Summary of key points of C + + review (i.)

C + + 's strengthening of language--type strengthening

1. Register keyword Enhancement

Register keyword requests the compiler to put the variable directly inside the register, fast.

The register-modified variable in the C language cannot take the address, and the address can be taken in C + +.

2. Variable Detection Enhancements

In C language, it is legal to repeatedly define multiple global variables with the same name, and in C + +, it is not allowed to define multiple global variables with the same name.

3. All variables and functions in C + + must have a type

In the C language

int f (); A function that represents a return value of int that accepts arbitrary arguments

int f (void); An parameterless function that represents a return value of int

In C + +

int f (); and int f (void) have the same meaning, all of which represent an argument function with a return value of int

4. Three Mesh operator Enhancements

Example:a< B? A:B) = 30;

Difference: The C language Returns the value of the variable, and the C + + language is the return variable itself

The three-mesh operator in the C language returns the value of the variable and cannot be used as an lvalue

The three-mesh operator in C + + can return directly to the variable itself, so it can appear anywhere in the program

Note: If one of the values returned by the three-mesh operator is a constant value, it cannot be used as an lvalue (a < b? 1:b) = 30;

How does the C language support features like C + +?

====> when the condition of an lvalue: to have memory space; C + + compilers help programmers take an address

1.const Qualifier Recognition

Function: Converts an object into a constant, read-only.

int main () {const int a;//1 1th 2nd meaning represents a constant shaping int const b;//2CONST int *c;//3 3rd C is a pointer to a constant number (the memory data pointed to cannot be modified, but can be modified by itself ) int * Const D; 4 4th D constant pointer (pointer variable cannot be modified, but it points to memory space can be modified) const int * Const E; 5 5th e A pointer to a constant shape (the pointer and the memory space it points to cannot be modified) return 0;

Example:

const int Bufsize=512;bufsize cannot be modified after initialization. 1) in C + +, the const symbol table principle: storage is a symbol table that is key Valuekey valuebufsize 512

2. How the C + + compiler handles Const constants: When a constant is declared, it is placed in a constant in the symbol table, and the value in the symbol table is replaced directly with the constant.

Conclusion: The difference between C language and const variable in C + +

The const variable in C is a read-only variable with its own storage space

Const constants in C + +

May allocate storage space, or may not allocate storage space

When the const constant is global and needs to be used in other files

When using the & operator to take the address of a const constant

2) const and #define异同之处

Same: Both can be used as constants

XOR: Const constants are handled by the compiler, providing type detection and scope checking, macro definitions handled by the preprocessor, and simple text substitution.

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