c语言重要的字符串与内存函数

size_t my_strlen(const char*str)
{ 
  size_t count=0;
  while(*str)
  {
   str++;
   count++;
  }

int my_strcmp(const char*str1,const char*str2)
{
   while (*str1 == *str2)
   {
    if (*str1 && *str2)//判断'\0'
     return *s2 - *s1;
    *str1++;
    *str2++;
   }//循环结束标志*str1！=*str2
   return *str2 - *str1;
}

char *my_strcpy(char *dest, const char*src)
{ 
 char *ret = dest;
 while((*dest++ = *src++))
 {
  ;
 }
 return ret;
}

char* my_strcat(const char* str1, const char* str2)
{
 
  while (*str1) str1++;
  while (*(char*)str1++ = *(char*)str2++) {
   ;
  }
}

char* my_strstr(const char* str1, const char* str2)
{
 if (!*str2)//判断字符串是否为空
  return (char*)str1;

  char* ret1= (char*)str1;//将str类型转换
  
  char *cp = ret1;
 while (*ret1)
 {
  cp = ret1;
  char* ret2 =(char*) str2;
  while (*cp== *str2) {//遍历字符串
           
     if (!*ret2)//判断str2是否到达‘0'的位置
      return cp;
     cp++, ret2++;
  }
  ret1++;//循环结束没有返回，从下一个字符开始查找
  if (!*ret1)
   return NULL;
 }
 return NULL;
}

void * my_memcpy ( void * dst, const void * src, size_t count)
{
  void * ret = dst;
  while (count--) {
    *(char *)dst = *(char *)src;
    dst = (char *)dst + 1;
    src = (char *)src + 1;
  }
 
  return(ret);
}

int main()
{
 int arr1[10] = { 1,2,3,4,5,6,7,8,9,0 };
 // 预期结果       1 2 1 2 3 4 7 8 9 0
 my_memcpy(arr1+2, arr1, 16);

  for (int i = 0; i < 10; i++)
  {
   printf("%d ", arr1[i]);
 }
}

int main()
{
   int arr1[10] = { 1,2,3,4,5,6,7,8,9,0 };
   my_memcpy(arr1, arr1+2, 16);

    for (int i = 0; i < 10; i++)
    {
     printf("%d ", arr1[i]);
   }
}

**void* my_memmove(void* dest, void* src, size_t num)
{
 char* ret = dest;
 //如果指向同一块空间 判断地址大小，避免数据在被复制前被改变
 if ( (char*)dest-(char*)src< 0){
  while (num)
  {

   *((char*)dest)++ = *((char*)src)++;
   num--;
  }
 }
 else {
  while(num--){
   *((char*)dest+num) = *((char*)src+num);
  }
 }
 return ret;
}