Pointer

1,

Short int I;
Char;
Short int * pi;

I = 50;
Pi = & I;

---------------- Pointer, strong factory

Short int ** ppi; // This is a pointer to the pointer. Note that there are two * numbers.
Ppi = & pi;

 

------

Result:

The ppi is the IP address of pi.

* The ppi is the content in the pi address value, that is, the I address value. * Ppi (equivalent to pi, with the previous statement "ppi = & pi;" added "*" before, double negation)

** Ppi is the content of I. (Because * ppi = pi, ** ppi = * pi = I)

2. Example 2:

# Include "stdio. h" void find1 (char array [], char search, char * pa) {int I; for (I = 0; * (array + I )! = 0; I ++) {if (* (array + I) = search) {pa = array + I; break;} else if (* (array + I) = 0) {pa = 0; break ;}} int main () {char str [] = {"afsdfsdfdf \ 0 "}; // the string char a = 'd; // you can specify the char * p = 0 character; // if found, the pointer p points to the address of the first character found in the string. Find1 (str, a, p); // call a function to perform the operation. If (0 = p) {printf ("Not Found") ;}else {printf ("found, p = % d", p );}}

 

What do you think is the output of the above code?
Run it.
Alas! The output is: not found!
Instead of: found ,.......
Clearly, the value is 'd', and the fourth character of the str string is 'd'. You can find it!
Let's look at the function definition: void find1 (char [] array, char search, char * pa)
Check the call: find1 (str, a, p );
According to the analysis method in Article 5, an implicit value assignment operation is performed on each parameter during function calling.
The entire call is as follows:
Array = str;
Search =;
Pa = p; // note that the preceding three statements are the action implied during the call. // In my summary, see the function interface section: Exchg2 (int * px, int * py). Note that both the px and py parameters are pointers.
// Check the call position again: Exchg2 (& a, & B) int I; equivalent to px = & a; py = & B;
// It substitutes the address of a (& a) into px, and the address of B (& B) into py. Like the above value transfer, two implicit operations are performed during the function call: The & a, & B values are assigned to px, py.
For (I = 0; * (array + I )! = 0; I ++)
   {
If (* (array + I) = search)
      {
Pa = array + I
Break;
      }
Else if (* (array + I) = 0)
      {
Pa = 0;
Break;
      }
   }
Oh! There is no difference between the parameter pa and the parameter search. It is a value transfer (note: Address transfer is actually an address value transfer )! Therefore, changing the pa value (of course an address value) does not change the p value of the real variable, therefore, the value of p is not changed (that is, the point of p is not changed ).
(If you have any questions, take a look at Article 5: passing function parameters .)

Revised version:

# Include "stdio. h" void find1 (char array [], char search, char ** pa) {int I; for (I = 0; * (array + I )! = 0; I ++) {if (* (array + I) = search) {* pa = array + I; break;} else if (* (array + I) = 0) {* pa = 0; break ;}} int main () {char str [] = {"afsdfsdfdf \ 0 "}; // the string char a = 'd; // you can specify the char * p = 0 character; // if found, the pointer p points to the address of the first character found in the string. Find1 (str, a, & p); // call a function to perform the operation. If (0 = p) {printf ("Not Found");} else {printf ("found, p = % d", * p );}}

 

Complete analysis version:

# Include "stdio. h "void find1 (char array [], char search, char * pa) {int I; // note that not * pa = & p; but pa = & p, * pa = p. // If the preceding parameter is * pa, then pa = p is only a copy of p. pa is the content of p, so * pa points to the address where the content is used, the content is unknown. for (I = 0; * (array + I )! = 0; I ++) {if (* (array + I) = search) {* pa = array + I; break;} else if (* (array + I) = 0) {* pa = 0; break ;}} int main () {char str [] = {"afsdfsdfdf \ 0 "}; // the string char a = 'd; // you can specify the char * p = 0 character; // if found, the pointer p points to the address of the first character found in the string. Find1 (str, a, & p); // call a function to perform the operation. If (0 = p) {printf ("Not Found");} else {printf ("found, p = % d", * p );}}

 

Reference: http://blog.pfan.cn/whyhappy/5790.html

Pointer