Simulating the implementation of commonly used string functions

1. Find the implementation char *  my_strstr of substring function strstr (const char * dest, const char  * SRC)//const protection string is not changed {assert (dest); assert (SRC);      //assert char *  ptr1 = null;char * ptr2 = src;while  (*dest) {ptr1 = dest;// The same pointer while  (*DEST == *SRC) {dest++; src++;if) of the string is retained after the match succeeds after the position pointer src = ptr2;//retention match fails.   (*src ==  ') return ptr1;//match successfully, return to the first address}dest++;} return null;//matching Failure} Advantages: The program is simple and easy to understand disadvantages: the search efficiency is lower than 2, the simulation string copy function strcpy implementation char * my_strcpy (char *  DEST, CONST CHAR * SRC) {assert (dest); assert (SRC);//Assert const char *ret =  dest;//keep the target string's head pointer while  (*SRC) {*dest++ = *src++;//copy}*dest =  '} One by one;//Will ' \ 0 ' Copy return  ret;//returns the first address of the target string} disadvantage: the copy encountered ' \ ' at the end, and cannot copy some of the string containing '. For example: char arr[10] = {0,0,0,0,0};3, string length calculation function Strlen 3 implementations of function 1) Use counter Int my_strlen_count (const  CHAR * STR)//counter implements the string length calculation function {assert (str);//Assert int count = 0;while  (*STR) {count++; str++;} return count;//return length}2) use pointer subtraction int my_strlen_ptr (CONST CHAR * STR)//Use pointer subtraction to achieve string length calculation { ASSERT (str);//Assert const char * ret = str;while  (*str++) {;} return  (str - ret - 1);//return length}3) use function recursion to extract INT MY_STRLEN_RECU (const char  * STR)//Use recursion to calculate string length {assert (str);//Assert if  (*str !=  ') {return  (MY_STRLEN_RECU (str  + 1)  + 1);} elsereturn 0;} 4, the string connection function Strcat implementation Char * my_strcat (CHAR * DEST, CONST CHAR * SRC)// String Join function {assert (dest); assert (SRC);//Assert char *ret = dest;//retain the target string's head pointer while  (*dest) {dest++;} Find ';while  ' (*dest++ = *src++)//connect src to dest{;} return ret;//returns the first address of the target string}5, the implementation of the string comparison function strcmp int my_strcmp (const char *str1, const  CHAR *STR2)//string comparison function {assert (sTR1); assert (str2);//Assert while  (*STR1 == *STR2) {str1++;str2++;if  ('  == *str1 ') { return 0;//equal}}return *str1 - *str2;//, returns the difference of ASCII codes of unequal characters}

Simulating the implementation of commonly used string functions