C ++ references

C ++ references

C ++ reference learning:

Generally, the first function of referencing is the alias of the referenced variable. (This variable can be directly operated );

 

Referenced statement:

Type + & + name (can be considered as a regular pointer)

Note: (1) & indicates the identifier;

(2)When declaring a reference, you must first initialize it;

　　　(3) You cannot create an array reference. Because an array is composed of several elements, you cannot create an array alias;

 

Referenced applications:

(Reference as a parameter)

int swap(int &a, int &b){    int t = a;    a = b;     b = t;} 

(Reference as a constant)

int main(){  int b = 100;  const int &a = b;  return 0;}

This makes the code robust and has other requirements;

 

(Reference as return value)

Type + & + function name

(1) to reference the returned function value. to define a function, add & before the function name &;

(2) The biggest benefit of returning a function value with a reference is that a copy of the returned value is not generated in the memory.

 

But when the function returns the stack variable,Cannot be the initial value of other references; (Because the stack variable will be released after the function is completed)

Int & fun () {return a; // when the local variable is released, the reference to the local variable will point to an unknown memory space} int main () {int & a = fun ();}
// This is incorrect

And cannot be left;

 

 

The function returns static or global variables: (both variables are placed in the global zone)

Can be referenced as other values, and can be used as the left and right values;

 

Write a code in the above situations:

// Return the static variable int & fun1 () {static int a = 1; return a ;}// return the local variable int & fun2 () {int a = 2; return a;} // The referenced int & fun3 (int & a) {return a;} int main () {int a = fun1 (); int & B = fun1 (); cout <"a =" <a <endl; cout <"B =" <B <endl ;}
/* The running result is:
A = 1;
B = 1;
*/

This is because the parameter is global;

 

Main () {int a = fun2 (); int & B = fun2 () ;}/ * The running result is 2 and-2 (negative number indicates that the point to memory is not clear )*/

This is because the reference is a local variable that points to an ambiguous memory zone when the 2nd semicolon ends;

 

Main (){
Int c = 10; int a = fun3 (c); int & B = fun3 (c);}/* The running result is a = 10; B = 10 ;*/

The reference at this time is because the internal program will not be released before it ends;