1.模擬實現strncpy

//1.模擬實現strncpy(拷貝前n個字元)
#include<stdio.h>
#include<assert.h>
char * my_strncpy(char *dest,const char *src,size_t num)
{
 	char *p = dest;
 	int i = 0;
 	assert(dest != NULL);
 	assert(src != NULL);
 	while(num--)
 	{
  		*(dest + i) = *(src + i);
  		i++;
 	}
 	return p;
}
int
 
 main()
{
	 char a1[1024] = {0};
	 char a2[1024] = "asdfgh";
	 my_strncpy(a1,a2,3);
	 puts(a1);
	 return 0;
}

2.模擬實現strncat

//2.模擬實現strncat(拼接前n個字元)
#include<stdio.h>
#include<assert.h>
char * my_strncat(char *dest,const char *src,size_t num)
{
	 char *ret = dest;
	 int i = 0;
	 assert(dest != NULL
 
);
	 assert(src != NULL);
	 while(*dest != '\0')
	 {
	        dest++;
	 }
	 while(num--)
	 {		
		*(dest + i) = *(src + i);
		i++;
	 }
	 return ret;
}
int main()
{
	 char a1[1024] = "today is";
	 char a2[1024] = " a good day or not";
	 my_strncat(a1,a2,11);
	 puts(a1);
	 return 0;
}

3.模擬實現strncmp

//3.模擬實現strncmp(前n個字元比較)
 

#include<stdio.h>
#include<assert.h>
int my_strncmp(const char *dest,const char *src,size_t num)
{
	 int i = 0;
	 assert(dest != NULL);
	 assert(src != NULL);
	 while(num--)   //a1>a2返回1，a1<a2返回-1，等於返回0
	 {
		  if(*(dest + i) == *(src + i))
		  {
		   	i++;
		  }
		  else if(*(dest + i) > *(src + i))
		  {
		   	return 1;
		  }
		  else
		  {
		   	return -1;
	 	  }
 	}
 	return 0;
}
int main()
{
	 char a1[1024] = "zabcd";
	 char a2[1024] = "fabc";
	 printf("%d\n",my_strncmp(a1,a2,2));//根據字典序，此處應輸出數字1
	 return 0;
}