Struct pointer in C Language

Struct pointer in C Language
1. pointer variable pointing to the struct:
In C language, "->" is a whole. It is used to point to a struct. Suppose we define a struct in the program and declare a pointer variable pointing to this struct, then we need to use a pointer to retrieve the data in the struct, we need to use the pointing operator "-> ".


Example:
Struct SunLL
{
Int;
Int B;
Int c;
};

Struct SunLL * p; // defines the struct pointer.
Struct SunLL A = {1, 2, 3}; // defines A SunLL type variable

Int x; // defines a variable x
P = & A; // point p to
X = p-> a; // equivalent to x = (* p). a (* p) indicates the struct variable pointed to by p.
// The meaning of this sentence is to take out the data item a in the struct pointed to by p and assign it to x
// Because p points to A, p-> a = A. a, that is, 1

2. pointer variable pointing to the struct array:
The pointer variable pointing to the struct can also point to the struct array and its elements.


If the program is as follows:
Struct SunLL * p, sun [3];
P = sun;
If the sun [0] address is assumed to be 1000, the pointer Variable p points to the first address of the structure array sun, because the size of (struct SunLL) value is 6, each struct element occupies 6 bytes of memory space. Therefore, p + 1 points to address 1006, and p + 2 points to address 1012.

When you use pointer variables to point to struct variables or arrays, pay attention to the operator priority. In C language, () []->. the four operators with the same priority have the highest priority, followed by "*" "+ +" "--" "&" operators with the same priority. For example, the expression ++ P-> a is equivalent to ++ (p->)

(++ P)-> a calculate ++ p first, p points to sun [1];
P ++-> a; the expression is equivalent to (p ++)->;
The expression p-> a ++ is equivalent to (p-> a) ++;

3. struct as function parameters and struct pointer as function parameters


Example 1
Struct st
{
Int;
Char B;
};

Fun (struct st bc)
{
Bc. a + = 5;
Bc. B = 'a ';
Printf (% d, % c, bc. a, bc. B );
}

Main ()
{
Struct st bl;
Bl. a = 3;
Bl. B = c;
Fun (bl );
Printf (% d, % c, bl. a, bl. B );
}

Running result: 8, A 3, c

Example 2:
Struct st
{
Int;
Char B;
};

Fun (struct st * bp)
{
Bp-> a + = 5;
Bp-> B = 'a ';
Printf (% d, % c, bc. a, bc. B );
}

Main ()
{
Struct st bl;
Bl. a = 3;
Bl. B = c;
Fun (& bl );
Printf (% d, % c, bl. a, bl. B );
}

Running result: 8, A 8,

Summary:
The struct variable is used as a function parameter to pass the real parameter value to the form parameter, which is a value. All parameters of the struct are passed to the parameter, but their values are not changed. When a pointer pointing to a struct variable is passed as a real parameter, the address of the struct variable is passed to the shape parameter, which is an address transfer that changes the member value of the actual struct variable.