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[h2]1¡¢void *mymemcpy(void *dest, const void* src, size_t n)£»[/h2]
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1. void* memcpy(void* dest,void* src,size_t n){
2.     assert(dest != NULL && src != NULL);
4.     if(src < dest && (char*)src + n > dest){
5.         char* pdst = (char*)dest+n-1;
6.         char* psrc = (char*)src+n-1;
7.         while(n--){
8.             *pdst-- = *psrc--;
9.         }
10.     }else{
11.         char* pdest = (char*)dest;
12.         char* psrc = (char*)src;
13.         while(n--){
14.             *pdest++ = *psrc++;
15.         }
16.     }
17.     return dest;
18. }

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[h2][/h2][h2]2¡¢void *memset(void *s, int c, size_t n);[/h2]

1. void* memset(void* src,int c,size_t n){
2.     assert(src != NULL);
3.     char* psrc = (char*)src;
4.     while(n--){
5.         *psrc++ = (char)c;
6.     }
7.     return src;
8. }

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[h2][/h2][h2]3¡¢char* strcpy(char* dest,const char* src);[/h2]

1. char* strcpy(char* dest,const char* src){
2.     assert(dest != NULL && src != NULL);
4.     size_t n = strlen(src);
5.     if(src < dest && src + n > dest){
6.         char* pdst = dest + n;
7.         *pdst-- = '\0';
8.         src = src + n - 1;
9.         while(n--){
10.             *pdst-- = *src--;
11.         }
12.     }else{
13.         char* pdst = dest;
14.         while((*pdst++ = *src++) != 0);
15.     }
16.     return dest;
17. }

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4¡¢char* mystrncpy(char* dest,char* src,size_t n);

1. char* strncpy(char* dest,const char* src,size_t n){
2.     assert(dest != NULL && src != NULL);
4.     if(src < dest && src + n > dest){
5.         int m = strlen(src) < n ? strlen(src):n;
6.         char* pdst = dest+m;
7.         *pdst-- = '\0';
8.         src = src + m-1;
9.         while(m--){
10.             *pdst-- = *src--;
11.         }
12.     }else{
13.         char* pdst = dest;
14.         size_t i = 0;
15.         while(i++ < n && (*pdst++ = *src++) != '\0');
16.         if(*(pdst-1) != '\0') *pdst = '\0';
17.     }
18.     return dest;
19. }

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[h2][/h2][h2]5¡¢char* strcat(char* dest,const char* src)[/h2]

1. char* strcat(char* dest,const char* src){
2.     assert(dest != NULL && src != NULL);
3.     char* pdst = dest;
4.     while(*pdst != '\0'){
5.         pdst++;
6.     }
7.     while((*pdst++ = *src++) != '\0');
8.     return dest;
9. }

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[h2][/h2][h2]6¡¢int strcmp(const char* s1,const char* s2)[/h2]

1. int strcmp(const char* s1,const char* s2){
2.     assert(s1 != NULL && s2 != NULL);
3.     while(s1 && s2 && *s1 == *s2){
4.         s1++;
5.         s2++;
6.     }
7.     return *s1 - *s2;
8. }

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[h2][/h2][h2]7¡¢size_t strlen(const char* s)[/h2]

1. size_t strlen(const char* src){
2.     assert(src != NULL);
3.     size_t ret = 0;
4.     while(*src++ != '\0'){
5.         ret++;
6.     }
7.     return ret;
8. }

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