C language: structures and structure pointers-EEWORLD

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1. Pointer variable pointing to the structure:

In C language, -> is a whole, which is used to point to a structure. Suppose we define a structure in the program, and then declare a pointer variable to point to this structure. If we want to use the pointer to retrieve the data in the structure, we need to use the pointing operator "->".

for example:

struct SunLL

{

int a;

int b;

int c;

};

struct SunLL * p; //define structure pointer

struct SunLL A = {1,2,3}; //define a variable A of type SunLL

int x; //define a variable x

p = &A ; //Let p point to A

x = p->a; // equivalent to x=(*p).a (*p) indicates the structure variable pointed to by p

//This sentence means to take out the data item a contained in the structure pointed to by p and assign it to x

//Since p points to A at this time, p->a == Aa, which is 1

2. Pointer variable pointing to structure array:

A pointer variable pointing to a structure can also point to an array of structures and their elements.

If the procedure is as follows:

struct SunLL *p,sun[3];

p = sun;

If we assume that the address of sun[0] is 1000, the pointer variable p points to the first address of the structure array sun. Since the value of size of (struct SunLL) is 6, each structure element occupies 6 bytes of memory space, so p+1 points to address 1006, and p+2 points to address 1012.

When using pointer variables to point to structure variables or structure arrays, you should pay attention to the priority of operators. In C language, "()", "[ ]", "->", and "." have the same priority, which has the highest priority, followed by "*", "++", "--", and "&". For example, the expression ++P->a is equivalent to ++(p->a)

(++p)->a first calculates ++p, and p points to sun[1];

P++->a; then the expression is equivalent to (p++)->a;

The expression p->a++ is equivalent to (p->a)++;

3. Structure as function parameter and structure pointer as function parameter

Example 1

struct st

{

int a;

char b;

};

fun(struct st bc)

{

bc.a+=5;

bc.b='A';

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

}

main()

{

struct st bl;

bl.a=3;

bl.b="c";

fun(bl);

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

}

The result is: 8, A 3, c

Example 2:

struct st

{

int a;

char b;

};

fun（struct st *bp）

{

bp->a+=5;

bp->b='A';

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

}

main()

{

struct st bl;

bl.a=3;

bl.b="c";

fun(&bl);

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

}

The running result is: 8, A 8, A

Summarize:

When a structure variable is used as a function parameter, the actual parameter value is passed to the formal parameter, which is a value transfer. When all the parameters of the structure are passed to the formal parameter for use, the value of the structure itself will not change. When a pointer to a structure variable is passed as an actual parameter, the address of the structure variable is passed to the formal parameter, which is an address transfer and will change the member values of the actual structure variable.

Reference address：C language: structures and structure pointers

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