Thread: Hammer, a question for you - var scope

>but is it part of the C standard or the C++ standard?
I'm not sure about the C++ standard, but I'm quite sure about C89 and most likely C99 as well. I would have to assume that it is supported in C++ for compatibility with C though.

>print out a dissassembly and post it?
Gladly, I had to modify the program so that it would actually compile, so the disassembly of the following code:

Code:

#include <stdio.h>

int main ( void )
{
  int a = 2;
  {
    int a = 0;
    a++;
  }
  printf ( "%d\n", a );
  return 0;
}

Which gives me one warning in Lint:

Code:

cTest.c: (in function main)
cTest.c(7,9): Variable a shadows outer declaration
  An outer declaration is shadowed by the local declaration. (Use -shadow to
  inhibit warning)
   cTest.c(5,7): Previous definition of a: int

Is as follows for MSVC++ 6:

Code:

1:    #include <stdio.h>
2:
3:    int main ( void )
4:    {
00401000   push        ebp
00401001   mov         ebp,esp
00401003   sub         esp,48h
00401006   push        ebx
00401007   push        esi
00401008   push        edi
00401009   lea         edi,[ebp-48h]
0040100C   mov         ecx,12h
00401011   mov         eax,0CCCCCCCCh
00401016   rep stos    dword ptr [edi]
5:      int a = 2;
00401018   mov         dword ptr [ebp-4],2
6:      {
7:        int a = 0;
0040101F   mov         dword ptr [a],0
8:        a++;
00401026   mov         eax,dword ptr [a]
00401029   add         eax,1
0040102C   mov         dword ptr [a],eax
9:      }
10:     printf ( "%d\n", a );
0040102F   mov         ecx,dword ptr [ebp-4]
00401032   push        ecx
00401033   push        offset string "%d\n" (0040c01c)
00401038   call        printf (00401060)
0040103D   add         esp,8
11:     return 0;
00401040   xor         eax,eax
12:   }
00401042   pop         edi
00401043   pop         esi
00401044   pop         ebx
00401045   add         esp,48h
00401048   cmp         ebp,esp
0040104A   call        __chkesp (004010e0)
0040104F   mov         esp,ebp
00401051   pop         ebp
00401052   ret

-Prelude

Glad to see you've been having fun without me

>Seemingly, to create additional layers of scope as this change adopts can only mean that the stackframe has to be larger than it otherwise would be, because although the variable names could be the same inside and outside of braces, separate data spaces must be allocated for each. Kinda foolish, I think.<

To re-iterate Salems point, scope is a language feature and wouldn't necessarily have to have a bearing on the asm that is produced, unless you're trying to produce asm from the C source code that follows scope rules. However, this may mean that something like -

Code:

#include <stdio.h>

int main()
{
	int* ptr;

	{
		int a=10;
		ptr=&a;
	}

	printf("%d",*ptr);

	return 0;
}

would always work, even though 'a' is out of scope.