Error: Member Access into Incomplete Type:Forward Declaration Of

error: member access into incomplete type : forward declaration of

Move doSomething definition outside of its class declaration and after B and also make add accessible to A by public-ing it or friend-ing it.

class B;

class A
{
    void doSomething(B * b);
};

class B
{
public:
    void add() {}
};

void A::doSomething(B * b)
{
    b->add();
}

Member access into incomplete type error

You're asking for a member in the FooEncoder struct which isn't visible anywhere in your foo_interface.cc file. This looks similar to a pimpl idiom.

In order to have your code aware of FooEncoder's structure you need to either

#include "foo_encoder.c"

in your foo_interface.cc file (I quite don't like this solution and you didn't post the full code either) or move your struct definition elsewhere in a header file and include that one (recommended).

error: member access into incomplete type''; note: forward declaration of ''

The definition of the constructor B::B inside the struct definition references members of MAIN, but the latter hasn't been fully defined yet.

You need to move the body of constructor B::B into a separate file, i.e. b.cpp, and link with main.cpp when building the executable.

Clang error: member access into incomplete type

It looks like you forward declare IdInterface at file scope. Looking at your linked github repo, IdInterface is defined in namespace src. src::IdInterface != ::IdInterface You have forward declared a type that is never defined.

Update your forward declaration to be in namespace src and it will likely fix your issue.

namespace src{
    class IdInterface;
}
namespace validator
{

class IdValidatorInterface : public virtual BaseElementValidatorInterface
    {

 public:
     IdValidatorInterface();
     virtual ~IdValidatorInterface();

     virtual bool isValid( shared_ptr<src::IdInterface> entity )  = 0;
     virtual vector<string> validate( shared_ptr<src::IdInterface> entity) = 0;

    };

}

c++ - error: member access into incomplete type in base class virtual function

This problem is known as circular dependency.

In your code..

// in shape.h

struct HitRecord;   // forward declaration

                    // this forward declaration means all you can do until 
                    // the struct is fully declared is declare a pointer
                    // or a reference to it.  No more.

class Shape {
public:
    virtual bool intersect(Ray& r, HitRecord& rec);  // <-- this is fine

    virtual bool intersect(Ray& r, HitRecord& rec) {
        //...
        rec.obj = this;   // <-- this is where you hit an error. the compiler
                          // doesn't know yet what HitRecord::obj is.
        return false;
    }
};

.. in hitrecord.h...

struct HitRecord {
    float t;
    vec3f p;    // point coord
    vec3f norm;
    Shape* obj;
};

 // this would usually reside in shape.cpp, but what's important is the order
 // in which the compiler reads the successive declarations

 #include "shape.h"
 #include "hitrecord.h"   // for example...

 bool Shape::intersect(Ray& r, HitRecord& rec) 
 {
 //...
     rec.obj = this;   // Now, the compiler knwos all about HitRecord
                       // so this will compile.
     return false;
 }

How to resolve Member access into incomplete type error

You have declared RootViewController as a forward class declaration in your .h file using the @Class directive, but you haven't imported RootViewController.h in your ADBanner.mm file.

This means that the compiler knows that there is some class RootViewController but doesn't know anything more about it - its superclass, methods or properties. As such it can't confirm that it actually has a method layoutIfNeeded.

Adding #import "RootViewController.h" to the top of ADBanner.mm will give the compiler the information it needs and resolve the error.

QT 5.13.2 C++ issue Member access into incomplete type 'Ui::UsersWidget'

1) ui should be a pointer

2) Name the ui object "UsersWidget", not "Form"

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