c++ - Using local variable assigned to return value of a function or using function directly -

c++ - Using local variable assigned to return value of a function or using function directly -

is there difference between this:

myclass c = getmyclass(); calculate(c.value);

and this:

calculate(getmyclass().value);

in scope of performance , memory allocation?

yes, there serious difference. in first case, c lvalue, , not destroyed until end of scope. can delay useful things reosurce cleanup. more problematically, beingness lvalue means cannot moved, must copied, inefficient many classes downright illegal of import classes, unique_ptr.

in sec case, compiler cleans temporary right away, resources released promptly, , beingness rvalue gives compiler more freedom optimize , permits move semantics.

this still true when value fellow member or fellow member function, result of both can inherit value category parent object.

you should scope objects minimum scope required, , if don't need access c later, should utilize temporary.

c++ performance compiler-construction