warning: return-statement with a value, in function returning 'void' [-fpermissive] return-CodePudding

I'm new to arduino and I dont know why this error is coming up. Any help would be greatly appreciated. The above error is in the set up function. I am not too experienced with functions yet as I have only began working on them a couple of weeks ago.

#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);
}

I am also getting this error in the loop function: undefined reference to `calculate_altitude(float, float)'. If this could be explained aswell I dont understand what it means and what to do to solve it.

CodePudding user response：

According to the C Standard (6.8.6.4 The return statement)

1 A return statement with an expression shall not appear in a function whose return type is void. A return statement without an expression shall only appear in a function whose return type is void.

Your function setup declared with the return type void has a return statement with an expression.

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;
}
}

It seems it is a result of a typo. It seems you are trying to define the function calculate_altitude and by mistake placed it within the function setup. But due to semicolons

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

the compiler considers it as a block scope function declaration and as a result the return statement belongs to the function setup instead of to the function calculate_altitude.

The reason of such a typo is a bad code formatting.

CodePudding user response：

With proper indenting and the corrections I described in my comment above, this is how your code should look:

#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;
}

// } Extra close-brace here

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);
}

(Note that I do not have an Arduino so was unable to test compile this code for you.) But I corrected the obvious errors.