DDE 31c C compiler bug

The program below prints ‘test1’ – it shouldn’t print anything.

I tried other old compiler versions it’s still there at DDE27 – probably always been there.

Change the name in main to _e and ‘test3’ is printed.

In 2 minds as to whether it is a trap or a bug.

#include <stdlib.h>
#include <stdio.h>
#include "swis.h"

#define test1(er) \
    do \
    { \
        _kernel_oserror* e = (er); \
        if (e != NULL) \
        {\
            printf("test1\n");\
        } \
    } while (0)

#define test2(e) \
    do \
    { \
        if (e != NULL) \
        {\
            printf("test2\n");\
        } \
    } while (0)
    
#define test3(er) \
    do \
    { \
        _kernel_oserror* _e = (er); \
        if (_e != NULL) \
        {\
            printf("test3\n");\
        } \
    } while (0)



int main(void)
{
  _kernel_oserror* e = NULL;
  test1(e);
  test2(e);
  test3(e);
  return 0;
}

They joys of macro substitution vs inline functions, huh?

Write out what the compiler preprocessor would produce:

int main(void)
{
  _kernel_oserror* e = NULL;
  // vv for test1(e);
  do
    {
        _kernel_oserror* e = e;
        if (e != NULL)
        {
            printf("test1\n");
        }
    } while (0);
  ...  
  return 0;
}

Which e? The one in that block.

And a gentle reminder that C’s roles on what local scope is isn’t the same as BASIC. ;)