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初识字节对齐 (一)

2014-11-23 23:12:01 · 作者: · 浏览: 14

标签: 初识字节

今天写程序的时候遇到一个小难题，如何记录下64个设备的有无动作的表示，我想到了节省资源的位域，写下如下的程序(32位PC下)

[cpp]

typedef struct

{

unsigned f1 : 1;

}new_log_t;

typedef struct

{

unsigned f1 : 1;

}new_log_t;sizeof(new_log_t) = 4，似乎没有节省资源吗，再试

[cpp]

typedef struct

{

unsigned f1 : 1;

unsigned f2 : 1;

unsigned f3 : 1;

unsigned f4 : 1;

unsigned f5 : 1;

unsigned f6 : 1;

unsigned f7 : 1;

unsigned f8 : 1;

}new_log_t;

typedef struct

{

unsigned f1 : 1;

unsigned f2 : 1;

unsigned f3 : 1;

unsigned f4 : 1;

unsigned f5 : 1;

unsigned f6 : 1;

unsigned f7 : 1;

unsigned f8 : 1;

}new_log_t;sizeof(new_log_t) = 4，似乎了解什么了，再试

[cpp]

typedef struct

{

unsigned f1 : 1;

unsigned f2 : 1;

unsigned f3 : 1;

unsigned f4 : 1;

unsigned f5 : 1;

unsigned f6 : 1;

unsigned f7 : 1;

unsigned f8 : 1;

unsigned f9 : 1;

unsigned f10 : 1;

unsigned f11 : 1;

unsigned f12 : 1;

unsigned f13 : 1;

unsigned f14 : 1;

unsigned f15 : 1;

unsigned f16 : 1;

unsigned f17 : 1;

unsigned f18: 1;

unsigned f19 : 1;

unsigned f20 : 1;

unsigned f21 : 1;

unsigned f22 : 1;

unsigned f23 : 1;

unsigned f24 : 1;

unsigned f25 : 1;

unsigned f26 : 1;

unsigned f27 : 1;

unsigned f28 : 1;

unsigned f29 : 1;

unsigned f30 : 1;

unsigned f31 : 1;

unsigned f32 : 1;

unsigned f33 : 1;

}new_log_t;

typedef struct

{

unsigned f1 : 1;

unsigned f2 : 1;

unsigned f3 : 1;

unsigned f4 : 1;

unsigned f5 : 1;

unsigned f6 : 1;

unsigned f7 : 1;

unsigned f8 : 1;

unsigned f9 : 1;

unsigned f10 : 1;

unsigned f11 : 1;

unsigned f12 : 1;

unsigned f13 : 1;

unsigned f14 : 1;

unsigned f15 : 1;

unsigned f16 : 1;

unsigned f17 : 1;

unsigned f18: 1;

unsigned f19 : 1;

unsigned f20 : 1;

unsigned f21 : 1;

unsigned f22 : 1;

unsigned f23 : 1;

unsigned f24 : 1;

unsigned f25 : 1;

unsigned f26 : 1;

unsigned f27 : 1;

unsigned f28 : 1;

unsigned f29 : 1;

unsigned f30 : 1;

unsigned f31 : 1;

unsigned f32 : 1;

unsigned f33 : 1;

}new_log_t;sizeof(new_log_t) = 8 ,看一看只有32个成员时候占多少吧

[cpp]

typedef struct

{

unsigned f1 : 1;

unsigned f2 : 1;

unsigned f3 : 1;

unsigned f4 : 1;

unsigned f5 : 1;

unsigned f6 : 1;

unsigned f7 : 1;

unsigned f8 : 1;

unsigned f9 : 1;

unsigned f10 : 1;

unsigned f11 : 1;

unsigned f12 : 1;

unsigned f13 : 1;

unsigned f14 : 1;

unsigned f15 : 1;

unsigned f16 : 1;

unsigned f17 : 1;

unsigned f18: 1;

unsigned f19 : 1;

unsigned f20 : 1;

unsigned f21 : 1;

unsigned f22 : 1;

unsigned f23 : 1;

unsigned f24 : 1;

unsigned f25 : 1;

unsigned f26 : 1;

unsigned f27 : 1;

unsigned f28 : 1;

unsigned f29 : 1;

unsigned f30 : 1;

unsigned f31 : 1;

unsigned f32 : 1;

}new_log_t;

typedef struct

{

unsigned f1 : 1;

unsigned f2 : 1;

unsigned f3 : 1;

unsigned f4 : 1;

unsigned f5 : 1;

unsigned f6 : 1;

unsigned f7 : 1;

unsigned f8 : 1;

unsigned f9 : 1;

unsigned f10 : 1;

unsigned f11 : 1;

unsigned f12 : 1;

unsigned f13 : 1;

unsi

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