將多個變量存儲到memcpy緩衝區

Question

我很新的Arduino和我找不到任何方式來做到以下幾點。 我有一個typedef結構填補了多個值：

void loop() { 
accel.process(); 
AccelerationReading accelData; 
accelData.xAxis = accel.xAxis; 
accelData.yAxis = accel.yAxis; 
accelData.zAxis = accel.zAxis; 
//Irrelevant code after this 
} 

後的結構充滿我memcpy它的緩衝區：

uint8_t buffer[6]; 
memcpy((void*)buffer, (void*)&accelData, 6); 

現在這工作正常，但我還需要讀取值來自兩個模擬端口，這兩個值也需要添加到memcpy中。填充兩個變量的代碼：

//New variables 
int shortflexposition; 
int longflexposition; 
//Filling up the variables. 
shortflexposition = analogRead(shortflexpin); 
longflexposition = analogRead(longflexpin); 

的accelData包含6個字節的原始值的，現在我想以後這些字節添加shortflexposition和longflexposition 。變量shortflexposition和longflexposition中的值總是介於0和1023之間。 我應該如何將這些其他變量添加到memcpy中？我試過例如：

uint8_t buffer[8]; 
memcpy((void*)buffer, (void*)&accelData + shortflexposition, 8); 

但是，這似乎寧願增加價值eachother比將它們添加到下一個字節或東西。那麼，如何使用memcpy在下一個字節位置添加新變量？

謝謝！ Yenthe

更新： 這是從倫丁代碼試圖..

typedef union 
{ 
    struct s 
    { 
    AccelerationReading accelData; 
    uint16_t shortflexposition; 
    uint16_t longflexposition; 
    }; 
uint8_t raw_data [sizeof(struct s)]; 
} my_data; 

void setup() { 
// Bean Serial is at a fixed baud rate. Changing the value in Serial.begin() has no effect. 
Serial.begin(); 
accel.init(); 
} 

void loop() { 
    accel.process(); 
    AccelerationReading accelData; 
    my_data data; 
    data.accelData.xAxis = accel.xAxis; 
    data.accelData.yAxis = accel.yAxis; 
    data.accelData.zAxis = accel.zAxis; 

    //Get flex readings 
    int shortflexposition; 
    int longflexposition; 

    //Read the position of the flex sensor (0 to 1023?) 
    data.shortflexposition = analogRead(shortflexpin); 
    data.longflexposition = analogRead(longflexpin); 
    my_data some_other_data = data; 

    uint8_t buffer[6]; 
    memcpy((void*)buffer, (void*)&accelData, 6); 
    Bean.setScratchData(1,buffer,6); 
    Bean.sleep(1000); 
} 

但給出了以下錯誤：

GetReader.ino: In function 'void loop()': 
GetReader.ino:54:8: error: 'union loop()::my_data' has no member named 'accelData' 
GetReader.ino:55:8: error: 'union loop()::my_data' has no member named 'accelData' 
GetReader.ino:56:8: error: 'union loop()::my_data' has no member named 'accelData' 
GetReader.ino:63:8: error: 'union loop()::my_data' has no member named 'shortflexposition' 
GetReader.ino:64:8: error: 'union loop()::my_data' has no member named 'longflexposition' 

Answer 1

首先，它不如果要添加兩個16位數字== 4個字節，請使用2個字節來增加緩衝區大小。我會建議你做這樣的事情：

typedef union 
{ 
    struct s 
    { 
    AccelerationReading accelData; 
    uint16_t shortflexposition; 
    uint16_t longflexposition; 
    }; 
    uint8_t raw_data [sizeof(struct s)]; 
} my_data; 


// use whatever compile-time assert you have available to check for padding: 
static_assert(sizeof(my_data) == sizeof(AccelerationReading) + 2*sizeof(uint16_t), 
       "Unwanted padding detected."); 


my_data data; 
data.accelData.xAxis = x; 
data.accelData.yAxis = y; 
data.accelData.ZAxis = z; 
data.shortflexposition = something; 
data.longflexposition = something; 

my_data some_other_data = data; // equivalent of memcpy 

如果您需要按字節來訪問數據字節，只需使用data.raw_data[i]代替。

---

如果您使用的是舊的編譯器，你必須將代碼更改爲：

typedef union 
{ 
    struct s 
    { 
    AccelerationReading accelData; 
    uint16_t shortflexposition; 
    uint16_t longflexposition; 
    } my_compiler_is_old; 
    uint8_t raw_data [sizeof(struct s)]; 
} my_data; 

data.my_compiler_is_old.accelData.xAxis = x; 
data.my_compiler_is_old.accelData.yAxis = y; 
...