CODEWITHSUNDEEP
c++arraysperformancefunctionmemory
McLovin
McLovin

Reputation: 3417

Class methods variables, is it faster if I store them in the class itself?

Consider the next piece of code

class foo {
public:
  void f() { 
    char buffer[1024];
    memset(buffer, NULL, 1024);
    read_some_input_to_buffer(buffer, 1024);
  }
};

class bar {
public:
  void f() {
    memset(_myPrivateBuffer, NULL, 1024);
    read_some_input_to_buffer(_myPrivateBuffer, 1024);
  }

private:
  char _myPrivateBuffer[1024];
};

Will bar::f() work faster than foo::f()? As I see it, the buffer already exists in bar, so the compiler won't allocate memory for it on the stack when the function is called? Or am I wrong and the memory is already allocated before foo::f() is called as well?

Upvotes: 2

Views: 39

Answers (1)

gsamaras
gsamaras

Reputation: 73366

is it faster if I store them in the class itself?

No.

so the compiler won't allocate memory for it on the stack

Allocating memory on the stack is equivalent to moving the stack pointer. And more important, stack is always hot, the memory you get is much more likely to be in cache than any far heap allocated memory. Read more in Which is faster: Stack allocation or Heap allocation.

PS: Be careful not to become a victim of premature optimization.

Upvotes: 1

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