Equations of Structure Double Pointer

In this section, you are going to learn

What are the different ways of declarations ?

How to dervie equations ?

What are the Properties of Variable ?

What are the Properties of Expression ?

Topics in this section,

• Derive Equations for Double Pointer

• Step 1 : Understand different methods to declare Double Pointer

  • Declaration 1 : Structure x, Single Pointer p, Double Pointer q are declared and assigned in same line

  • Declaration 2 : Structure x, Single Pointer p, Double Pointer q are declared and assigned in separate lines

  • Declaration 3 : Structure x, Single Pointer p, Double Pointer q are declared in one line and assigned in another line

  • Table of Declarations for Double Pointer

• Step 2 : Split pointer declarations and assignments into separate lines

• Step 3 : Derive Equations

• Step 4 : Apply above equations to analyse C statements

• Table of Equations for Single Pointer

• Table of Equations for Double Pointer

• Properties of a variable

  • Property 1 : Type

  • Property 2 : sizeof()

  • Property 3 : Scope, Lifetime and Memory of a variable

• Properties of Expressions

  • Table of Expressions

  • Table of Size (for Expressions)

  • Table of Types (for Expressions)

  • Table of Address/Value (for Expression)

  • Table of Function Prototype (for Expression)

• Summary

1. Equations of Double Pointer

In this section, you are going to learn

• How to derive pointer equations for Double pointer ?

• How to apply these equations to understand C statements ?

Derive Equations for Double Pointer

You can derive equations looking at C declarations !

Step 1 : Understand different methods to declare Double Pointer

There are many methods in C, using which a Double pointer can be declared. See below

Declaration 1 : Structure x, Single Pointer p, Double Pointer q are declared and assigned in same line

#include <stdio.h>

struct ABC
{
        int a;
        int b;
        int c;
};

int main(void)
{
        struct ABC x = {.a = 1, .b = 2, .c = 3}, *p = &x, **q = &p;

        printf("x.a = %d\n", x.a);
        printf("x.b = %d\n", x.b);
        printf("x.c = %d\n", x.c);

        printf("(**q).a = %d\n", (**q).a);
        printf("(**q).b = %d\n", (**q).b);
        printf("(**q).c = %d\n", (**q).c);

        printf("(*q)[0].a = %d\n", (*q)[0].a);
        printf("(*q)[0].b = %d\n", (*q)[0].b);
        printf("(*q)[0].c = %d\n", (*q)[0].c);

        printf("(*q)->a = %d\n", (*q)->a);
        printf("(*q)->b = %d\n", (*q)->b);
        printf("(*q)->c = %d\n", (*q)->c);

        printf("q[0][0].a = %d\n", q[0][0].a);
        printf("q[0][0].b = %d\n", q[0][0].b);
        printf("q[0][0].c = %d\n", q[0][0].c);

        return 0;
}

• Output is as below

x.a = 1
x.b = 2
x.c = 3

(**q).a = 1
(**q).b = 2
(**q).c = 3

(*q)[0].a = 1
(*q)[0].b = 2
(*q)[0].c = 3

(*q)->a = 1
(*q)->b = 2
(*q)->c = 3

q[0][0].a = 1
q[0][0].b = 2
q[0][0].c = 3

In this example,

• x is a structure

• p is an single structure pointer

• q is an double structure pointer

• x, p, q are declared in one Single Line

• x, p, q are assigned in one Single Line

• x is assigned with value 10

• p is assigned with address of x

• q is assigned with address of p

Declaration 2 : Structure x, Single Pointer p, Double Pointer q are declared and assigned in separate lines

#include <stdio.h>

struct ABC
{
        int a;
        int b;
        int c;
};

int main(void)
{
        struct ABC x = {.a = 1, .b = 2, .c = 3};
        struct ABC *p = &x;
        struct ABC **q = &p;

        printf("x.a = %d\n", x.a);
        printf("x.b = %d\n", x.b);
        printf("x.c = %d\n", x.c);

        printf("(**q).a = %d\n", (**q).a);
        printf("(**q).b = %d\n", (**q).b);
        printf("(**q).c = %d\n", (**q).c);

        printf("(*q)[0].a = %d\n", (*q)[0].a);
        printf("(*q)[0].b = %d\n", (*q)[0].b);
        printf("(*q)[0].c = %d\n", (*q)[0].c);

        printf("(*q)->a = %d\n", (*q)->a);
        printf("(*q)->b = %d\n", (*q)->b);
        printf("(*q)->c = %d\n", (*q)->c);

        printf("q[0][0].a = %d\n", q[0][0].a);
        printf("q[0][0].b = %d\n", q[0][0].b);
        printf("q[0][0].c = %d\n", q[0][0].c);

        return 0;
}

• Output is as below

x.a = 1
x.b = 2
x.c = 3

(**q).a = 1
(**q).b = 2
(**q).c = 3

(*q)[0].a = 1
(*q)[0].b = 2
(*q)[0].c = 3

(*q)->a = 1
(*q)->b = 2
(*q)->c = 3

q[0][0].a = 1
q[0][0].b = 2
q[0][0].c = 3

In this example,

• x is a structure

• p is a single structure pointer

• q is a double structure pointer

• x is declared in a separate line

• p is declared in a separate line

• q is declared in a separate line

• x is assigned in the same line of declaration

• p is assigned in the same line of declaration

• q is assigned in the same line of declaration

• x is assigned with value 10

• p is assigned with address of x

• q is assigned with address of p

Declaration 3 : Structure x, Single Pointer p, Double Pointer q are declared in one line and assigned in another line

#include <stdio.h>

struct ABC
{
        int a;
        int b;
        int c;
};

int main(void)
{
        struct ABC x;
        struct ABC *p;
        struct ABC **q;

        x.a = 1;
        x.b = 2;
        x.c = 3;

        p = &x;

        q = &p;

        printf("x.a = %d\n", x.a);
        printf("x.b = %d\n", x.b);
        printf("x.c = %d\n", x.c);

        printf("(**q).a = %d\n", (**q).a);
        printf("(**q).b = %d\n", (**q).b);
        printf("(**q).c = %d\n", (**q).c);

        printf("(*q)[0].a = %d\n", (*q)[0].a);
        printf("(*q)[0].b = %d\n", (*q)[0].b);
        printf("(*q)[0].c = %d\n", (*q)[0].c);

        printf("(*q)->a = %d\n", (*q)->a);
        printf("(*q)->b = %d\n", (*q)->b);
        printf("(*q)->c = %d\n", (*q)->c);

        printf("q[0][0].a = %d\n", q[0][0].a);
        printf("q[0][0].b = %d\n", q[0][0].b);
        printf("q[0][0].c = %d\n", q[0][0].c);

        return 0;
}

• Output is as below

x.a = 1
x.b = 2
x.c = 3

(**q).a = 1
(**q).b = 2
(**q).c = 3

(*q)[0].a = 1
(*q)[0].b = 2
(*q)[0].c = 3

(*q)->a = 1
(*q)->b = 2
(*q)->c = 3

q[0][0].a = 1
q[0][0].b = 2
q[0][0].c = 3

In this example,

• x is a structure

• p is a single structure pointer

• q is a double structure pointer

• x is declared in a separate line

• p is declared in a separate line

• q is declared in a separate line

• x is assigned and is not part of declaration

• p is assigned and is not part of declaration

• q is assigned and is not part of declaration

• x is assigned with value 10

• p is assigned with address of x

• q is assigned with address of p

Table of Declarations for Double Pointer

Decl #	Declaration	Description
Decl 1	struct ABC x, *p = &x, **q = &p;	Structure x, Single Pointer p, Double Pointer q are declared and assigned in same line
Decl 2	struct ABC x; struct ABC *p = &x; struct ABC **q = &p;	Structure x, Single Pointer p, Double Pointer q are declared and assigned in separate lines
Decl 3	struct ABC x; struct ABC *p; struct ABC **q; x.a = 1; x.b = 2; x.c = 3; p = &x; q = &p;	Structure x, Single Pointer p, Double Pointer q are declared in one line and assigned in another line

Step 2 : Split pointer declarations and assignments into separate lines

• Whenever we see any of the above methods of declarations, we need to rewrite them such that, declarations and assignments are not in same line. Similar to Declaration 3

Step 3 : Derive Equations

Derive Equations of Single Pointer

• Equation 1 : Obtained from Step 2

p = &x;

• Equation 2 : Move & to the left of First Equation. It turns in to *

*p = x;

• Equation 3 : * and [0] can be used interchangeably. Hence *p and p[0] are one and the same !

p[0] = x;

• Equation 4 : From Equation 2, Equation 3, we can derive that x, *p, p[0] all are same !

*p = p[0] = x;

Derive Equations of Double Pointer

• Equation 5 : Obtained from Step 2

q = &p;

• Equation 6 : Move & to the left of First Equation. It turns in to *

*q = p;

• Equation 7 : * and [0] can be used interchangeably. Hence *q and q[0] are one and the same !

q[0] = p;

• Equation 8 : From Equation 6, Equation 7, we can derive that p, *q, q[0] all are same !

*q = q[0] = p;

• Equation 9 : From Equation 1, we know p = &x. Hence Replace p with &x in Equation 8

*q = q[0] = &x;

• Equation 10 : Move & to the left of Equation 9. It turns in to *

**q = *q[0] = x;

• Equation 11 : * and [0] can be used interchangeably

q[0][0] = x;

Table of Equations for Single Pointer

Equation #	Equation	Description
Equation 1	p = &x	Base condition
Equation 2	*p = x	From Equation 1, Move & from RHS to LHS to get * on LHS
Equation 3	p[0] = x	* and [0] can be used interchangeably. Hence *p and p[0] are synonyms
Equation 4	*p = p[0] = x	From Equation 2, 3 we can conclude *p, p[0], x are synonyms

Table of Equations for Double Pointer

Equation #	Equation	Description
Equation 5	q = &p	Base condition
Equation 6	*q = p	From Equation 5, Move & from RHS to LHS to get * on LHS
Equation 7	q[0] = p	* and [0] can be used interchangeably. Hence *q and q[0] are synonyms
Equation 8	*q = q[0] = p	From Equation 6, Equation 7, we can derive that p, *q, q[0] all are same !
Equation 9	*q = q[0] = &x	From Equation 1, we know p = &x. Hence Replace p with &x in Equation 8
Equation 10	**q = *q[0] = x	From Equation 9, Move & from RHS to LHS to get * on LHS
Equation 11	q[0][0] = x	* and [0] can be used interchangeably

Step 4 : Apply above equations to analyse C statements

Example 1 : See Equation 2 : Changing *p changes the value of x

(*p).a = 10;
(*p).b = 20;
(*p).c = 30;

printf("(*p).a = %d\n", (*p).a);
printf("(*p).b = %d\n", (*p).b);
printf("(*p).c = %d\n", (*p).c);

Output is as below

(*p).a = 10
(*p).b = 20
(*p).c = 30

Example 2 : See Equation 3 : Changing p[0] changes the value of x

p[0].a = 10;
p[0].b = 20;
p[0].c = 30;

printf("p[0].a = %d\n", p[0].a);
printf("p[0].b = %d\n", p[0].b);
printf("p[0].c = %d\n", p[0].c);

Output is as below

p[0].a = 10
p[0].b = 20
p[0].c = 30

Example 3 : See Equation 4 : Changing x changes the value of *p and p[0]

x.a = 100;

printf("x.a = %d\n", x.a);
printf("(*p).a = %d\n", (*p).a);
printf("p[0].a = %d\n", p[0].a);
printf("p->a = %d\n", p->a);

Output is as below

x.a    = 100
(*p).a = 100
p[0].a = 100
p->a   = 100

Example 4 : Use “p->” notation of pointer to change contents of variable “x”

p->a = 10;
p->b = 20;
p->c = 30;

printf("p->a = %d\n", p->a);
printf("p->b = %d\n", p->b);
printf("p->c = %d\n", p->c);

Output is as below

p->a = 10
p->b = 20
p->c = 30

Example 5 : See Equation 10 : Changing **q changes the value of x

(**q).a = 100;

printf("x.a = %d, (**q).a = %d\n", x.a, (**q).a);

Output :

x.a = 100, (**q).a = 100

Example 6 : See Equation 10 : Changing *q[0] changes the value of x

(*q)[0].a = 100;

printf("x.a = %d, (*q)[0].a = %d\n", x.a, (*q)[0].a);

Output :

x.a = 100, (*q)[0].a = 100

Example 7 : See Equation 11 : Changing q[0][0] changes the value of x

q[0][0].a = 100;

printf("x.a = %d, q[0][0].a = %d\n", x.a, q[0][0].a);

Output :

x.a = 100, q[0][0].a = 100

Example 8 : See Equation 6 : *q, p are synonyms. Means chaning *q also changes p

struct ABC x, y, *p, **q;

x.a = 100;
p = &x;
q = &p;

printf("(*p).a = %d, p[0].a = %d, (**q).a = %d\n", (*p).a, p[0].a, (**q).a);

y.a = 200;

// *q, p are synonyms.
// Means *q = &y also means p = &y
*q = &y;

printf("(*p).a = %d, p[0].a = %d, (**q).a = %d\n", (*p).a, p[0].a, (**q).a);

Output :

(*p).a = 100, p[0].a = 100, (**q).a = 100

(*p).a = 200, p[0].a = 200, (**q).a = 200

Example 9 : See Equation 7 : q[0], p are synonyms. Means chaning q[0] also changes p

struct ABC x, y, *p, **q;

x.a = 100;
p = &x;
q = &p;

printf("(*p).a = %d, p[0].a = %d, (**q).a = %d\n", (*p).a, p[0].a, (**q).a);

y.a = 200;

// q[0], p are synonyms.
// Means q[0] = &y also means p = &y
q[0] = &y;

printf("(*p).a = %d, p[0].a = %d, (**q).a = %d\n", (*p).a, p[0].a, (**q).a);

Output :

(*p).a = 100, p[0].a = 100, (**q).a = 100

(*p).a = 200, p[0].a = 200, (**q).a = 200

Step 5 : Complete program

#include <stdio.h>

struct ABC
{
        int a;
        int b;
        int c;
};

int main(void)
{
        struct ABC x;

        struct ABC *p;

        struct ABC **q;

        x.a = 10;

        p = &x;

        q = &p;

        printf("x.a = %d, (*p).a = %d, p[0].a = %d, (**q).a = %d\n", x.a, (*p).a, p[0].a, (**q).a);

        x.a = 20;

        printf("x.a = %d, (*p).a = %d, p[0].a = %d, (**q).a = %d\n", x.a, (*p).a, p[0].a, (**q).a);

        (*p).a = 30;

        printf("x.a = %d, (*p).a = %d, p[0].a = %d, (**q).a = %d\n", x.a, (*p).a, p[0].a, (**q).a);

        p[0].a = 40;

        printf("x.a = %d, (*p).a = %d, p[0].a = %d, (**q).a = %d\n", x.a, (*p).a, p[0].a, (**q).a);

        (**q).a = 50;
        printf("x.a = %d, (*p).a = %d, p[0].a = %d, (**q).a = %d\n", x.a, (*p).a, p[0].a, (**q).a);

        return 0;
}

• Output is as below

x.a = 10, (*p).a = 10, p[0].a = 10, (**q).a = 10

x.a = 20, (*p).a = 20, p[0].a = 20, (**q).a = 20

x.a = 30, (*p).a = 30, p[0].a = 30, (**q).a = 30

x.a = 40, (*p).a = 40, p[0].a = 40, (**q).a = 40

x.a = 50, (*p).a = 50, p[0].a = 50, (**q).a = 50

2. Properties of a variable

Properties of a variable

In this section, you are going to learn

• Properties of a variable

  • Type of a variable ?

  • Size of a variable ?

  • Scope, Lifetime and Memory of a variable ?

Property 1 : Type

Property 1.1 : type_of(variable)

struct ABC x;

struct ABC *p;

struct ABC **q;

p = &x;

q = &p;

• In above code snippet, there are three variables x, p, q

Variable	Type	Description
type_of(x)	struct ABC	See Line 1
type_of(p)	struct ABC *	See Line 3
type_of(q)	struct ABC **	See Line 5

Property 1.2 : type_of(&variable)

Adress of variable must be stored in next level pointer type always

struct ABC x;

struct ABC *p;

struct ABC **q;

p = &x;

q = &p;

• In above code snippet, there are two variables x, p

Variable	Type	Description
type_of(&x)	struct ABC *	type_of(x) is struct ABC Hence, type_of(&x) is struct ABC *
type_of(&p)	struct ABC **	type_of(p) is struct ABC * Hence, type_of(&p) is struct ABC **
type_of(&q)	struct ABC ***	type_of(q) is struct ABC ** Hence, type_of(&q) is struct ABC ***

Property 2 : sizeof()

Property 2.1 : sizeof() of basic types

Sizeof(type)	Size
sizeof(char)	1 Byte
sizeof(int)	4 Bytes
sizeof(float)	4 Bytes
sizeof(double)	8 Bytes

Property 2.2 : sizeof() of pointer types

sizeof(pointer types) is always 8 Bytes, where pointer is single, double, triple etc.,:

Sizeof(type *)	Size
sizeof(char *)	8 Bytes
sizeof(int *)	8 Bytes
sizeof(float *)	8 Bytes
sizeof(double *)	8 Bytes
sizeof(struct xyz *)	8 Bytes
sizeof(union xyz *)	8 Bytes

Sizeof(type **)	Size
sizeof(char **)	8 Bytes
sizeof(int **)	8 Bytes
sizeof(float **)	8 Bytes
sizeof(double **)	8 Bytes
sizeof(struct xyz **)	8 Bytes
sizeof(union xyz **)	8 Bytes
etc.,

Property 2.3 : sizeof(&variable) - sizeof address of variable

sizeof(&variable) is always 8 Bytes, where type_of(variable) can be anything

Sizeof(&variable)	Size	Declaration
sizeof(&x)	8 Bytes	char x;
sizeof(&x)	8 Bytes	int x;
sizeof(&x)	8 Bytes	float x;
sizeof(&x)	8 Bytes	double x;
sizeof(&x)	8 Bytes	struct xyz x;
sizeof(&x)	8 Bytes	union xyz x;

Sizeof(&variable)	Size	Declaration
sizeof(&x)	8 Bytes	char *x;
sizeof(&x)	8 Bytes	int *x;
sizeof(&x)	8 Bytes	float *x;
sizeof(&x)	8 Bytes	double *x;
sizeof(&x)	8 Bytes	struct xyz *x;
sizeof(&x)	8 Bytes	union xyz *x;

Sizeof(&variable)	Size	Declaration
sizeof(&x)	8 Bytes	char **x;
sizeof(&x)	8 Bytes	int **x;
sizeof(&x)	8 Bytes	float **x;
sizeof(&x)	8 Bytes	double **x;
sizeof(&x)	8 Bytes	struct xyz **x;
sizeof(&x)	8 Bytes	union xyz **x;

Property 2.4 : sizeof() of variable

sizeof(variable) equals sizeof(typeof(variable))

struct ABC x;

struct ABC *p;

struct ABC **q;

p = &x;

q = &p;

• In above code snippet, there are three variables x, p, q

Sizeof(Variable)	Size	Description
sizeof(x)	12 Bytes	How ? Step 1 : sizeof(x) equals sizeof(typeof(x)) Step 2 : type_of(x) is struct ABC Step 3 : sizeof(struct ABC) is 12 Bytes Hence, sizeof(x) is 12 Bytes
sizeof(p)	8 Bytes	How ? Step 1 : sizeof(p) equals sizeof(typeof(p)) Step 2 : type_of(p) is struct ABC * Step 3 : sizeof(struct ABC *) is 8 Bytes Hence, sizeof(p) is 8 Bytes
sizeof(q)	8 Bytes	How ? Step 1 : sizeof(q) equals sizeof(typeof(q)) Step 2 : type_of(q) is struct ABC ** Step 3 : sizeof(struct ABC **) is 8 Bytes Hence, sizeof(q) is 8 Bytes

Property 3 : Scope, Lifetime and Memory of a variable

• Global Scope and Lifetime.

• Local Scope and Lifetime

3. Properties of Expressions

In this section, you are going to learn

• Properties of Expressions

  • What is an Expression ?

  • Table of Expressions

  • Table of Size (for Expressions)

  • Table of Type (for Expressions)

  • Table of Address/Value (for Expression)

  • Table of Function Prototype (for Expression)

Properties of Expressions

Let us write-down expression tables for below code snippet

struct ABC x;

struct ABC *p;

struct ABC **q;

p = &x;

q = &p;

(*p).a = 100;    // or p->a = 100;

(**q).a = 100;   // or (*q)->a = 100;

Table of Expressions

Expression	Description
x	x is a structure
&x	&x is address of a structure &x is a single pointer
p	p is a pointer to a structure p is a single pointer
&p	&p is address of a pointer &p is a double pointer
*p	*p is a structure, because *p = x. See Equation 2
p[0]	p[0] is a structure, because p[0] = x. See Equation 3
q	q is a double pointer and holds the address of a single pointer
&q	&q is address of a double pointer &q is a triple pointer
*q	*q holds the address of structure x. See Equation 9 *q is a single pointer. *q = p. See Equation 8
q[0]	q[0] holds the address of structure x. See Equation 9 q[0] is a single pointer. *q = p. See Equation 8
**q	**q is a structure. See Equation 10
*q[0]	*q[0] is a structure. See Equation 10
q[0][0]	q[0][0] is a structure. See Equation 11

Table of Size (for Expressions)

Expression	Size	Description
sizeof(x)	12 Bytes	See Property 2.4
sizeof(&x)	8 Bytes	See Property 2.3
sizeof(p)	8 Bytes	See Property 2.4
sizeof(&p)	8 Bytes	See Property 2.3
sizeof(*p)	12 Bytes	Step 1 : sizeof(*p) equals sizeof(x) See Equation 2 Step 2 : sizeof(x) equals sizeof(type_of(x)) See Property 2.4 Step 3 : sizeof(type_of(x)) equals sizeof(struct ABC) See Property 1.1 Step 4 : sizeof(struct ABC) equals 12 Bytes
sizeof(p[0])	12 Bytes	Step 1 : sizeof(p[0]) equals sizeof(x)``= x See Equation 3 Step 2 : sizeof(x) equals sizeof(type_of(x)) See Property 2.4 Step 3 : sizeof(type_of(x)) equals sizeof(struct ABC) See Property 1.1 Step 4 : sizeof(struct ABC) equals 12 Bytes
sizeof(q)	8 Bytes	See Property 2.4
sizeof(&q)	8 Bytes	See Property 2.3
sizeof(*q)	8 Bytes	Step 1 : sizeof(*q) equals sizeof(p). See Equation 8 Step 2 : sizeof(p), equals sizeof(type_of(p)) See Property 2.4 Step 3 : sizeof(type_of(p)) equals sizeof(struct ABC *) See Property 1.1 Step 4 : sizeof(struct ABC *) equals 8 Bytes
sizeof(q[0])	8 Bytes	Step 1 : sizeof(q[0]) equals sizeof(p) See Equation 8 Step 2 : sizeof(p) equals sizeof(type_of(p)) See Property 2.4 Step 3 : sizeof(type_of(p)) equals sizeof(struct ABC *) See Property 1.1 Step 4 : sizeof(struct ABC *) * equals 8 Bytes
sizeof(**q)	12 Bytes	Step 1 : sizeof(**q) equals sizeof(x) See Equation 10 Step 2 : sizeof(x) equals sizeof(type_of(x)) See Property 2.4 Step 3 : sizeof(type_of(x)) equals sizeof(struct ABC) See Property 1.1 Step 4 : sizeof(struct ABC) equals 12 Bytes
sizeof(*q[0])	12 Bytes	Step 1 : sizeof(*q[0]) equals sizeof(x) See Equation 10 Step 2 : sizeof(x) equals sizeof(type_of(x)) See Property 2.4 Step 3 : sizeof(type_of(x)) equals sizeof(struct ABC) See Property 1.1 Step 4 : sizeof(struct ABC) equals 12 Bytes
sizeof(q[0][0])	12 Bytes	Step 1 : sizeof(q[0][0]) equals sizeof(x) See Equation 11 Step 2 : sizeof(x) equals sizeof(type_of(x)) See Property 2.4 Step 3 : sizeof(type_of(x)) equals sizeof(struct ABC) See Property 1.1 Step 4 : sizeof(struct ABC) equals 12 Bytes

Table of Types (for Expressions)

Expression	Type	Description
type_of(x)	struct ABC	See Property 1.1
type_of(&x)	struct ABC *	See Property 1.2
type_of(p)	struct ABC *	See Property 1.1
type_of(&p)	struct ABC **	See Property 1.2
type_of(*p)	struct ABC	Step 1 : type_of(*p) equals type_of(x), because *p = x. See Equation 2 Step 2 : type_of(x) equals struct ABC
type_of(p[0])	struct ABC	Step 1 : type_of(p[0]) equals type_of(x), because p[0] = x. See Equation 3 Step 2 : type_of(x) equals struct ABC
type_of(q)	struct ABC **	See Property 1.1
type_of(&q)	struct ABC ***	See Property 1.2
type_of(*q)	struct ABC *	Step 1 : type_of(*q) equals type_of(p). See Equation 8 Step 2 : type_of(p), equals struct ABC * See Property 1.1
type_of(q[0])	struct ABC *	Step 1 : type_of(q[0]) equals type_of(p) See Equation 8 Step 2 : type_of(p) equals struct ABC * See Property 1.1
type_of(**q)	struct ABC	Step 1 : type_of(**q) equals type_of(x) See Equation 10 Step 2 : type_of(x) equals struct ABC See Property 1.1
type_of(*q[0])	struct ABC	Step 1 : type_of(*q[0]) equals type_of(x) See Equation 10 Step 2 : type_of(x) equals struct ABC See Property 1.1
type_of(q[0][0])	struct ABC	Step 1 : type_of(q[0][0]) equals type_of(x) See Equation 11 Step 2 : type_of(x) equals struct ABC See Property 1.1

Table of Address/Value (for Expression)

Expression	Address/Value	Description
x	Value	Step 1 : x is a structure Step 2 : Hence x is a value
&x	Address	& operator indicates address
p	Address	Step 1 : p = &x See Equation 1 Step 2 : & operator indicates address
&p	Address	& operator indicates address
*p	Value	Step 1 : *p is a structure. *p = x See Equation 2 Step 2 : Hence *p is a value
p[0]	Value	Step 1 : p[0] is a structure. p[0] = x See Equation 3 Step 2 : Hence p[0] is a value
q	Address	Step 1 : q = &p See Equation 5 Step 2 : & operator indicates address
&q	Address	& operator indicates address
*q	Address	Step 1 : *q = p See Equation 6 Step 2 : p = &x Step 3 : & operator indicates address
q[0]	Address	Step 1 : q[0] = p See Equation 7 Step 2 : p = &x Step 3 : & operator indicates address
**q	Value	Step 1 : **q = x See Equation 10 Step 2 : x is a structure Step 3 : **q is a Value
*q[0]	Value	Step 1 : *q[0] = x See Equation 10 Step 2 : x is a structure Step 3 : *q[0] is a Value
q[0][0]	Value	Step 1 : q[0][0] = x See Equation 11 Step 2 : x is a structure Step 3 : q[0][0] is a Value

Table of Function Prototype (for Expression)

If fun(v) is function call then, fun(type_of(v)) is the prototype

Function call	Function Prototype	Description
fun(x)	void fun(struct ABC x);	See Property 1.1
fun(&x)	void fun(struct ABC *p);	See Property 1.2
fun(p)	void fun(struct ABC *p);	See Property 1.1
fun(&p)	void fun(struct ABC **p);	See Property 1.2
fun(*p)	void fun(struct ABC x);	Step 1 : fun(*p) equals fun(x)See Equation 2 Step 2 : fun(x) equals fun(type_of(x)) Step 3 : fun(type_of(x)) equals fun(struct ABC)
fun(p[0])	void fun(struct ABC x);	Step 1 : fun(p[0]) equals fun(x)See Equation 2 Step 2 : fun(x) equals fun(type_of(x)) Step 3 : fun(type_of(x)) equals fun(struct ABC)
fun(q)	void fun(struct ABC **q);	See Property 1.1
fun(&q)	void fun(struct ABC ***q);	See Property 1.2
fun(*q)	void fun(struct ABC *q);	Step 1 : fun(*q) equals fun(p) Step 2 : fun(p) equals fun(type_of(p)) Step 3 : fun(type_of(p)) equals fun(struct ABC *)
fun(q[0])	void fun(struct ABC *q);	Step 1 : fun(q[0]) equals fun(p) Step 2 : fun(p) equals fun(type_of(p)) Step 3 : fun(type_of(p)) equals fun(struct ABC *)
fun(**q)	void fun(struct ABC x);	Step 1 : fun(**q) equals fun(x) See Equation 10 Step 2 : fun(x) equals fun(type_of(x)) Step 3 : fun(type_of(x)) equals fun(struct ABC)
fun(*q[0])	void fun(struct ABC x);	Step 1 : fun(*q[0]) equals fun(x) See Equation 10 Step 2 : fun(x) equals fun(type_of(x)) Step 3 : fun(type_of(x)) equals fun(struct ABC)
fun(q[0][0])	void fun(struct ABC x);	Step 1 : fun(q[0][0]) equals fun(x) See Equation 11 Step 2 : fun(x) equals fun(type_of(x)) Step 3 : fun(type_of(x)) equals fun(struct ABC)

4. Summary

#	?	Size in Bytes	Type	Address or Value	Function call	Function Prototype
x	Structure	12	struct ABC	Value	fun(x)	void fun(struct ABC x);
&x	Single Pointer	8	struct ABC *	Address	fun(&x)	void fun(struct ABC *p);
p	Single Pointer	8	struct ABC *	Address	fun(p)	void fun(struct ABC *p);
&p	Double Pointer	8	struct ABC **	Address	fun(&p)	void fun(struct ABC **q);
*p	Structure	12	struct ABC	Value	fun(*p)	void fun(struct ABC x);
p[0]	Structure	12	struct ABC	Value	fun(p[0])	void fun(struct ABC x);
q	Double Pointer	8	struct ABC **	Address	fun(q)	void fun(struct ABC **q);
&q	Triple Pointer	8	struct ABC ***	Address	fun(&q)	void fun(struct ABC ***r);
*q	Single Pointer	8	struct ABC *	Address	fun(*q)	void fun(struct ABC *p);
q[0]	Single Pointer	8	struct ABC *	Address	fun(q[0])	void fun(struct ABC *p);
**q	Structure	12	struct ABC	Value	fun(**q)	void fun(struct ABC x);
*q[0]	Structure	12	struct ABC	Value	fun(*q[0])	void fun(struct ABC x);
q[0][0]	Structure	12	struct ABC	Value	fun(q[0][0])	void fun(struct ABC x);

See Also

• Equations of Structure Single Pointer

• Equations of Structure Triple Pointer

See Also

• Current Module

  • Basic Equations

• Next Module

  • Basic Arrays

• Other Modules

  • Malloc and Pointers

  • Type-Casting and Pointers

  • Functions and Pointers

  • Memcpy and Pointers

  • Const Pointers

  • void Pointers

  • Array of Pointers

  • Pointer to an Array

  • Function Pointers

  • Pre Increment with Pointers

  • Post Increment with Pointers

  • Pre decrement with Pointers

  • Post Decrement with Pointers