Programming_Micro_Note_20161006.md

#Programming Micro Note 20161006

extern and static

Q:
What do they mean?
A:
extern
for function: means it's a declaration, not necassarily needed.
for variable: means it's a declaration, definition may be in other file.

static
for function: means the funtions is visible only in this file.
for variable: means this variable lives during the whole running time of the program.
Q: Why not Global Variable? A: Scope(where the variable is visible,) global variable pollutes too much.

Forward-declare with namespace

Source:
Why can't I forward-declare a class in a namespace like this?

Q:
I have compilation error with forward-declare.

// for a class "Car" in namespace "myspace"
class myspace::Car;

Visual C++: error C2653

A:
Do this way

namespace myspace{
    class Car;
}

C++ allows you to do so only when the class is declared already. Some people say it should be legal.

wchar_t

Q: What do you think of wchar_t ? A: NEVER USE IT whenever possible, unless some stupid APIs do it that way. wchat_t is implemented environment-dependently.