# V598. Memory manipulation function is used to work with a class object containing a virtual table pointer. The result of such an operation may be unexpected.

The analyzer has detected that such low-level functions as 'memset', 'memcpy', 'memmove', 'memcmp', 'memchr' are used to handle a class object. It is inadmissible when a class contains a pointer to a virtual function table (vtable).

If a pointer to an object is passed as a destination to the 'memset', 'memcpy' or 'memmove' functions, they may corrupt the vtable. If a pointer is passed as a source to the 'memcpy' or 'memmove' functions, the result of such copying may be unpredictable. In the case of 'memcmp' or 'memchr' functions, comparing or searching in the presence of the vtable may also lead to unexpected results.

Consider the following code sample:

    class MyClass
    {
    public:
      MyClass();
      virtual ~MyClass();

    private:
      int A, B, C;
      char buf[100];
    };

    MyClass::MyClass()
    {
      memset(this, 0, sizeof(*this));
    }

Note that there is a virtual destructor in the class. It means that the class has a vtable. The programmer was too lazy to clear the class data members separately and used the 'memset' function for that purpose. It will corrupt the vtable, since the 'memset' function does not know anything about it.

This is the correct code:

    MyClass::MyClass() : A(0), B(0), C(0)
    {
      memset(buf, 0, sizeof(buf));
    }

Since C++11, you can rewrite the code as follows if you want to zeroize data members:

    class MyClass
    {
    public:
      MyClass() = default;
      virtual ~MyClass() = default;

    private:
      int A = {}, B = {}, C = {};
      char buf[100] = {};
    };

This diagnostic is classified as:

CWE-665 CERT-EXP62-CPP CERT-OOP57-CPP

You can look at examples of errors detected by the V598 diagnostic.