警告:返回一个值的语句，在函数返回'void‘[-fpermissive]返回高度；

Question

我对arduino很陌生，我不知道为什么会出现这个错误。任何帮助都将不胜感激。上述错误出现在设置函数中。我对功能还没有太大的经验，因为我只是在几个星期前才开始研究这些功能。

#include <Adafruit_BMP280.h> // For the purple BMP280 sensor board
#include <SoftwareSerial.h>


// Purple BMP280 Sensor Board
Adafruit_BMP280 bmp; //use I2C interface 
Adafruit_Sensor *bmp_temp = bmp.getTemperatureSensor();
Adafruit_Sensor *bmp_pressure = bmp.getPressureSensor();

float temp;
float pressure;
float calculate_altitude(float temp, float pressure);
float altitude;
float altitude1;
float altitude2;
float altitude3;
float x;
float y;
float z;

  // Initialising variables


void setup() {
  //Setup for purple BMP280
 Serial.begin(300);
 
Serial.println(F("BMP280 Sensor event test"));

if (!bmp.begin()) {
  Serial.println(F("Could not find a valid BMP280 sensor, check wiring!"));
  while (1) delay(10);
}

//Default settings from datasheet
bmp.setSampling(Adafruit_BMP280::MODE_NORMAL, //Opertaing Mode
Adafruit_BMP280::SAMPLING_X2, //Temp. oversampling
Adafruit_BMP280::SAMPLING_X16, //Pressure oversampling
Adafruit_BMP280::FILTER_X16, //Filtering
Adafruit_BMP280::STANDBY_MS_500); //Standby time

bmp_temp->printSensorDetails();


 //Calculation for altitude using temperature and pressure values
float calculate_altitude(float temp, float pressure);
{
 float altitude;
 
altitude1 = 1013.25/(pressure);
altitude2 = pow(altitude1,0.190222560);
altitude3 = altitude2-1;
altitude = (altitude3*(temp +273.15))/0.0065;

return altitude;
}
}
void loop() {

  //Obtaining temperature and pressure events off BMP280
sensors_event_t temp_event, pres_event;
bmp_temp->getEvent(&temp_event);
bmp_pressure->getEvent(&pres_event);

//Taking temperature and pressure values from the events
temp = temp_event.temperature;
pressure = pres_event.pressure;

altitude = calculate_altitude(temp, pressure);



//Reading acceleration values in X, Y and Z axis directions from accelerometer
x = analogRead(A1);
y = analogRead(A2);
z = analogRead(A3);

  Serial.print(" temperature = ");
  Serial.print(temp); //Print temperature value
  Serial.print(",");
    Serial.print(" pressure = ");
  Serial.print(pressure); //Print pressure value
  Serial.print(",");
    Serial.print(" altitude = ");
  Serial.print(altitude); //Read altitude value
  Serial.print(",");
    Serial.print(" x axis acceleration = ");
  Serial.print(x);  //Read acceleration in X direction
  Serial.print(",");
  Serial.print(" y axis acceleration = ");
   Serial.print(y);  //Read acceleration in Y direction
  Serial.print(",");
  Serial.print(" z axis acceleration = ");
  Serial.println(z); //Read acceleration in Z direction
 delay(100);
}

我还在循环函数中得到这个错误:对`calculate_altitude(float，float)‘的未定义引用。如果这一点可以解释的话，我就不明白它意味着什么，也不明白如何解决这个问题。

Answer 1

根据C标准(6.8.6.4返回声明)

带表达式的返回语句不应出现在返回类型为

的函数中。没有表达式的返回语句只能出现在返回类型为whose的函数中。

函数setup声明为返回类型void，它有一个带有表达式的返回语句。

void setup() {
  //...
 //Calculation for altitude using temperature and pressure values
float calculate_altitude(float temp, float pressure);
{
 float altitude;
 
altitude1 = 1013.25/(pressure);
altitude2 = pow(altitude1,0.190222560);
altitude3 = altitude2-1;
altitude = (altitude3*(temp +273.15))/0.0065;

return altitude;
}
}

这似乎是一个错误的结果。似乎您正在尝试定义函数calculate_altitude，并错误地将其放置在函数setup中。但是由于分号

float calculate_altitude(float temp, float pressure);
                                                   ^^^

编译器将其视为块作用域函数声明，因此返回语句属于函数setup，而不是函数calculate_altitude。

这种错误的原因是错误的代码格式。

Answer 2

有了正确的缩进和我在上面的注释中描述的更正，您的代码应该是这样的：

#include <Adafruit_BMP280.h> // For the purple BMP280 sensor board
#include <SoftwareSerial.h>

// Purple BMP280 Sensor Board
Adafruit_BMP280 bmp; //use I2C interface 
Adafruit_Sensor *bmp_temp = bmp.getTemperatureSensor();
Adafruit_Sensor *bmp_pressure = bmp.getPressureSensor();

float temp;
float pressure;
float calculate_altitude(float temp, float pressure);
float altitude;
float altitude1;
float altitude2;
float altitude3;
float x;
float y;
float z;

  // Initialising variables
void setup()
{
    //Setup for purple BMP280
    Serial.begin(300);
    Serial.println(F("BMP280 Sensor event test"));
    if (!bmp.begin()) {
        Serial.println(F("Could not find a valid BMP280 sensor, check wiring!"));
        while (1) delay(10);
    }
} // this close-brace was missing

//Default settings from datasheet
bmp.setSampling(Adafruit_BMP280::MODE_NORMAL, //Opertaing Mode
Adafruit_BMP280::SAMPLING_X2, //Temp. oversampling
Adafruit_BMP280::SAMPLING_X16, //Pressure oversampling
Adafruit_BMP280::FILTER_X16, //Filtering
Adafruit_BMP280::STANDBY_MS_500); //Standby time

bmp_temp->printSensorDetails();

//Calculation for altitude using temperature and pressure values
float calculate_altitude(float temp, float pressure)  //; - Extra semicolon
{
    float altitude;
 
    altitude1 = 1013.25/(pressure);
    altitude2 = pow(altitude1,0.190222560);
    altitude3 = altitude2-1;
    altitude = (altitude3*(temp +273.15))/0.0065;
    return altitude;
}

// }这里有特制的紧支撑

void loop() {

    //Obtaining temperature and pressure events off BMP280
    sensors_event_t temp_event, pres_event;
    bmp_temp->getEvent(&temp_event);
    bmp_pressure->getEvent(&pres_event);

    //Taking temperature and pressure values from the events
    temp = temp_event.temperature;
    pressure = pres_event.pressure;

    altitude = calculate_altitude(temp, pressure);

    //Reading acceleration values in X, Y and Z axis directions from accelerometer
    x = analogRead(A1);
    y = analogRead(A2);
    z = analogRead(A3);
    Serial.print(" temperature = ");
    Serial.print(temp); //Print temperature value
    Serial.print(",");
    Serial.print(" pressure = ");
    Serial.print(pressure); //Print pressure value
    Serial.print(",");
    Serial.print(" altitude = ");
    Serial.print(altitude); //Read altitude value
    Serial.print(",");
    Serial.print(" x axis acceleration = ");
    Serial.print(x);  //Read acceleration in X direction
    Serial.print(",");
    Serial.print(" y axis acceleration = ");
    Serial.print(y);  //Read acceleration in Y direction
    Serial.print(",");
    Serial.print(" z axis acceleration = ");
    Serial.println(z); //Read acceleration in Z direction
    delay(100);
}

(请注意，我没有Arduino，因此无法为您测试编译此代码。)但我纠正了明显的错误。