Which is Better

[baray98]

In case

//style A
 
for ( int i = 0 ; i < 1000 ; ++i)
{
   MyData data = getData();
  // do something with data
}
 
//style B
MyData data;
for ( int i = 0 ; i < 1000  ; ++i)
{
   data = getData();
  // do something with data
}

//style A

for ( int i = 0 ; i < 1000 ; ++i)
{
   MyData data = getData();
  // do something with data
}

//style B
MyData data;
for ( int i = 0 ; i < 1000  ; ++i)
{
   data = getData();
  // do something with data
}

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Would I gain a little speed using A or B?,
Which is one is more readable?

have a good weekend,
baray98

[caduel]

I would prefer A for readability. If the compiler properly uses RVO (return value optimization) it might be faster, too.

[wysota]

The speed might be different depending if you have copy constructor and assignment operators defined for your class. But in general the speed difference is so small you can ignore it.

[hkvm]

If the variable "data" is only going to be used in the loop then definitely style A. If it's going to be used outside, you don't have a choice anyway. I don't see a reason to put variables into wider scope than necessary, you need to keep track of it longer which hurts readability rather than helps.