C++ VS2013: overwriting default constructor not working [duplicate]

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Default constructor with empty brackets (9 answers)

Closed 8 years ago.

I have a weird problem in C++. Probably I am just doing something wrong, but I can't figure out, what. I am using Microsoft VS2013 if that is important.

I created a new class with two constructors:

class CtVolume{
public:     
    CtVolume();                                             
    CtVolume(std::string path);                             
...

The first one should overwrite the default constructor. This is the one that does not work as I expected. If I do something like:

CtVolume myVolume();

then I think this should call the default constructor that I defined and execute the code I implemented for it. But it doesn't. The code in my Constructor is not executed. What is even more puzzling is that I can't use the myVolume like an object afterwards. If I attempt to call one of the methods implemented in the class:

myVolume.reconstructVolume();

The compiler does not let me compile my code. It says:

Error 5 error C2228: left of '.reconstructVolume' must have class/struct/union

So as it seems, this way I can't create an object.

Now, if I create the object with the keyword 'new' instead, my constructor code is being executed and everything works as expected. Example:

CtVolume* myVolume = new CtVolume();
myVolume->reconstructVolume();

This works fine.

Now another thing: if I use the other constructor I defined, both ways of creating the object work equally good, meaning this example:

CtVolume myVolume("sourcefiles/data/skullPhantom");
myVolume.reconstructVolume();

compiles and works as expected.

Now I tried to find out what type of myVolume is in the different cases, by calling typeid(myVolume).name(). This returns the type class CtVolume __cdecl(void) in the case that I described, where it "doesn't work" and class CtVolume in the "working" case where I used the other constructor.

Now can anybody tell me, what the __cdecl(void) means and what I did wrong? What also puzzles me is that I think I did that a lot of times before and it always worked for me until now.

Thanks!

Answer 1

The line:

CtVolume myVolume();

is interpreted by the compiler as a function declaration. Take a look at most vexing parse.

Just do:

CtVolume myVolume;

The above code will call the default constructor appropriately.