[英]indexing an element from a volatile struct doesn't work in C++
I have this code:我有这个代码:
typedef struct {
int test;
} SensorData_t;
volatile SensorData_t sensorData[10];
SensorData_t getNextSensorData(int i)
{
SensorData_t data = sensorData[i];
return data;
}
int main(int argc, char** argv) {
}
It compiles with gcc version 8.3, but not with g++.它可以用 gcc 8.3 版编译,但不能用 g++ 编译。 Error message:
错误信息:
main.c: In function ‘SensorData_t getNextSensorData(int)’:
main.c:8:34: error: no matching function for call to ‘SensorData_t(volatile SensorData_t&)’
SensorData_t data = sensorData[i];
^
main.c:3:3: note: candidate: ‘constexpr SensorData_t::SensorData_t(const SensorData_t&)’ <near match>
} SensorData_t;
^~~~~~~~~~~~
main.c:3:3: note: conversion of argument 1 would be ill-formed:
main.c:8:34: error: binding reference of type ‘const SensorData_t&’ to ‘volatile SensorData_t’ discards qualifiers
SensorData_t data = sensorData[i];
~~~~~~~~~~~~^
main.c:3:3: note: candidate: ‘constexpr SensorData_t::SensorData_t(SensorData_t&&)’ <near match>
} SensorData_t;
^~~~~~~~~~~~
main.c:3:3: note: conversion of argument 1 would be ill-formed:
main.c:8:34: error: cannot bind rvalue reference of type ‘SensorData_t&&’ to lvalue of type ‘volatile SensorData_t’
SensorData_t data = sensorData[i];
I'm not sure if I need to add volatile as well for the data
variable and the return type, shouldn't be needed because it is copied.我不确定是否需要为
data
变量和返回类型添加 volatile,因为它是复制的,所以不需要。 But I do access the sensorData array from an interrupt as well (on an embedded system), so I think I need volatile
for the top level variable sensorData.但是我也确实从中断(在嵌入式系统上)访问了 sensorData 数组,所以我认为我需要
volatile
用于顶级变量 sensorData。
Your program is trying to copy a SensorData_t
object.您的程序正在尝试复制
SensorData_t
对象。 The compiler supplies a copy constructor with the following signature:编译器提供具有以下签名的复制构造函数:
SensorData_t(const SensorData_t &)
This copy constructor will not work with volatile
arguments, hence the compilation error.此复制构造函数不适用于
volatile
参数,因此会出现编译错误。
You can write your own copy constructor which works with volatile
SensorData_t
objects (as well as non- volatile
SensorData_t
objects):您可以编写自己的复制构造函数,它适用于
volatile
SensorData_t
对象(以及volatile
SensorData_t
对象):
struct SensorData_t {
SensorData_t() = default;
SensorData_t(const volatile SensorData_t &other)
: test(other.test) {
}
int test;
};
As an alternative to the accepted answer, you may consider avoid copying the data from the array altogether, if the getNextSensorData
is a simple getter function for the global sensorData
:作为已接受答案的替代方案,如果
getNextSensorData
是全局sensorData
的简单getter函数,您可以考虑完全避免从数组中复制数据:
// Intorduce type alias
using SD = const volatile SensorData_t&;
SD getNextSensorData(int i)
{
return sensorData[i];
}
This way (if it is suitable for the design), you'll keep the definitions code more concise.这样(如果它适合设计),您将保持定义代码更简洁。 But I have to note that the usage is a bit less direct than in the copy case:
但我必须注意,它的用法比在复制情况下要不那么直接:
int main() {
// Type alias
SD sd1 = getNextSensorData(0);
// Deduced type
auto&& sd2 = getNextSensorData(1);
// Explicit type
const volatile SensorData_t& sd3 = getNextSensorData(2);
}
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