在结构安排领域哪种方式更好？ [英] Which way of arranging fields in structure is better?

问题描述

我有两种方法来安排结构中的字段

I have two ways to arrange the fields in a structure

  struct foo {  
    float   a;
    double  b;
    float   c;
    double  d;
    short   e;
    long    f;
    short   g;
    long    h;
    char    i;
    int     j;
    char    k;
    int     l;
  };




  struct foo {  
    double  b;
    double  d;
    long    f;
    long    h;
    float   a;
    float   c;
    int     j;
    int     l;
    short   e;
    short   g;
    char    i;
    char    k;
  };

哪一个应实行为什么？

Which one should be practiced and why?

推荐答案

来安排结构成员的最好办法是把他们在递增顺序，通过它们的大小。 这样做，可以减少填充 ，需要数据对齐。

The best way to arrange members of a structure is to put them in increasing order, by their size. Doing this, you reduce the padding, required for data alignment.

此外，使用一些 preprocessor指令你修改对齐，例如：

Also, using some preprocessor directives you modify the alignment, for example:

#define packed_data __attribute__((__packed__))

将其关闭。用这种方法，成员为了此事doesen't了，但我坚决取缔这种做法，因为内存alingnment的性能得到优化。

turns it off. Using this, the member order doesen't matter anymore, but I strongly discourage this, as the memory alingnment is optimised for performance.

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