字符串内置函数的实现

Posted 2021-01-22 susidian

 1 char *MyStrcpy(char *des,const char *src)
 2 {
 3 assert(des != NULL && src != NULL);
 4 char *pstr = des;
 5 while((*pstr++ = *src++)!= ‘‘);
 6 return des;
 7 }
 8 
 9 char *MyStrcat(char *des,const char *src)
10 {
11 assert(des != NULL && src!= NULL);
12 char *pdes = des;
13 while(*pdes != ‘‘) ++pdes;
14 while((*pdes++ = *src++) != ‘‘);
15 return des;
16 }
17 
18 void *MyMemcpy(void *des,const void *src,unsigned int count)
19 {
20 assert(des !=NULL && src != NULL && count>0);
21 char *pdes = (char *)des;
22 int i=0;
23 while(i<count && *(char *)src != ‘‘)
24 {
25 *pdes++=*(char *)src;
26 src=(char *)src+1;
27 ++i;
28 }
29 *pdes = *(char*)src;
30 return des;
31 }
32 
33 void* MyMemmove(void *des,const void *src,unsigned int count)
34 {
35 assert(des != NULL && src != NULL && count >0);
36 char *pdes = (char *)des;
37 if(des < src || (char *)des >(char *)src + count)
38 {
39 int i = 0;
40 while(i<count && *(char *)src != ‘‘)
41 {
42 *pdes++ = *(char *)src;
43 src = (char *)src+1;
44 ++i;
45 }
46 }
47 else
48 {
49 pdes = pdes + count;
50 src = (char *)src + count -1;
51 *pdes-- = ‘‘;
52 int i= count -1;
53 while(i>=0)
54 {
55 *pdes--=*(char *)src;
56 i--;
57 src = (char *)src -1 ;
58 }
59 }
60 return des;
61 }