Fixed #4203 (Don't warn about setting NULL value for pointers and not using that value)

.travis.yml

@@ -5,4 +5,4 @@ compiler:
 script:
   - make test
   - $CXX -o cppcheck -O2 cli/*.cpp lib/*.cpp -Ilib
-  - ./cppcheck --error-exitcode=1 -Ilib --enable=style --suppress=unreadVariable --suppress=duplicateBranch --suppress=stlIfStrFind -q cli gui lib -igui/test
+  - ./cppcheck --error-exitcode=1 -Ilib --enable=style --suppress=duplicateBranch --suppress=stlIfStrFind -q cli gui lib -igui/test

lib/checkunusedvar.cpp

@@ -250,7 +250,7 @@ void Variables::write(unsigned int varid, const Token* tok)
 
     if (usage) {
         usage->_write = true;
-        if (!usage->_var->isStatic())
+        if (!usage->_var->isStatic() && !Token::simpleMatch(tok->next(), "= 0 ;"))
             usage->_read = false;
         usage->_lastAccess = tok;
     }

test/testunusedvar.cpp

@@ -144,6 +144,7 @@ private:
         TEST_CASE(localvarIfNOT);    // #3104 - if ( NOT var )
         TEST_CASE(localvarAnd);      // #3672
         TEST_CASE(localvarSwitch);   // #3744 - false positive when localvar is used in switch
+        TEST_CASE(localvarNULL);     // #4203 - Setting NULL value is not redundant - it is safe
 
         TEST_CASE(crash1);
     }
@@ -3317,6 +3318,16 @@ private:
         ASSERT_EQUALS("", errout.str());
     }
 
+    void localvarNULL() { // #4203 - Setting NULL value is not redundant - it is safe
+        functionVariableUsage("void f() {\n"
+                              "    char *p = malloc(100);\n"
+                              "    foo(p);\n"
+                              "    free(p);\n"
+                              "    p = NULL;\n"
+                              "}");
+        ASSERT_EQUALS("", errout.str());
+    }
+
     void crash1() {
         functionVariableUsage("SAL_WNODEPRECATED_DECLARATIONS_PUSH\n"
                               "void convertToTokenArray() {\n"