Fixed #959 (new check: wrong usage of fflush())

lib/checkother.cpp

@@ -254,6 +254,19 @@ void CheckOther::checkEmptyStringTest()
         }
     }
 }
+//---------------------------------------------------------------------------
+// fflush(stdin) <- fflush only applies to output streams in ANSI C
+//---------------------------------------------------------------------------
+void CheckOther::checkFflushOnInputStream()
+{
+    for (const Token *tok = _tokenizer->tokens(); tok; tok = tok->next())
+    {
+        if (Token::Match(tok, "fflush ( stdin )"))
+        {
+            fflushOnInputStreamError(tok, tok->strAt(2));
+        }
+    }
+}
 
 //---------------------------------------------------------------------------
 // strtol(str, 0, radix)  <- radix must be 0 or 2-36
@@ -3502,3 +3515,9 @@ void CheckOther::emptyStringTestError(const Token *tok, const std::string &var_n
                     "emptyStringTest", "Non-empty string test can be simplified to \"*" + var_name + " != '\\0'\"");
     }
 }
+
+void CheckOther::fflushOnInputStreamError(const Token *tok, const std::string &varname)
+{
+    reportError(tok, Severity::possibleError,
+        "fflushOnInputStream", "fflush() called on input stream \"" + varname + "\" may result in undefined behaviour");
+}

lib/checkother.h

@@ -77,6 +77,7 @@ public:
         checkOther.invalidFunctionUsage();
         checkOther.checkZeroDivision();
         checkOther.checkMathFunctions();
+        checkOther.checkFflushOnInputStream();
 
         // New type of check: Check execution paths
         checkOther.executionPaths();
@@ -158,6 +159,9 @@ public:
     /** @brief %Check for inefficient empty string test*/
     void checkEmptyStringTest();
 
+    /** @brief %Check for using fflush() on an input stream*/
+    void checkFflushOnInputStream();
+
     // Error messages..
     void cstyleCastError(const Token *tok);
     void redundantIfDelete0Error(const Token *tok);
@@ -184,6 +188,7 @@ public:
     void mathfunctionCallError(const Token *tok, const unsigned int numParam = 1);
     void postIncrementError(const Token *tok, const std::string &var_name, const bool isIncrement);
     void emptyStringTestError(const Token *tok, const std::string &var_name, const bool isTestForEmpty);
+    void fflushOnInputStreamError(const Token *tok, const std::string &varname);
 
     void getErrorMessages()
     {
@@ -196,6 +201,7 @@ public:
         uninitvarError(0, "varname");
         zerodivError(0);
         mathfunctionCallError(0);
+        fflushOnInputStreamError(0, "stdin");
 
         // style
         cstyleCastError(0);
@@ -232,6 +238,9 @@ public:
                "* null pointer dereferencing\n"
                "* using uninitialized variables and data\n"
 
+               // possible error
+               "* using fflush() on an input stream\n"
+
                // style
                "* C-style pointer cast in cpp file\n"
                "* redundant if\n"
@@ -246,7 +255,8 @@ public:
                "* unusal pointer arithmetic. For example: \"abc\" + 'd'\n"
 
                // optimisations
-               "* optimisation: detect post increment/decrement\n";
+               "* optimisation: detect post increment/decrement\n"
+               "* optimisation: simplify empty string tests\n";
     }
 
 private:

test/testother.cpp

@@ -92,6 +92,8 @@ private:
         TEST_CASE(mathfunctionCall1);
 
         TEST_CASE(emptyStringTest);
+
+        TEST_CASE(fflushOnInputStreamTest);
     }
 
     void check(const char code[])
@@ -115,6 +117,7 @@ private:
         checkOther.checkZeroDivision();
         checkOther.checkMathFunctions();
         checkOther.checkEmptyStringTest();
+        checkOther.checkFflushOnInputStream();
     }
 
 
@@ -2471,6 +2474,21 @@ private:
         check("if (0 < strlen(str)) { }");
         ASSERT_EQUALS("[test.cpp:1]: (possible style) Non-empty string test can be simplified to \"*str != '\\0'\"\n", errout.str());
     }
+
+    void fflushOnInputStreamTest()
+    {
+        check("void foo()\n"
+              "{\n"
+              "    fflush(stdin);\n"
+              "}\n");
+        ASSERT_EQUALS("[test.cpp:3]: (possible error) fflush() called on input stream \"stdin\" may result in undefined behaviour\n", errout.str());
+
+        check("void foo()\n"
+              "{\n"
+              "    fflush(stdout);\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
+    }
 };
 
 REGISTER_TEST(TestOther)