difference in initialization constructor

Question

I have a simple class with two objects in main(). Are there any differences in the initialization of the constructor ?

//#include <systemd/sd-bus.h> #include <iostream> #include <memory> class Simple { private: int a; public: Simple(int b) : a(b) { } void show() { std::cout << a; } }; int main() { Simple firstObj = Simple(5); firstObj.show(); Simple secondObj(5); secondObj.show(); return 0; }

Jarod42 · Accepted Answer · 2022-01-19 10:28:28Z

3

Pre-C++17,

first one uses also copy(Pre-c++11)/move constructor (which might be elided) whereas second uses only Simple(int).
Since C++17,

both are equivalent.

edited Jan 19, 2022 at 10:28

answered Jan 19, 2022 at 10:23

Jarod42

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1 Comment

eerorika Over a year ago

Your Pre-C++17 description is a Pre-C++11 description. [C++11, C++17) description is same except move constructor would be used.

songyuanyao · Accepted Answer · 2022-01-19 10:24:10Z

Simple firstObj = Simple(5); performs copy initialization, Simple secondObj(5); performs direct initialization, since C++17 they have the exact same effect: the object is initialized by the constructor Simple::Simple(int) directly.

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