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1、void *mymemcpy(void *dest, const void* src, size_t n)； 内存拷贝函数，memcpy函数的功能是从源src所指的内存地址的起始位置开始拷贝n个字节到目标dest所指的内存地址的起始位置中 " D1 R1 _! B) U* a- q- D, R void* memcpy(void* dest,void* src,size_t n){assert(dest != NULL && src != NULL); if(src < dest && (char*)src + n > dest){$ W. u3 z4 _- O char* pdst = (char*)dest+n-1;) o7 ^" o& B9 x, v. @1 z( c char* psrc = (char*)src+n-1;: J0 I m1 ?; y* s) d7 h0 G while(n--){7 f6 P1 Q& i) k *pdst-- = *psrc--; } }else{ char* pdest = (char*)dest;$ a" V% Y1 G# J& v char* psrc = (char*)src; while(n--){) V- b) v+ D. F; }* S0 M *pdest++ = *psrc++; }- q k1 U* S3 B1 e4 W }1 D$ Q( L) e3 b- v- u& ~ return dest; } 2、void *memset(void *s, int c, size_t n); % T# a/ m! Z2 w3 k5 g( M, {8 L void* memset(void* src,int c,size_t n){3 c$ q* F4 d0 k6 K/ Dassert(src != NULL); char* psrc = (char*)src;5 V; J( l# [; h- f. n while(n--){ *psrc++ = (char)c; }- f$ x. j# ?2 |5 u) L return src; } 3、char* strcpy(char* dest,const char* src); assert(dest != NULL && src != NULL); size_t n = strlen(src); if(src < dest && src + n > dest){! F) H/ Z1 }& F: k8 k4 W3 o char* pdst = dest + n; *pdst-- = '\0';6 D$ q& P* I$ N src = src + n - 1; while(n--){ *pdst-- = *src--;8 _$ J- z k& O' F( R } }else{ char* pdst = dest; while((*pdst++ = *src++) != 0); }8 A+ \* u6 B/ @) H) _5 d& ]9 [7 K return dest; } `7 l: e6 T' \, a- u* P4 ^% t 4、char* mystrncpy(char* dest,char* src,size_t n); assert(dest != NULL && src != NULL);5 l) e1 C4 I- c- i4 d. {$ ` if(src < dest && src + n > dest){ int m = strlen(src) < n ? strlen(src):n;/ e5 X- G9 b8 D0 [' Y1 ` char* pdst = dest+m; *pdst-- = '\0'; src = src + m-1; while(m--){ *pdst-- = *src--;3 S$ f- ]# F. o( s, d0 ~- P7 Q8 [0 ]2 p }, a0 r/ y0 W$ W8 [; L6 u }else{8 m: Y# l$ S& f% F- N- n char* pdst = dest; size_t i = 0; while(i++ < n && (*pdst++ = *src++) != '\0'); if(*(pdst-1) != '\0') *pdst = '\0'; }- i' J) L. m7 b6 L% K0 B return dest;9 |% U5 t5 ~9 s } 5、char* strcat(char* dest,const char* src) 9 x: {! t) Z% V5 i6 O- I% H6 U) A/ H char* strcat(char* dest,const char* src){9 x* i. x5 w/ q% i% ]assert(dest != NULL && src != NULL);5 v# G1 _$ u+ n- k char* pdst = dest;$ e: x% j) F1 L( v while(*pdst != '\0'){ pdst++;9 T t0 I, G9 p2 G }& x/ m6 Y4 @7 r3 c+ e4 e7 F while((*pdst++ = *src++) != '\0');) y' b; |' c; N5 P4 o return dest; }3 K& b+ B+ i7 k; P c0 p1 \ 6、int strcmp(const char* s1,const char* s2) assert(s1 != NULL && s2 != NULL); while(s1 && s2 && *s1 == *s2){4 l% h: I E, u9 g3 r6 @, I5 w s1++; s2++; }+ J+ r, Y2 K5 m& t return *s1 - *s2; } 7、size_t strlen(const char* s) assert(src != NULL);. v& T- v, r: g6 a$ y4 ]1 M! V size_t ret = 0; while(*src++ != '\0'){( p' o0 N& t8 P4 h ret++;& t' v& g5 S. f- c4 f }# d8 @) N* b; @# Q$ g, Y* Y return ret; } |
| 用库省心一些 |
