C-to-C + + upgrade

C + + More emphasis on language practicality

1. All variables can be defined when they need to be used

I

int 0 ;  for (int i=1; i<=3; i++) {         for (int j=1; j<= 3; J + +)                  {+ = i * j;                }           }    

2. Register keyword request compiler to store local variables in registers

-register keyword is still supported in C + +

-c++ compiler has its own optimization method

Cannot get the address of register variable in C language

Address of register variable can be obtained in C + +

Register keyword in C + +

When the C + + compiler discovers that the address of a register variable is required in a program, the register of the variable becomes invalid.

The early C language compiler does not optimize the code, so the register variable is a good complement

3, in the C language, it is legal to repeatedly define a global variable with the same name, and more than one global variable with the same name in C will eventually be linked to the same address space on the global data area.

In C + +, it is not allowed to define multiple global variables with the same name

4, the strengthening of the struct keyword

-C language struct defines a set of variables

-a struct-defined identifier is not a new type in the C language

Structs in-c++ are used to define a completely new type

5. What is the difference between void F () and void f (void)?

The type of claim that all identifiers in C + + must display

The default type in C is not legal in C + +

In the C language:

int F () represents a function that returns a value of int that accepts arbitrary arguments

F (void) indicates an parameterless function with a return value of int

In C + +

int f () and int f (void) have the same meaning

An parameterless function that represents a return value of int

C-to-C + + upgrade