Build Arduino library

Question

I've tried to build a library (file.cpp + file.h) to Arduino but I got this error:

In file included from EXAMPLE_MPL3115A2.ino:2: /Applications/Arduino.app/Contents/Resources/Java/libraries/MPL3115A2/MPL3115A2.h:8: error: ISO C++ forbids declaration of 'getPressure' with no type EXAMPLE_MPL3115A2.ino: In function 'void loop()': EXAMPLE_MPL3115A2:18: error: expected unqualified-id before '.' token

Can you explain me where is the error?? (I don't know very well C++)

Here are my MPL3115A2.h

#ifndef MPL3115A2_h
#define MPL3115A2_h
#include "Arduino.h"
class MPL3115A2{
public:
 getPressure();
private:
 int m_i2c_address;
 byte _p_msb, _p_csb, _plsb;
 byte _tempp, _tempa, _tempt, _decimalPress, _decimalAlt, _decimalTemp;
 unsigned long _ptot;
};
#endif 

my MPL3115A2.cpp

#include "Arduino.h"
#include "MPL3115A2.h"
#include "I2C.h"
MPL3115A2::MPL3115A2()
{
 m_i2c_address = 0x60;
 p_msb = _p_msb;
 p_csb = _p_csb;
 p_lsb = _p_lsb;
 tempp = _tempp;
 tempa = _tempa;
 tempt = _tempt;
 decimalPress = _decimalPress;
 decimalAlt = _decimalAlt;
 decimalTemp = _decimalTemp;
 ptot = _ptot;
}
float MPL3115A2::getPressure()
{
 I2c.write(m_i2c_address,0x26,0x00);
 I2c.write(m_i2c_address,0x26,0x01); 
 delay(100);
 I2c.read(m_i2c_address,0x1,3);
 I2c.end();
 while(I2c.available()){
 p_msb=I2c.receive(); 
 p_csb=I2c.receive(); 
 p_lsb=I2c.receive();}
 ptot=p_msb;
 ptot=(ptot<<8)+p_csb;
 ptot=(ptot<<2)+(p_lsb>>6);
 tempp=(p_lsb<<2);
 if(tempp==192){
 decimalPress=75;
 }else if(tempp==128){
 decimalPress=25;
 }else if(tempp==64){
 decimalPress=5;
 }else{tempp=0;}
 Serial.print(ptot);
 Serial.print(".");
 Serial.println(decimalPress);
}
#endif

and my example.pde

#include <Arduino.h>
#include <MPL3115A2.h>
#include <I2C.h>
void setup(){
 Serial.begin(9600);
 I2c.begin();
}
//LOOP
void loop(){
 Serial.print("Pressure is: ");
 MPL3115A2.getPressure(); //Expressed in Pa
 Serial.print("Altimetry is: ");
 //MPL3115A2.getAltimetry(); //Expressed in m
 Serial.print("Temperature is: ");
 // MPL3115A2.getTemperature(); //Expressed in C
 delay(2000);
}

Sorry for the long post! Thank you all for your help!

• spring: down vote cowards need to post their reason

Answer 1

getPressure() has no return type! According to the cpp you posted, your header file should declare the method as float getPressure(); so change your header file to:

#ifndef MPL3115A2_h
#define MPL3115A2_h
#include "Arduino.h"
class MPL3115A2{
public:
 float getPressure(); // <- only change here
private:
 int m_i2c_address;
 byte _p_msb, _p_csb, _plsb;
 byte _tempp, _tempa, _tempt, _decimalPress, _decimalAlt, _decimalTemp;
 unsigned long _ptot;
};
#endif 

to correspond with the definition which is

float MPL3115A2::getPressure()
{
 // your processing code...
}

Also, keep in mind that you should review your constructor as it is not declared in your header. Also, doing something like

p_msb = _p_msb;
p_csb = _p_csb;
p_lsb = _p_lsb;
tempp = _tempp;
tempa = _tempa;
tempt = _tempt;
decimalPress = _decimalPress;
decimalAlt = _decimalAlt;
decimalTemp = _decimalTemp;
ptot = _ptot;

is really weird. What are the variables on the left? You are initializing them with your uninitialized members (those on the right, starting with _). You should consider giving an initial value to these members (like 0?)

Changing your constructor to something like:

MPL3115A2::MPL3115A2()
{
 _p_msb = 0;
 _p_csb = 0;
 _p_lsb = 0;
 _tempp = 0;
 _tempa = 0;
 _tempt = 0;
 _decimalPress = 0;
 _decimalAlt = 0;
 _decimalTemp = 0;
 _ptot = 0;
}

To make sure your member variables are initialized with a "known" value.

Also, most of these values seem temporary (you might not need them outside of a call to getPressure(). In this case, consider moving all these bytes to the scope of the function instead of inside the sensor class to avoid using unnecessary memory - there is not that much available on Arduinos.

You will also need to add MPL3115A2(); in the public part of your MPL3115A2 class, this is because you are defining a body for this constructor in the CPP file, therefore you need to declare it so that it's part of the object.

• Anders R. Bystrup: Or actually float MPL3115A2::getPressure() as can be seen in MPL3115A2.cppabove :-)
• Caribou: @emartel you were right of course - I deleted the answer - was distracted
• emartel: @8bit_Biker for example, your constructor assings ptot with _ptot. In the code you provided, ptot doesn't exist and _ptot wasn't given an initial value yet!
• 8bit_Biker: Sorry but I don't understand your advice. These are "temp" vars corresponding to the pressure/altitude/etc sensor's register (pressure most significant byte... and so on), so I thought to consider them as temporary variable. But you must consider I'm far for being a programmer!So, I really appreciate if you could show me how it is the most correct way to use it
• emartel: @8bit_Biker you probably just need to add MPL3115A2(); right before your float getPressure(); in your header file to declare that you will be providing a constructor :)

Answer 2

I'm thinking that the getPressure() method should be declared with the return type float as you implement it in MPL3115A2.cpp, so the 'h file should have:

...
class MPL3115A2 {
 public:
 float getPressure();
 // (and remember the constructor)
 private: 
 ...
}

Also, are you aware that the method doesn't actually return anything? If that is the idea, you could make it a void getPressure() and change the class definition accordingly.

Added: For future readers, the answer is available in the error message, albeit well hidden in cryptic stuff: "...ISO C++ forbids declaration of 'getPressure' with no type..."

Hope that helps.