在PC和Arduino的C的++的sizeof（）的区别 [英] Sizeof() difference between C++ on PC and Arduino

问题描述

可能重复：
  <一href=\"http://stackoverflow.com/questions/119123/why-isnt-sizeof-for-a-struct-equal-to-the-sum-of-sizeof-of-each-member\">Why为等于每个成员的sizeof的总和一个结构是不是和sizeof？

在以下code，值 structSize 取决于它的上一个Arduino VS我的电脑（Ubuntu的11.04 x64）的执行是不同的。

In the following code, the value of structSize is different depending on whether it's executed on an Arduino vs my PC (Ubuntu 11.04 x64).

struct testStruct{
    uint8_t val1;
    uint16_t val2;
};
...
uint_8_t structSize = sizeof(testStruct);

在我的电脑， structSize 的值是4，和我的Arduino structSize 的值是3 （如预期）。

On my PC, the value of structSize is 4, and on my Arduino the value of structSize is 3 (as expected).

哪里是这4个字节来自哪里？

Where is this 4th byte coming from?

推荐答案

其实，我本来期望的大小为4，因为 uint16_t 通常对准到16位

Actually, I would have expected the size to be 4, because uint16_t is usually aligned to 16 bits.

额外的字节填充插入成员之间保持对齐 uint16_t 。

The extra byte is padding inserted between the members to keep the alignment of uint16_t.

这是编译器相关的，但。 Arduino的可能与内存更自私，可能不会很在乎对齐。 （可能的解释）

This is compiler dependent though. Arduino might be more selfish with memory and probably doesn't care that much about alignment. (possible explanation)

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