Fixed #4734 (False 'Possible null pointer dereference')

lib/checknullpointer.cpp

@@ -762,6 +762,19 @@ void CheckNullPointer::nullPointerByDeRefAndChec()
             // Variable id for pointer
             const unsigned int varid(vartok->varId());
 
+            // bailout for while scope if pointer is assigned inside the loop
+            if (i->type == Scope::eWhile) {
+                bool assign = false;
+                for (const Token *tok2 = i->classStart; tok2 && tok2 != i->classEnd; tok2 = tok2->next()) {
+                    if (Token::Match(tok2, "%varid% =", varid)) {
+                        assign = true;
+                        break;
+                    }
+                }
+                if (assign)
+                    continue;
+            }
+
             // Name of pointer
             const std::string& varname(vartok->str());
 

test/testnullpointer.cpp

@@ -587,6 +587,19 @@ private:
               "}");
         TODO_ASSERT_EQUALS("error", "", errout.str());
 
+        // while
+        check("void f(int *p) {\n"
+              "    *p = 0;\n"
+              "    while (p) { p = 0; }\n"
+              "}");
+        ASSERT_EQUALS("", errout.str());
+
+        check("void f(int *p) {\n"
+              "    *p = 0;\n"
+              "    while (p) { }\n"
+              "}");
+        ASSERT_EQUALS("[test.cpp:2] -> [test.cpp:3]: (warning) Possible null pointer dereference: p - otherwise it is redundant to check it against null.\n", errout.str());
+
         // Ticket #3125
         check("void foo(ABC *p)\n"
               "{\n"