ç位域的内存使用情况 [英] C bitfields memory usage

问题描述

我需要在下面的表格来处理一些数据：

I need to deal with some data in the following form:

typedef struct{
    unsigned n1 : 12;
    unsigned n2 : 12;
    unsigned n3 : 12;
    unsigned n4 :  1;
    unsigned n5 : 35;
} data;

我确信，在他们总共数到9个字节。结果
但他们不..写9个字节，该结构的一个文件并读不会恢复所有的数据和的sizeof（数据）返回1​​6. < BR>
有什么问题吗？

I made sure that in total they count up to 9 bytes.
But they don't.. Writing 9 bytes of that struct to a file and reading it back doesn't restore all the data, and sizeof(data) returns 16.
What's the problem here ?

推荐答案

问题是一些填充正由编译器效率的原因说。

The problem is some padding is being added by the compiler for efficiency reasons.

此行​​为可以被覆盖。

This behavior can be overridden.

有关如何做到这一点用gcc看到迫使GCC对齐

For how to do this with gcc see forcing alignment in GCC

有关如何做到这一点在Visual C ++，请参阅：迫使排列在Visual C ++

For how to do this with visual c++ see: forcing alignment in Visual C++

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