code where that argument was correct. ... People don't realize how important value semantics are to the optimizer because it completely clarifies the aliasing scenarios. Can anyone put this in the context of this answer: https://stackoverflow

value semantics vs output params with large data structures

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问题 2013 Keynote: Chandler Carruth: Optimizing the Emergent Structures of C++ 42:45 You don't need output parameters, we have value semantics in C++. ... Anytime you see someone arguing that nonono I'm not going to return by value because copy would cost too much, someone working on an optimizer says they're wrong. All right? I have never yet seen a piece of code where that argument was correct. ... People don't realize how important value semantics are to the optimizer because it completely