strlen,strcpy,strcat,strcmp,strstr,memcpy,的模拟实现方式

#include<stdio.h>#include<stdlib.h>#include<Windows.h>#include<string.h>#include<assert.h>//模拟实现strlen三种实现方式int my_strlen_1(const char* str){    //使用计数器实现    int count = 0;    assert(str);    while(*str)    {        count++;        str++;    }    return count;}//第二种递归实现int my_strlen_2(const char* str){    assert(str);    if(*str != '\0')        return 1+my_strlen_2(str+1);    else        return 0;}//指针减指针模拟实现int my_strlen_3(const char* str){    const char *p = str;      while(*p)      {          p++;      }      return p-str;}int main(){    int len1 = my_strlen_1("abcdef");    int len2 = my_strlen_2("abcdef");    int len3 = my_strlen_3("abcdef");    printf("len1 = %d\n",len1);    printf("len2 = %d\n",len2);    printf("len3 = %d\n",len3);    system("pause");    return 0;}//模拟实现strcpychar* my_strcpy(char* dest,const char* src){    char *ret = dest;    assert(src != NULL);    assert(dest != NULL);    while(*dest++ = *src++)    {        ;    }    return ret;}int main(){    char arr[80]={0};    printf("string=%s\n",my_strcpy(arr,"hello world"));    system("pause");    return 0;}//模拟实现strcatchar *my_strcat(char *dest,char *src){    char *ret = dest;    assert(dest);    assert(src);    while(*dest)    {        dest++;    }    while(*dest++ = *src++)    {        ;    }    return ret;}int main(){    char arr1[15]="abcd";    char *arr2="ef";    printf("%s\n",my_strcat(arr1,arr2));    system("pause");    return 0;}//模拟实现strcmpint my_strcmp(const char* arr1,const char* arr2){  assert(arr1);  assert(arr2);  while(*arr1 == *arr2)  {   if(*arr1 == '\0')     return 0;   arr1++;   arr2++;  } return *arr1 - *arr2;}int main(){ char *arr1="abcdef"; char *arr2="abcd"; int ret=my_strcmp(arr1,arr2); printf("%d\n",ret); system("pause"); return 0;}//模拟实现strstrchar* my_strstr(const char* str, const char* substr)  {      const char* s1 = str;     const char* s2 = substr;      const char* ret = str;//ret就是用来保存首地址的      assert(str);      assert(substr);    if(strlen(s1)<strlen(s2))        return NULL;    while (*ret)      {          s1 = ret;s2 = substr;          while (*s1 && *s2 && (*s1 == *s2))          {              s1++;              s2++;          }          if (*s1 == '\0')          {              return NULL;          }          if(*s2 == '\0')            return ret;         ret++;    }      return NULL;  }  int main()  {      char a[20] = "abbbcdef";      char b[10] = "bbcde";      printf("%s\n", my_strstr(a, b));      system("pause");      return 0;  }  //模拟实现memcpyvoid* my_memcpy(void* dest, void* src,size_t n)  {      void* ret = dest;      char* str1 = (char*)dest;      char* str2 = (char*)src;      assert(dest);      assert(src);      while (n--)      {          *str1++ = *str2++;      }      return ret;  }  void* my_memmove(void* dest, void* src, size_t n)  {      void* ret = dest;      char* str1 = (char*)dest;      char* str2 = (char*)src;      assert(dest);      assert(src);      if (str1 > str2)       {          while (n--)          {              *(str1 + n) = *(str2 + n);          }      }      else      {          while (n--)          {              *str1++ = *str2++;          }      }      return ret;  }  int main()  {      int i = 0;      int arr1[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };      int arr2[10] = { 0 };      int arr3[10] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };      my_memcpy(arr2, arr1, sizeof(arr1));      my_memmove(arr3 + 5, arr3 + 4, 3 * sizeof(int));      for (i = 0; i < 10; i++)      {          printf("%d ", arr2[i]);      }      printf("\n");      for (i = 0; i < 10; i++)      {          printf("%d ", arr3[i]);      }      system("pause");      return 0;  }