编程题四

1、编写内存拷贝函数，不用库函数

函数原型：void* memcpy(void *pvTo, const void *pvFrom, size_t size)

答：

void my_memcpy(void *dest, const void *src, size_t size)

{

assert( dest !=NULL);//判断传入的是否为空

assert(src !=NULL);

unsigned char* pdest = (unsigned char*)dest; //将void* 转换为 char*

const unsigned char *psrc = (unsigned char*)src;

assert(!(psrc<=pdest&&pdest<psrc+size));

assert(!(pdest<=psrc&&psrc<pdest+size));

while(size--)

{

*pdest = *psrc;

pdest++;

psrc++;

}

return dest;

}

2、用C写一个输入的整数，倒着输出整数的函数，要求用递归方法。

答：

void func(int n)

{

printf("%d",n%10);

n/=10;

if(n<0)

{return;}

func(n);

}

3、编写一个函数，作用是把一个char组成的字符串循环右移n个。比如原来是“abcdefghi”，如果n= 2, 移位后应该是“hiabcdefg”。

答：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <iostream>
using namespace std;


char* func(char *des, char *src, int n)
{
char* dest = des;
int num = strlen(src);
int i = 0;
char temp[10] = { 0 };
while (*(src + n) != '\0')
{
temp[i] = *src;
i++;
*(src++);
}
while (*src != '\0')
{
*dest = *src;
*src++;
*dest++;
}
for (i = 0; i < num - n; i++)
{
*dest = temp[i];
*dest++;
}
*dest = '\0';


return des;
}


int main()
{
char *src = "abcdefghi";
char dest[10] = { 0 };
// func(dest,src,2);
//cout << dest << endl;


//cout << func(dest,src,2) << endl;
printf("%s\n", func(dest,src,2));
system("pause");
return 0;
}