Creating A Typedef In C++ - c++

Question

What Searching I've Done:
Hello, so typedefs are a new topic to me, and I have already read a page about them. (http://en.cppreference.com/w/cpp/language/typedef) But that's the best information I could find, the only problem is because I have no idea how it's working enough, I'm unable to rework it and use it for my situation.
Also, for the heads up; I'm trying to create a type like the 'App' type that you write when creating a CLR Form in C++. (Visual Studio) The only difference is it will be used for a different reason, so don't copy the code from it please.
My Code:
#pragma once
class Application {
public:
typedef class App; // Runnable C++ object (TEST PLEASE DON'T JUDGE)
private:
void Run(App myApp) { // ERROR: incomplete type is not allowed
}
};
How You Can Help Me:
Explain what a typedef is used for. (Examples will work)
Explain in what type I should create the 'App' type. (Eg. Class, String, Int, etc.) Or explain in what other way I can do so.
You can also just create an example with comments explaining.
Thanks for the help! I tried to keep this question real explainable and sleek.

Answer 1

In C++, typedef simply creates an alias for another type, such that referencing the new type is identical to referencing the original type.
// create a alias for the int type
typedef int my_new_type;
// here a and b have the same type
int a = 1;
my_new_type b = 1;
The above is a contrived example, generally the types you use typedef for would be more complex (like std::vector<std::pair<int, std::string>>). For your use case, I'm not sure a typedef is what you are looking for.

Answer 2

I think you're looking for
typedef Application App;
But I'm not sure why you don't just do
class Application {
private:
void Run(Application myApp) {
}
};
As for usage, one use for typedef is to define types whose underlying type may vary depending on the build configuration, target platform and compiler. For example if you are writing a game that will run on PS4 and XBOX One, you might be using two different compilers depending on which platform you are building for.
#if defined(MSVC)
typedef __int64 TInt64;
#elif defined(GCC)
typedef int64_t TInt64;
#endif
This allows more of your code to be platform-agnostic and abstracts away compiler/platform details making app code more readable and encapsulating the assumptions we're interested in. It also reduces codebase size and preprocessing which can improve your compile times.
// We can assume this will be exactly 64 bits on all our target platforms.
TInt64 myInt = 0x1000000000000000;
P.S. Although it doesn't cover typedefs in general Marshall Cline's C++ FAQ is an great resource for beginners and experts alike.