[Review C] pointer

Recently, I took the time to re-read "data structure and algorithm (C language version)", and I felt a lot unfamiliar with the C language. So I took the time to review the C language and record it.

(The original image is edited by omnigraffle pro)

//// Main. C // practicec // created by viktyz on 13-6-8. // copyright (c) 2013 viktyz. all rights reserved. // # 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;/* breakpoint 2 */break; /* breakpoint 3 */} else if (* (array + I) = 0) {* pA = 0; break ;}} int main (INT argc, const char * argv []) {char STR [] = {"afsdfsdfdf \ 0"}; char a = 'D'; char * p = 0; find1 (STR,, & P);/* breakpoint 1 */If (0 = P)/* breakpoint 4 */{printf ("not found! \ N ");} else {printf (" found! \ N ") ;}return (0 );}

The above Code comes from the complete handling of the C pointer (full version: Revision of the supplemental version), with = Yao Yunfei revision = Ding Zhengyu.

It is mainly used to demonstrate pointer usage. in Mac OS 10.8 and xcode 4.6.2, the single-step debugging result is as follows:

Breakpoint 1:

(lldb) p *p(char) $0 = '\0'(lldb) p p(char *) $1 = 0x0000000000000000(lldb) p &p(char **) $2 = 0x00007fff5fbff880(lldb) p *str(char) $3 = 'a'(lldb) p str[0](char) $4 = 'a'(lldb) p &str[0](char *) $5 = 0x00007fff5fbff88c "afsdfsdfdf"(lldb) p str(char [12]) $6 = "afsdfsdfdf" {  (char) [0] = 'a'  (char) [1] = 'f'  (char) [2] = 's'  (char) [3] = 'd'  (char) [4] = 'f'  (char) [5] = 's'  (char) [6] = 'd'  (char) [7] = 'f'  (char) [8] = 'd'  (char) [9] = 'f'  (char) [10] = '\0'  (char) [11] = '\0'}(lldb) p &str(char (*)[12]) $7 = 0x00007fff5fbff88c(lldb) p str[3](char) $8 = 'd'(lldb) p &str[3](char *) $9 = 0x00007fff5fbff88f "dfsdfdf"

Breakpoint 2:

(lldb) p **pa(char) $10 = '\0'(lldb) p *pa(char *) $11 = 0x0000000000000000(lldb) p pa(char **) $12 = 0x00007fff5fbff880(lldb) p &pa(char ***) $13 = 0x00007fff5fbff848(lldb) p i(int) $14 = 3(lldb) p array(char *) $15 = 0x00007fff5fbff88c "afsdfsdfdf"(lldb) p *array(char) $16 = 'a'(lldb) p *(array + i)(char) $17 = 'd'(lldb) p (array + i)(char *) $18 = 0x00007fff5fbff88f "dfsdfdf"

Breakpoint 3:

(lldb) p **pa(char) $19 = 'd'(lldb) p *pa(char *) $20 = 0x00007fff5fbff88f "dfsdfdf"(lldb) p pa(char **) $21 = 0x00007fff5fbff880(lldb) p &pa(char ***) $22 = 0x00007fff5fbff848

Breakpoint 4:

(lldb) p *p(char) $23 = 'd'(lldb) p p(char *) $24 = 0x00007fff5fbff88f "dfsdfdf"(lldb) p &p(char **) $25 = 0x00007fff5fbff880

Analysis by memory distribution chartAs follows:

The whole process is actually to pass the address & P: 0x00007fff5fbff880 into the find1 function, by changing the value stored in this address & P: 0x00007fff5fbff880 (p) (another address ), the number of targets (* P) to be modified.

When passed in, the value of & P: 0x00007fff5fbff880 is 0x0000000000000000, and the number of objects stored in 0x0000000000000000 is '\ 0 ',

Run the * pA = array + I; command to change the value 0x0000000000000000 in & P: 0x00007fff5fbff880 to 0x00007fff5fbff88f.

In this process, the value stored in & P: 0x00007fff5fbff880 in the main () function is 0x00007fff5fbff88f, and the target number (* P) of 0x00007fff5fbff88f is 'D '.

This achieves the goal of modifying the number of targets.