Question

In the wake of this question about static methods in managed code, I’m interesting if the answers there is relevant to unmanaged code like c++.

I make thousands of instances, and my question is mainly about static methods. Do this methods save memory compared regular methods?

thank you, and sorry about my poor English.

Answer 1

All methods require their binary code to be in memory in order to run. The executable code for static and non-static methods is (largely) the same.

Both types of methods require only one place in memory, so they’re not replicated with every instance of the class.

Let’s now take a look at some code:

class A
{
public:
   void foo();
   static void goo();
};

void A::foo()
{
004113D0  push        ebp  
004113D1  mov         ebp,esp 
004113D3  sub         esp,0CCh 
004113D9  push        ebx  
004113DA  push        esi  
004113DB  push        edi  
004113DC  push        ecx  
004113DD  lea         edi,[ebp-0CCh] 
004113E3  mov         ecx,33h 
004113E8  mov         eax,0CCCCCCCCh 
004113ED  rep stos    dword ptr es:[edi] 
004113EF  pop         ecx  
004113F0  mov         dword ptr [ebp-8],ecx 
}
004113F3  pop         edi  
004113F4  pop         esi  
004113F5  pop         ebx  
004113F6  mov         esp,ebp 
004113F8  pop         ebp  
004113F9  ret     


void A::goo()
{
00411530  push        ebp  
00411531  mov         ebp,esp 
00411533  sub         esp,0C0h 
00411539  push        ebx  
0041153A  push        esi  
0041153B  push        edi  
0041153C  lea         edi,[ebp-0C0h] 
00411542  mov         ecx,30h 
00411547  mov         eax,0CCCCCCCCh 
0041154C  rep stos    dword ptr es:[edi] 
}
0041154E  pop         edi  
0041154F  pop         esi  
00411550  pop         ebx  
00411551  mov         esp,ebp 
00411553  pop         ebp  
00411554  ret           



int main()
{
   A a;
   a.foo();
0041141E  lea         ecx,[a] 
00411421  call        foo (4111E5h) 
   a.goo();
00411426  call        A::goo (4111EAh) 
   return 0;
}

There are only minor differences, such as pushing the this pointer onto the stack for the non-static function, but they are minor, and probably a decent optimizer will reduce the differences even further.

A decision about whether or not to use static functions should be strictly design-driven, not memory-driven.