test17.c: In function 'func2':
test17.c:18:14: warning: comparison between pointer and integer
     if (ptr1 == (123, 0))
              ^
test17.c:20:15: warning: Using variable 'ptr1' without checking for null pointer
     ptr1->val = 100;
               ^
test17.c:20:15: warning: Using variable 'ptr1' without checking for null pointer
test17.c: In function 'func3':
test17.c:26:14: warning: comparison between pointer and integer
     if (ptr1 != (123, 0))
              ^
test17.c:28:15: warning: Using variable 'ptr1' without checking for null pointer
     ptr1->val = 100;
               ^
test17.c:28:15: warning: Using variable 'ptr1' without checking for null pointer
test17.c: In function 'func4':
test17.c:40:15: warning: Using variable 'ptr1' without checking for null pointer
     ptr1->val = 100;
               ^
test17.c:40:15: warning: Using variable 'ptr1' without checking for null pointer