挥发性结构体语义学 [英] Volatile Struct Semantics

问题描述

是否足以声明结构类型的变量的一个实例挥发性（如果字段在重入code访问），或者必须在一个声明结构的特定字段挥发性？

Is it sufficient to declare an instance of a structure-typed variable as volatile (if its fields are accessed in re-entrant code), or must one declare specific fields of the structure as volatile?

来表述不同，有什么之间的语义差别（如果有的话）：

Phrased differently, what are the semantic differences (if any) between:

typdef struct {
  uint8_t bar;
} foo_t;

volatile foo_t foo_inst;

和

typedef struct{
  volatile uint8_t bar;
} foo_t;

foo_t foo_inst;

我承认，声明指针类型的变量挥发性（例如挥发性uint8_t有* foo的）只是通知的地址指向的由富可能会改变，同时使没有语句有关值由富指向的编译器。目前还不清楚我的比喻是否适用于结构类型的变量。

I recognize that declaring a pointer-typed variable as volatile (e.g. volatile uint8_t * foo) merely informs the compiler that the address pointed-to by foo may change, while making no statement about the values pointed to by foo. It is unclear to me whether an analogy holds for structure-typed variables.

推荐答案

在你的榜样，两者是相同的。但是，问题围绕指针。

In your example, the two are the same. But the issues revolve around pointers.

首先，挥发性uint8_t有* foo的; 告诉编译器内存被指向的波动。如果你想标记指针本身挥发性，你需要做的 uint8_t有* foo的波动;

First off, volatile uint8_t *foo; tells the compiler the memory being pointed to is volatile. If you want to mark the pointer itself as volatile, you would need to do uint8_t * volatile foo;

这就是你在哪里得到标记结构作为挥发性VS标记单个字段三者之间的主要差异。如果你有：

And that is where you get to the main differences between marking the struct as volatile vs marking individual fields. If you had:

typedef struct
{
    uint8_t *field;
} foo;

volatile foo f;

这会像：

typedef struct
{
    uint8_t * volatile field;
} foo;

和不喜欢的：

typedef struct
{
    volatile uint8_t *field;
} foo;

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