Simulating the implementation of partial library functions (Strcpy,strcmp,strcat,strstr,memcpy,memmove,memset)

1.strcpy (copy) char* my_strcpy (CHAR*DST,&NBSP;CONST&NBSP;CHAR*SRC) { assert (DST);  assert (SRC);  char* cp = dst; while  (*cp++ = *src++)  {  ; } &NBSP;RETURN&NBSP;DST;} 2.strcat (Connection) Char* my_strcat (CHAR*DST,&NBSP;CONST&NBSP;CHAR*SRC) { assert (DST);  assert (SRC);  char* cp = dst; while  (*cp !=  ')  {  cp++; }  while  (*cp++ = *src++)  {  ; } return dst;} 3.STRCMP (Compare) int my_strcmp (CONST&NBSP;CHAR*DST,&NBSP;CONST&NBSP;CHAR*SRC) { assert (DST);  assert (SRC); int ret = 0; while  (! ( ret=* (unsigned char*) dst - * (unsigned char*) src)  && *dst)  {   dst++;  src++; } if  (ret > 0)  {  ret = 1;  } else if  (ret < 0)  { &nbsP;ret = -1; } return ret;} 4.strstr  (looking for substrings) Char* my_strstr (CONST&NBSP;CHAR*DST,&NBSP;CONST&NBSP;CHAR*SRC) {&NBSP;CHAR*&NBSP;CP  =  (char*) src; char*s1; char*s2; if  (!*DST)  {  return  ((Char *) src); } while  (*CP)  {  s1 = cp;  s2 =  (char*) DST ;  while  (! ( *S1-*S2) &&*s1&&s2)   {   s1++;   s2++;  }   if  (!*S2)   {   return  (CP);  }  cp++;  } return  (NULL);} 5.memcpy (memory copy, non-overlapping) void* my_memcpy (Void *dst, const void*src, size_t count) {  assert (DST);  assert (SRC); char*ret =  (char*) dst; while  (count--)  {   * (char*) dst = * (char*) src;  dst =  (char*) dst + 1;   src =  (char*)Src + 1; } return ret;} 6.memmove (memory move for overlapping copies)//memory movement There are two cases: if there is a string: abcdefgh  If dst<src, that is, DST is in front of SRC, there is no overlap. If DST&GT;SRC, that is, DST is behind SRC, at this point if srt+count<dst, there is no overlap. If DST&GT;SRC, that is, DST after SRC, at this time if SRT+COUNT&GT;DST, then there is overlap, at this time from the back forward, from Src+count to start copying to Dst+count. Void *my_memmove (Void*dst, const void*src, size_t count) { assert (DST);  ASSERT (SRC); void *ret = dst; if  ((DST&NBSP;&LT;&NBSP;SRC)  | |   ((char*) src + count)  <  (char*) DST)      //memory does not overlap and is copied sequentially  {  while  (count--)   {   * (char*) dst = * (char*) src;    dst =  (char*) dst + 1;   src =  (char*) src +  1;  } } else                                                    //overlap, copy  {  dst =  reverse (char*) dst + count -  1;  src =  (char*) src + count - 1;  while  (count-- )   {   * (char*) dst = * (char*) src;   dst =  (char*) dst - 1;   src =  (char*) Src - 1;  } } return  ret;} 7.memset (Memory setting) Void* my_memset (void*dst, int val, size_t count) { void*start  = dst; while  (count--)  {  * (char*) dst =  (char) val;   dst =  (char*) Dst + 1; } return start;}

This article is from the "printf Return Values" blog, so be sure to keep this source http://10741125.blog.51cto.com/10731125/1782572

Simulating the implementation of partial library functions (Strcpy,strcmp,strcat,strstr,memcpy,memmove,memset)