Pass value, reference and pointer

Pass value

C in , all Non array form The data arguments of are Value passing form , Value passing is when calling a function , Copy a copy of the arguments to the calling function , That is to say, the function operates Copy of arguments and Not the argument itself . In a subfunction , For passed parameters （ Formal parameters ） Changes made Can't Act on the original variable .

#include <stdio.h>
void test(int x, int y);
int main() {
    
	int a = 1, b = 2;
	test(a, b);// What is passed here is a,b Value , Next, in the subfunction test（） in , Yes x,y The operation of will not affect a,b Original value of 
	printf("%d %d", a, b);
}
void test(int x, int y) {
    
	int tem;
	tem = x;
	x = y;
	y = tem;
}

Next is the monitoring of variables , You can see , After executing the code ,x,y The values of are interchanged and become 2,1, however Original value a,b Still 1,2

The reference

quote and The original variables It's a thing , Just change a name
The reference In essence, it passes the original variable Address
After having the address , The operation of variables will directly modify the values existing in the place , That is, the operation of variables in sub functions will directly act on the original variables .

#include <stdio.h>
void test(int &x, int &y);
/*  The formal parameter of the subfunction has an address character , When a sub function is called , It will directly take the address of the passed parameters ,  Make later right x,y The operation of acts directly on the original variable  */
int main() {
    
	int a = 1, b = 2;

	test(a, b);
	printf("%d %d", a, b);

}
void test(int &x, int &y) {
    
	int tem;
	tem = *x;
	*x = *y;
	*y = tem;

}

The pointer

The essence of pointer passing is Pass value , But this value is the original variable Address .

#include <stdio.h>
void test(int *x, int *y);
int main() {
    
	int a = 1, b = 2;

	test(&a, &b);
	printf("%d %d", a, b);

}
void test(int *x, int *y) {
    
	int tem;
	tem = *x;
	*x = *y;
	*y = tem;

}

Monitor page

You can see x,y The value of is a binary number , On behalf of a and b Of Address , The curly braces in the back refer to the address value