Search code examples
c++pointersdereference

Dereferencing NULL pointer warning when checking if char* is null or empty

So simply put, I am checking if two char* are either nullptr or empty through an if statement but I get a warning saying I am dereferencing a null pointer.

// mplate is a reference to a class
if ((mplate.m_plate != nullptr || mplate.m_plate[0] != '\0') || (plate != nullptr || plate[0] != '\0')) {
// Do something
}
else {
// do something else
}

So basically i'm trying to say in the if statement is if either mplate.mplate or plate is empty or nullptr do this otherwise do something else.

Severity    Code    Description Project File    Line    Suppression State
Warning C6011   Dereferencing NULL pointer 'make'.
Warning C6011   Dereferencing NULL pointer 'model'.
Warning C6011   Dereferencing NULL pointer 'mplate.m_plate'.
Warning C6011   Dereferencing NULL pointer 'plate'.
Warning C6011   Dereferencing NULL pointer 'plate'.
Solution

  • You are doing something like

    if (p != nullptr || *p)

    i.e. you are dereferencing only if the pointer is nullptr. This means you do nothing if the pointer is valid, or you dereference if it's invalid (which is UB).

    You need to do a logical and instead, like this

    if (p != nullptr && *p)

    i.e. only dereference if the pointer is not nullptr.