模拟实现memcpy/memmove/memset

小咪咪 2022-09-21 11:43 204阅读 0赞

1.模拟实现memcpy

//memcmp
    #include<stdio.h>
    #include<stdlib.h>
    #include<assert.h>
    int my_memcmp(const char* str1, const char* str2, int num)
    {
    	assert(str1 != NULL &&str2 != NULL);
    	while (num--&&*str1==*str2)
    	{
    		str1++;
    		str2++;
    	}
    	if (num == 0)
    		return 0;
    	else
    		return *str1 - *str2;
    
    }
    int main()
    {
    	char str1[] = "aabbccdd";
    	char str2[] = "aabbccdf";
    	int ret=my_memcmp(str1, str2, sizeof(str1));
    	printf("%d\n", ret);
    	system("pause");
    	return 0;
    }

2.模拟实现memmove

memmove 
    //从源目标字符串中，拷贝count个字符，如果出现内存重叠问题，就会从后向前进行拷贝
    //如果没有，就会想memcopy一样进行拷贝
    
    #include<stdio.h>  
    #include<assert.h>  
    
    void *my_memmove(void *dest, void *str, size_t len)
    {
    	assert(dest);
    	assert(str);
    	char *pdest = (char *)dest;
    	char *pstr = (char*)str;
    	if ((pstr < pdest) && (pdest < pstr + len))  //源和目标有重叠的情况，从后往前拷贝  
    	{
    		while (len--)
    		{
    			*(pdest + len) = *(pstr + len);
    		}
    	}
    	else            //没有重叠，从前往后拷贝  
    	{
    		while (len--)
    		{
    			*pdest = *pstr;
    			pdest++;
    			pstr++;
    		}
    	}
    	return dest;
    }
    
    int main()
    {
    	int i = 0;
    	int arr[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 };
    	int size = sizeof(arr) / sizeof(arr[0]);
    	my_memmove(arr, arr + 3, 8);  //注意这里的长度是以一字节为单位的  
    	for (i = 0; i <size; i++)
    	{
    		printf("%d ", arr[i]);
    	}
    
    	system("pause");
    	return 0;
    }

3.模拟实现memset

//memset
    #include<stdio.h>
    #include<assert.h>
    void* my_memset(char * ptr, int value, size_t num)
    {
    	assert(ptr);
    	for (int i = 0; i < num; i++)
    	{
    		ptr[i] = value;
    	}
    }
    int main()
    {
    	char str[] = "almost every programmer should know memset!";
    	my_memset(str, '-', 6);
    	printf("%s\n", str);
    	system("pause");
    	return 0;
    }