A detailed explanation of the use of C + + Boolean types and references

1. Boolean type

Boolean types in C + +

• C + + adds to the basic type of language systembool

• The desirable values in C + + areboolonlytrueandfalse

• Theoreticallybooloccupies a byte

Attention:

trueRepresents the truth value, which is represented internally by the compiler

falseRepresents a non-truth value, and the compiler internally uses the

In the C language:

Use integer values insteadboolof types, often0:flase, 1:true

C + + does type enhancement, adds a very rigorousbooltype,trueandfalseexists as a keyword.

In C + + Boolean types,booltypes havetrueonlyfalsetwo values, and the C + + compiler converts non-0 values totrue0 values tofalse.

bool b = 0;
printf ("b =% d \ n", b);
b ++;
printf ("b =% d \ n", b);
b = b-3;
printf ("b =% d \ n", b);
// Does the bool type support mathematical operations?

in fact, in the C + + language, the internal implementation of the Boolean type is implemented with a single byte integer, thebooltype supports mathematical operations, the compiler adjusts internally, not 0 is true,0 false

Code test:

#include <stdio.h>

int main (int argc, char * argv [])
{
     bool b = false;
     int a = b;
    
     printf ("sizeof (b) =% d \ n", sizeof (b));
     // sizeof (b) = 1, bool type takes one byte
     printf ("b =% d, a =% d \ n", b, a); 0
     // b = 0, a = 0
    
     b = 3; // b = 1
     a = b; // a = 1
    
     printf ("b =% d, a =% d \ n", b, a);
    
     b = -5; // b = 1
     a = b; // a = 1
    
     printf ("b =% d, a =% d \ n", b, a);
    
     a = 10; // a = 10
     b = a; // b = 1
    
     printf ("a =% d, b =% d \ n", a, b);
    
     a = 0; // a = 0
     b = a; // b = 0
    
     printf ("a =% d, b =% d \ n", a, b);
    
     return 0;
}

The Boolean type is the basic data type in C + +

• You can defineboola global variable of type

• boolconstants that can define types

• You can defineboola pointer to a type

• boolan array of types can be defined

  ......

2, trinocular operator

The three-mesh operator is upgraded in C + +

Consider whether the following code is correct, compiling the run test in C and C + + environments, respectively

int a = 1;
int b = 2;
(a <b? a: b) = 3;
printf ("a =% d, b =% d \ n", a, b);
// Report an error in C
// in C ++, the result a = 3

Trinocular operator

• The three-mesh operator in the C language returns the value of the variable

• cannot be used as a left value

• The three-mesh operator in C + + can directly return the variable itself

• Can be used as a right value or as an Lvalue

Attention:

If one of the values that the Trinocular operator may return is a constant value, it cannot be used as an lvalue

The trinocular operator can be used as an lvalue only if all of the possible returns are variables, and a constant variable cannot be used as an lvalue.

What is the significance of such an upgrade to the three-mesh operator in C + +?

When all the possible returns of the Trinocular operator are variables, the variable itself is returned , which leads to a new concept: reference

3. References

3.1 Variable Name

A variable is an alias for an actual contiguous storage space, in which a variable is used to request and name the storage space, and the storage space is available through the name of the variable.

Question: Can I have only one alias for a contiguous storage space?

3.2 References

References in C + +

• Added the concept of references in C + +

  int a = 4;
  int & b = a; // b is an alias for a
  b = 5; // operation b is operation a
  

• A reference can be considered an alias for a defined variable

• Syntax for referencing:Type& name = var;

Attention:

A generic reference must be initialized with a variable of the same type when defined.

• What does C + + do with the three-mesh operator?

  int a = 1;
  int b = 2;
  (a <b? a: b) = 3; // ok, returns a reference to a or b, which can be used as an lvalue
  (a <b? 1: b) = 4; // err, returns the value of 1 or b, cannot be used as an lvalue 

• When the possible return of the trinocular operator is a variable, a variable reference is returned

• When there are constants in the possible return of the trinocular operator, the value returned is

4. Summary

The

boolType is the new added base type for C + +

boolType values can be onlytrueandfalse

The three-mesh operator in

C + + can be used as an lvalue

A reference in

C + + can be used as an alias for a variable

Three the possible return of the mesh operator is a variable, the return is a reference