Fix #895 (false positive: Suspicious pointer subtraction)

http://sourceforge.net/apps/trac/cppcheck/ticket/895

lib/checkclass.cpp

@@ -865,16 +865,20 @@ void CheckClass::thisSubtractionError(const Token *tok)
 
 void CheckClass::thisSubtraction()
 {
-    const Token *tok = Token::findmatch(_tokenizer->tokens(), "this - %var%");
-    if (tok)
+    const Token *tok = _tokenizer->tokens();
+    for (;;)
     {
-        thisSubtractionError(tok);
+        tok = Token::findmatch(tok, "this - %var%");
+        if (!tok)
+            break;
+
+        if (!Token::simpleMatch(tok->previous(), "*"))
+            thisSubtractionError(tok);
+
+        tok = tok->next();
     }
 }
 
-
-
-
 void CheckClass::noConstructorError(const Token *tok, const std::string &classname)
 {
     reportError(tok, Severity::style, "noConstructor", "The class '" + classname + "' has no constructor. Member variables not initialized.");

test/testclass.cpp

@@ -758,6 +758,14 @@ private:
     {
         checkThisSubtraction("; this-x ;");
         ASSERT_EQUALS("[test.cpp:1]: (possible style) Suspicious pointer subtraction\n", errout.str());
+
+        checkThisSubtraction("; *this = *this-x ;");
+        ASSERT_EQUALS("", errout.str());
+
+        checkThisSubtraction("; *this = *this-x ;\n"
+                             "this-x ;");
+        ASSERT_EQUALS("[test.cpp:2]: (possible style) Suspicious pointer subtraction\n", errout.str());
+
     }
 };