（26）4.7 字符函数和字符串函数

#include<stdio.h>
#include<string.h>
#include<assert.h>
//int my_strcmp(const char* str1, const char* str2)
//{
//   assert(str1 && str2);//指针有效性，不能为空指针
//   while (*str1 == *str2)
//   {
//       if (*str1 == '\0')
//           return 0;//相等的情况
//       str1++;
//       str2++;
//   }
//   if (*str1 > *str2)
//       return 1;
//   else (*str1 < *str2)
//       return -1;
//}
//简化
int my_strcmp(const char* str1, const char* str2)
{
   assert(str1 && str2);//指针有效性，不能为空指针
   while (*str1 == *str2)
   {
       if (*str1 == '\0')
           return 0;//相等的情况
       str1++;
       str2++;
   }
   return(*str1 - *str2);
}
int main()
{
   char arr1[] = "abcde";
   char arr2[] = "abcf";
   int ret = my_strcmp(arr1, arr2);
   if (ret < 0)
       printf("<");
   if (ret == 0)
       printf("==");
   if (ret> 0)
       printf(">");

   return 0;
}
效率比较低
char* my_strstr(const char* str1, const char* str2)
{
   assert(str1 && str2);
   const char* s1 = str1;
   const char* s2 = str2;
   const char* p = str1;

   while (*p)
   {
       s1 = p;
       s2 = str2;
       while (*s1 != '\0' && *s2 != '\0' && *s1 == *s2)
       {
           s1++;
           s2++;
       }
       if (*s2 == '\0')
       {
           return(char*)p;
       }
       p++;
       return NULL;
   }

}
int main()
{
   char email[] = "zpw@bitejiuyeke.com";
   char substr[] = "bitejiuyeke";
   char* ret = my_strstr(email, substr);
   if (ret == NULL)
   {
       printf("子串不存在\n");
   }
   else
   {
       printf("%s\n", ret);
   }
   return 0;
}
KMP算法
这个算法也是用来实现一个字符串中查找字符串的
效率高，但实现难度大
B站搜索：比特大博哥，可以找到KMP算法实现
strtok 切
int main()
{
   const char* sep = "@.";
   char email[] = "zhangpengwei@bitjiuyeke.com";
   char cp[30] = { 0 };
   //strcpy(cp, email);
   //char* ret = strtok(cp, sep);
   //printf("%s\n", ret);

//char* ret = strtok(NULL, sep);
//printf("%s\n", ret);

   //char* ret = strtok(NULL, sep);
   //printf("%s\n", ret);
   //简化
   char* ret = NULL;
   for (ret = strtok(cp, sep); ret != NULL; ret = strtok(NULL, sep))
   {
       printf("%s\n", ret);
   }
   return 0;
}
///memcpy两块独立数据之间的拷贝函数，不能对同一块空间重叠拷贝与之对应的memmove
void* my_memcpy(void* dest, const void* src, size_t num)
{
   assert(dest && src);
   void* ret = dest;
   while (num--)
   {
       *(char*)dest = *(char*)src;
       dest = (char*)dest + 1;
       src = (char*)dest + 1;