无法为浮点值保存到一个位域结构 [英] Unable to save a float value to a bitfield structure

问题描述

我有一个结构

struct {
   u32 var1 :7;
   u32 var2 :4;
   u32 var3 :4;
   u32 var4 :1;
   u32 var5 :4;
   u32 var6 :7;
   u32 var7 :4;
   u32 var8 :1;
        } my_struct;

my_struct struct1[10];

for(int i=0;i<10; i++)
  {
    // left some portion
    struct1[i].var5= x;// where x is a float value retrieved from a database with sqlapi++ asDouble()

    cout<<"Value of x from db is:\t"<<x;   // prints 0.1 if it is stored, prints 2.4 if 2.4 is fed

    cout<<"Value of x stored in struct1 is:\t"<<struct1[i].var5;   // prints 0 instead of 0.1, prints 2 instead of 2.4
  }

我要存储浮点值0.1一样，3.4，0.8 VAR5。但我不能这样做。有人可以帮我我怎么能解决这个问题？

I want to store floating point values like 0.1, 3.4, 0.8 in var5. But i am unable to do so. Can somebody help me how could i fix this problem?

推荐答案

VAR5 是可以保存值0..15一个4位无符号整数（上一个工作合理的假设，即 U32 是东西的代名词像 unsigned int类型）。

var5 is a 4-bit unsigned integer that can hold values 0..15 (working on a reasonable assumption that u32 is a synonym for something like unsigned int).

您不能分数值存储在里面。 0.1 和 0.8 将被存储为 0 ; 3.4 将被存储为 3 。

You can't store fractional values in it. 0.1 and 0.8 would be stored as 0; 3.4 would be stored as 3.

如果你真的想分数，你将不得不解决如何重新present他们（定点算术）。

If you really want fractions, you're going to have to work out how to represent them (fixed point arithmetic).

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