C语言常用库函数的使用及模拟实现详解例举

int my_strlen(dest)
{
int count=0;
    while(dest)//当dest等于'\0'时停止循环
{
    count++;
    dest++;
}
return count;
}

int my_strlen(char* dest)
{
    int count=0;
    if(*dest!='0')
    {
        dest++;
        count++;
        return my_strlen(dest,count)
    }
    else
    return count;
}

int my_strlen(char* dest)
{
    char* arr=dest;//定义一个新指针指向dest
    while(*arr)//直到arr指向'\0'
    {
    arr++;
    }
    return (arr)-(dest);//指针相减代表两个指针之间的元素个数
}

char* my_strcpy(char* dest, const char* str)
{
	char* arr1 = dest;
	while ((*dest++ = *str++)!='\0')
	{
		;
	}
	return arr1;
}
int main()
{
	char arr1[] = "***************";
	char arr2[] = "hello word";
	my_strcpy(arr1, arr2);
	printf("%s", arr1);
	return 0;
}

int my_strcmp(char* arr1,char* arr2)
{
	while(*arr1 == *arr2)
	{
		if (*arr1 == '\0' && *arr2 == '\0')
		{
			return 0;
		}
		else
		{
			arr1++; arr2++;
 
		}
	}if (*arr1 > *arr2)
	{
		return 1;
	}
	else if (*arr1 < *arr2)
	{
 
		return -1;
	}
}

char* my_strcat(char* dest, char* str)
{
	char* ret = dest;
	while (*dest)
	{
		dest++;
	}
	while (*dest++=*str++)
	{
		;
	}
	return ret;
}
int main()
{
	char arr1[50] = "hello";
	char arr2[] = "word";
	char* count=my_strcat(arr1, arr2);
	printf("%s", count);
	return 0;
}

char* my_strstr(char* dest, char* str)
{
	char* arr1 = str;
	char* cur = dest;
	while (*cur)
	{
		str = arr1;
		dest = cur;
		if (*dest != *str)
		{
			dest++;
			str++;
		}
		else if (*dest == *str)
		{
			while (*dest == *str)
			{
				dest++; str++;
 
			}if (*str == '\0')
			{
				return cur;
			}
		}
		cur++;
	}return NULL;
}
int main()
{
	char arr1[] = "abbbcdef";
	char arr2[] = "bbc";
	char* ret=my_strstr(arr1, arr2);
	if (NULL == ret)
	{
		printf("找不到子串\n");
	}
	else
	{
		printf("%s\n", ret);
	}
	return 0;
}

int main()
{
	char buff[] = "www.aaabbbccc@qq.com";
	char buf[20] = { 0 };
	strcpy(buf, buff);
	char* sep=".@";
	char* str = NULL;
	for (str = strtok(buf, sep); str != NULL; str = strtok(NULL, sep))
			{//NULL是从保存好的位置开始往后找
				printf("%s\n", str);
			}
	return 0;
}

void* my_memmove(void* dest,void* str , size_t count)
{
	void* ch = dest;
	if (dest > str)
	{
		while (count--)
		{
			*((char*)dest + count) = *((char*)str + count);
		}
	}
	else
	{
		while (count--)
		{
			*(char*)dest = *(char*)str;
			dest=(char*)dest+1;
			str=(char*)str+1;
		}
	}
}
int main()
{
	int arr1[10] = {1,2,3,4,5,6,7,8,9,10};
	my_memmove(arr1+2, arr1 , 20);
	int sz = sizeof(arr1) / sizeof(arr1[0]);
	for (int i = 0; i < sz; i++)
	{
		printf("%d", arr1[i]);
	}
	return 0;
}

void* my_memcmp(char* arr, char* arr1, int count)
{
	while (count--)
	{
		if (*(char*)arr > *(char*)arr1)
		{
			return 1;
		}
		else if ((*(char*)arr < *(char*)arr1))
		{
			return -1;
		}
		arr++; arr1++;
	}	return 0;
}
int main()
{
	int arr[] = { 1,2,3,4,5 };
	int arr1[] = { 1,2,3,4,4 };
	int ret=my_memcmp(arr, arr1, 20);
	printf("%d", ret);
	return 0;
}