模拟实现strcmp、strstr、memcpy、memmove

本文主要是介绍模拟实现strcmp、strstr、memcpy、memmove，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

#define _CRT_SECURE_NO_WARNINGS 1#include <stdio.h>
#include <assert.h>
#include <windows.h>  
#include <stdlib.h>#模拟实现memmove函数
void *my_memmove(void *dest,const void *src,size_t count)  
{  void *ret = dest;  assert(dest);  assert(src);  if((src<dest)&&((char*)dest<(char*)src+count))  {  while(count--)  {  *((char*)dest+count)=*((char*)src+count);  }  }  else  {  while(count--)  {  *(char*)dest=*(char*)src;  dest=(char*)dest+1;  src=(char*)src+1;  }  }  return ret;  
}  
int main()  
{  int i=0;  int arr[]={1,2,3,4,5,6,7,8,9,0};  int sz=sizeof(arr)/sizeof(arr[0]);  my_memmove(arr+3,arr,4*sizeof(int));  for(i=0;i<sz;i++)  {  printf("%d ",arr[i]);  }    return 0;  
}  #模拟实现memcpy函数
void* my_memcpy(void* dest, const void* src,size_t count)  
{  void *ret = dest;  assert(dest);  assert(src);  while(count)  {  *(char *)dest = *(char *)src;  dest = (char *)dest+1;  src = (char *)src+1;  count--;  }  return ret;  
}  
int main()  
{  char arr[] = {"hello"};  char str[] = {"bit"};  int sz = sizeof(arr)/sizeof(arr[0]);  int i=0;  char *ret=my_memcpy(arr,str,7);  printf("%s\n",ret);  return 0;  
} #模拟实现strstr函数 
char *my_strstr(const char *str, char *string)
{int i=0;assert(str&&string);   while('\0'!=str)       { while(1){if(string[i]!=str[i])   break;if(string[i]=='\0')      return str;i++;}string++;}return NULL;
}int main()
{char string[] = "bcde";char str[] = "abcdef"; char *p=my_strstr(str,string);int result=p-str+1;    if(p!=NULL)  printf("%s found at position %d\n\n", string,result);elseprintf( "%s not found\n", string);return 0;
}#模拟实现strcmp函数int my_strcmp(const char *str1, const char *str2)  
{  assert(str1);  assert(str2);  while (*(str1) == *(str2))  {  if (*str1 == '\0')  return 0; str1++;  str2++;  } return *str1 - *str2;}  
int main()  
{  char *p1 = "ab";  char *p2 = "abcd";       printf("%d\n", my_strcmp(p1, p2));                return 0;  
}