FindAtom with MAKEINTATOM useless? - c++

Question

as I understand it, FindAtom returns 0 if the requested Atom is not found. But even in this small code, without any AddAtom at all, it seems to always return something. Why is that? Doesn’t this make FindAtom with Ints useless? :confus:
int main( ) {
cout << FindAtom(MAKEINTATOM(12345)); // Output: 12345
cout << FindAtom(MAKEINTATOM(2011)); // Output: 2011
return 0;
}
Bye

Answer 1

Signature of the FindAtom function:
ATOM WINAPI FindAtom(
__in LPCTSTR lpString
);
I found the following code in Wine svn-repository. It represents the basic logic:
295 ATOM WINAPI FindAtom16( LPCSTR str )
296 {
297 ATOMTABLE * table;
298 WORD hash,iatom;
299 HANDLE16 entry;
300 int len;
301
302 TRACE("%s\n",debugstr_a(str));
303
304 if (ATOM_IsIntAtomA( str, &iatom )) return iatom;
305 if ((len = strlen( str )) > 255) len = 255;
306 if (!(table = ATOM_GetTable( FALSE ))) return 0;
307 hash = ATOM_Hash( table->size, str, len );
308 entry = table->entries[hash];
309 while (entry)
310 {
311 ATOMENTRY * entryPtr = ATOM_MakePtr( entry );
312 if ((entryPtr->length == len) &&
313 (!strncasecmp( entryPtr->str, str, len )))
314 {
315 TRACE("-- found %x\n", entry);
316 return HANDLETOATOM( entry );
317 }
318 entry = entryPtr->next;
319 }
320 TRACE("-- not found\n");
321 return 0;
322 }
So, let's try to trace the program, when it's calling the FindAtom function:
FindAtom(MAKEINTATOM(12345));
MAKEINTATOM is a macro:
#define MAKEINTATOM(i) (LPTSTR)((DWORD)((WORD)(i)))
MAKEINTATOM(12345) returns an integer atom cast to a string pointer.
Calling FindAtom(MAKEINTATOM(12345))
Checking the condition if (ATOM_IsIntAtomA( str, &iatom ))
119 static BOOL ATOM_IsIntAtomA(LPCSTR atomstr,WORD *atomid)
120 {
121 UINT atom = 0;
122 if (!HIWORD(atomstr)) atom = LOWORD(atomstr);
123 else
124 {
125 if (*atomstr++ != '#') return FALSE;
126 while (*atomstr >= '' && *atomstr <= '9')
127 {
128 atom = atom * 10 + *atomstr - '';
129 atomstr++;
130 }
131 if (*atomstr) return FALSE;
132 }
133 if (atom >= MAXINTATOM)
134 {
135 SetLastError( ERROR_INVALID_PARAMETER );
136 atom = 0;
137 }
138 *atomid = atom;
139 return TRUE;
140 }
As you can see this function will return a pointer to UINT when called with an argument which represents an integer atom.
Then it executes the body
return iatom;
So when you call cout << FindAtom (MAKEINTATOM (12345)); you get 12345 as output.