C程序习题-取出某几位数[12.1]

时间：2010-09-25 来源：chengxiaopeng

编写一个函数getbits,从一个16位的单元中取出某几位（即该几位保留原值，其余位为0）。函数的调用形式为 getbits(value,n1,n2);value为该16位（2个字节）中的数据值，n1为欲取出的起始位，n2为欲取出的结束位，例如getbits(0101675,5,8)表示对八进制101675这个数，取出它的从左面起第5位到第8位。代码如下：

#include <stdio.h>

unsigned short int getbits(unsigned short value,int n1,int n2);
int main(int argc,char *argv[])
{
    unsigned short int a;
    int n1,n2;
    printf("input an octal number:");
    scanf("%o",&a);
    printf("input n1,n2:");
    scanf("%d,%d",&n1,&n2);
    printf("result:%o\n",getbits(a,n1,n2));
    system("pause");
    return 0;
}
unsigned short int getbits(unsigned short value,int n1,int n2)
{
         unsigned short int z;
         z = ~0;
         z = (z >> n1) & (z << (16-n2));
         z = value & z;
         z = z >> (16 - n2);
         return z;
}