Learning notes-const pointer, const int * P, int * const P, int const * P

 

# Include <iostream>
Using namespace STD;
Int main ()
{

Int int1 = 1;
Int int2 = 0;
Const int * pint1 = & int1;
Int * const pint2 = & int2;
Cout <"* pint1 =" <* pint1 <Endl;
Cout <"* pint2 =" <* pint2 <Endl;
* Pint1 = 2;
Pint2 = & int1;
Cout <"* pint1 =" <* pint1 <Endl;
Cout <"* pint2 =" <* pint2 <Endl;

Int N; // to prevent the screen from flashing
Cin> N;
Return 0;
}

The following error will pop up during this operation:

1> ------ generated: Project: vs2008, configuration: Debug Win32 ------
1> compiling...
1> main. cpp
1> G: \ learning \ vs2008project \ vs2008 \ vs2008 \ main. cpp (12): Error c3892: "pint1": cannot assign a value to a constant
1> G: \ learning \ vs2008project \ vs2008 \ vs2008 \ main. cpp (13): Error c3892: "pint2": cannot assign a value to a constant
1> the generated logs are stored in "file: // G: \ \ vs2008project \ vs2008 \ vs2008 \ debug \ buildlog.htm"
1> vs2008-2 errors, 0 warnings
============ Generate: 0 successful, 1 failed, 0 latest, skipped 0 ==========

Here we will illustrate

Pint1 is a pointer to an integer variable. The value it points to cannot be changed, that is, * pint1 cannot be modified, and pint1 can be changed to the address pointed to. That is, pint1 can be modified.

Pint2 is a constant pointer to an integer. the pointer is a constant, that is, the address pointed to by the pointer cannot be changed, that is, the value of pint2 cannot be changed, but * pint2 can be modified.

This is understandable.

For the definition of pint1, the right side of const is int, so the value that pint1 points to is a constant

For the definition of pint2, the right side of const is a variable, so this variable is a constant. What is this variable? After reading the complete definition, it is a pointer, so this is a pointer constant.

Next let's take a look.

Int const * P

# Include <iostream>
Using namespace STD;
Int main ()
{

Int int1 = 1;
Int int2 = 0;
Const int * pint1 = & int1;
Int * const pint2 = & int2;
Cout <"* pint1 =" <* pint1 <Endl;
Cout <"* pint2 =" <* pint2 <Endl;
* Pint1 = 2; // The number of rows is 12th.
Pint2 = & int1; // 13th rows
Cout <"* pint1 =" <* pint1 <Endl;
Cout <"* pint2 =" <* pint2 <Endl;
Int const * pint3 = & int1;
* Pint3 = 2; // The number of rows is 17th.
Pint3 = & int1;
Cout <"* pint3 =" <* pint3 <Endl;
Int N; // to prevent the screen from flashing
Cin> N;
Return 0;
}

The pop-up error is as follows:

1> ------ generated: Project: vs2008, configuration: Debug Win32 ------
1> compiling...
1> main. cpp
1> G: \ learning \ vs2008project \ vs2008 \ vs2008 \ main. cpp (12): Error c3892: "pint1": cannot assign a value to a constant
1> G: \ learning \ vs2008project \ vs2008 \ vs2008 \ main. cpp (13): Error c3892: "pint2": cannot assign a value to a constant
1> G: \ learning \ vs2008project \ vs2008 \ vs2008 \ main. cpp (17): Error c3892: "pint3": cannot assign a value to a constant
1> the generated logs are stored in "file: // G: \ \ vs2008project \ vs2008 \ vs2008 \ debug \ buildlog.htm"
1> vs2008-3 errors, 0 warnings
============ Generate: 0 successful, 1 failed, 0 latest, skipped 0 ==========

This shows that
Int const * P and int * const P are consistent, so you only need to check what is on the right of const to determine

In int const * P, the right side of const is * P, so P is a pointer constant.

In int * const P, the right side of const is P, so this variable is a constant and this variable is a pointer, so this is also a pointer constant.

In const int * P, the right side of const is int, so this integer is a constant, so the value of this * P cannot be changed;

 

Thank you

Author: Lin yufei
Source: http://www.cnblogs.com/zhengyuhong/
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