Fixed #375 (new check: Detect when using 'this-x')

src/checkclass.cpp

@@ -851,6 +851,21 @@ void CheckClass::virtualDestructor()
 }
 //---------------------------------------------------------------------------
 
+void CheckClass::thisSubtractionError(const Token *tok)
+{
+    reportError(tok, Severity::possibleStyle, "thisSubtraction", "Suspicious pointer subtraction");
+}
+
+void CheckClass::thisSubtraction()
+{
+    const Token *tok = Token::findmatch(_tokenizer->tokens(), "this - %var%");
+    if (tok)
+    {
+        thisSubtractionError(tok);
+    }
+}
+
+
 
 
 void CheckClass::noConstructorError(const Token *tok, const std::string &classname)

src/checkclass.h

@@ -57,6 +57,8 @@ public:
             checkClass.constructors();
             checkClass.operatorEq();
             checkClass.privateFunctions();
+            if (settings->_showAll)
+                checkClass.thisSubtraction();
         }
         checkClass.virtualDestructor();
     }
@@ -79,6 +81,7 @@ public:
     // The destructor in a base class should be virtual
     void virtualDestructor();
 
+    void thisSubtraction();
 private:
     class Var
     {
@@ -111,6 +114,7 @@ private:
     void memsetStructError(const Token *tok, const std::string &memfunc, const std::string &classname);
     void operatorEqReturnError(const Token *tok);
     void virtualDestructorError(const Token *tok, const std::string &Base, const std::string &Derived);
+    void thisSubtractionError(const Token *tok);
 
     void getErrorMessages()
     {
@@ -122,6 +126,7 @@ private:
         memsetStructError(0, "memfunc", "classname");
         operatorEqReturnError(0);
         virtualDestructorError(0, "Base", "Derived");
+        thisSubtractionError(0);
     }
 
     std::string name() const

test/testclass.cpp

@@ -58,13 +58,14 @@ private:
         TEST_CASE(uninitVarHeader3);    // Class is defined in header
         TEST_CASE(uninitVarPublished);  // Variables in the published section are auto-initialized
 
-
         TEST_CASE(noConstructor1);
         TEST_CASE(noConstructor2);
 
         TEST_CASE(operatorEq1);
         TEST_CASE(memsetOnStruct);
         TEST_CASE(memsetOnClass);
+
+        TEST_CASE(this_subtraction);    // warn about "this-x"
     }
 
     // Check the operator Equal
@@ -724,6 +725,32 @@ private:
                       "}\n");
         ASSERT_EQUALS("[test.cpp:10]: (error) Using 'memset' on struct that contains a 'std::string'\n", errout.str());
     }
+
+
+    void checkThisSubtraction(const char code[])
+    {
+        // Tokenize..
+        Tokenizer tokenizer;
+        std::istringstream istr(code);
+        tokenizer.tokenize(istr, "test.cpp");
+        tokenizer.simplifyTokenList();
+
+        // Clear the error log
+        errout.str("");
+
+        // Check..
+        Settings settings;
+        settings._checkCodingStyle = true;
+        settings._showAll = true;
+        CheckClass checkClass(&tokenizer, &settings, this);
+        checkClass.thisSubtraction();
+    }
+
+    void this_subtraction()
+    {
+        checkThisSubtraction("; this-x ;");
+        ASSERT_EQUALS("[test.cpp:1]: (possible style) Suspicious pointer subtraction\n", errout.str());
+    }
 };
 
 REGISTER_TEST(TestClass)