Temporary function object in a for loop
Does the function object randomElementByWeight constructor get called for every iteration through the loop or can the compiler optimize this away somehow? I want to make sure the rand function is called for each iter开发者_运维技巧ation and I think it's nicer to have it in the function object constructor.
struct randomElementByWeight
{
double randomNumber;
randomElementByWeight() : randomNumber(rand() / static_cast<double>(RAND_MAX)) {}
bool operator()(const Element& e)
{
if ( (randomNumber -= e.weight) <= 0.0 )
{
return true;
}
return false;
}
};
...
for (int i = 0; i < 3; ++i)
{
iter = find_if(routes.begin(), routes.end(), randomElementByWeight());
}
Yes it does, a constructor is always called for a temporary variable. Unless the compiler knows absolutely sure there are no side-effects if ommitted it won't optimize it away.
Just a side note, the following code:
if ( (randomNumber -= e.weight) <= 0.0 )
{
return true;
}
return false;
can be abbreviated to:
return (randomNumber -= e.weight) <= 0.0;
精彩评论