Cannot declare variable to be of abstract type ошибка

EDIT: After spending a bit of time understanding the code I wrote I still don’t know what is wrong with it. This is the base class from which I derived my class:

///ContactResultCallback is used to report contact points
struct  ContactResultCallback
{
    short int   m_collisionFilterGroup;
    short int   m_collisionFilterMask;

    ContactResultCallback()
        :m_collisionFilterGroup(btBroadphaseProxy::DefaultFilter),
        m_collisionFilterMask(btBroadphaseProxy::AllFilter)
    {
    }

    virtual ~ContactResultCallback()
    {
    }

    virtual bool needsCollision(btBroadphaseProxy* proxy0) const
    {
        bool collides = (proxy0->m_collisionFilterGroup & m_collisionFilterMask) != 0;
        collides = collides && (m_collisionFilterGroup & proxy0->m_collisionFilterMask);
        return collides;
    }

    virtual btScalar    addSingleResult(btManifoldPoint& cp,    const btCollisionObjectWrapper* colObj0Wrap,int partId0,int index0,const btCollisionObjectWrapper* colObj1Wrap,int partId1,int index1) = 0;
};

Now here is my derived class:

class DisablePairCollision : public btCollisionWorld::ContactResultCallback
{
public:
    virtual btScalar addSingleResult(btManifoldPoint& cp, const btCollisionObject* colObj0, int32_t partId0, int32_t index0, const btCollisionObject* colObj1, int32_t partId1, int32_t index1);

    btDiscreteDynamicsWorld* DynamicsWorld;
};

And below is where I implement the main function. Still not sure why I’m getting this error.

I was using the code below on windows with both vc2010 and code blocks without a problem:

btScalar DisablePairCollision::addSingleResult(btManifoldPoint& cp, const btCollisionObject* colObj0, int32_t partId0, int32_t index0, const btCollisionObject* colObj1, int32_t partId1, int32_t index1)
{
    // Create an identity matrix.
    btTransform frame;
    frame.setIdentity();

    // Create a constraint between the two bone shapes which are contacting each other.
    btGeneric6DofConstraint* Constraint;
    Constraint = new btGeneric6DofConstraint( *(btRigidBody*)colObj0, *(btRigidBody*)colObj1, frame, frame, true );

    // Set limits to be limitless.
    Constraint->setLinearLowerLimit( btVector3(1, 1, 1 ) );
    Constraint->setLinearUpperLimit( btVector3(0, 0, 0 ) );
    Constraint->setAngularLowerLimit( btVector3(1, 1, 1 ) );
    Constraint->setAngularUpperLimit( btVector3(0, 0, 0 ) );

    // Add constraint to scene.
    DynamicsWorld->addConstraint(Constraint, true);
    return 0;
}

Now I’m trying to compile my project on Ubuntu but I am getting this error when I try to use that class:

/home/steven/Desktop/ovgl/src/OvglScene.cpp:211: error: cannot declare variable ‘Callback’ to be of abstract type ‘Ovgl::DisablePairCollision’

error: cannot declare variable 'b' to be of abstract type 'B'
note: because the following virtual functions are pure within 'B'
note: virtual bool Serializable::eq(const QString&) const
virtual bool eq( const QString & qs) const = 0;
^
note: virtual bool Serializable::eq(const Serializable*) const
virtual bool eq( const Serializable * o) const = 0;
^

class Serializable {
public:
virtual  bool eq( const QString & qs) const = 0;
virtual  bool eq( const Serializable * o) const = 0;
};

class JSONSerializable : public Serializable {
public:
virtual  QString toJSON( void) const = 0;

virtual  bool eq( const QString & qs) const {
return toJSON() == qs;
}
virtual  bool eq( const Serializable * o) const {
return eq( (( JSONSerializable *) o)->toJSON());
}
};

class A : public Serializable {  };

class B : public A,
public JSONSerializable {
public:
virtual  QString toJSON( void) const {
return QString( "test!");
}
};

…
B b;
qDebug() << b.toJSON();
…

Решение

class Serializable {
public:
virtual  bool eq( const QString & qs) const = 0;
virtual  bool eq( const Serializable * o) const = 0;
};

class JSONSerializable : virtual public Serializable {
public:
virtual  QString toJSON( void) const = 0;

virtual  bool eq( const string & qs) const {
return toJSON() == qs;
}
virtual  bool eq( const Serializable * o) const {
return eq(dynamic_cast<const JSONSerializable*>(o)->toJSON());
}
};

class A : virtual public Serializable {  };

class B : virtual public A,
public JSONSerializable {
public:
virtual  QString toJSON( void) const {
return QString( "test!");
}
};

Другие решения

РЕДАКТИРОВАТЬ: Потратив немного времени на понимание кода, который я написал, я до сих пор не знаю, что с ним не так. Это базовый класс, из которого я получил свой класс:

///ContactResultCallback is used to report contact points
struct  ContactResultCallback
{
    short int   m_collisionFilterGroup;
    short int   m_collisionFilterMask;

    ContactResultCallback()
        :m_collisionFilterGroup(btBroadphaseProxy::DefaultFilter),
        m_collisionFilterMask(btBroadphaseProxy::AllFilter)
    {
    }

    virtual ~ContactResultCallback()
    {
    }

    virtual bool needsCollision(btBroadphaseProxy* proxy0) const
    {
        bool collides = (proxy0->m_collisionFilterGroup & m_collisionFilterMask) != 0;
        collides = collides && (m_collisionFilterGroup & proxy0->m_collisionFilterMask);
        return collides;
    }

    virtual btScalar    addSingleResult(btManifoldPoint& cp,    const btCollisionObjectWrapper* colObj0Wrap,int partId0,int index0,const btCollisionObjectWrapper* colObj1Wrap,int partId1,int index1) = 0;
};

Теперь вот мой производный класс:

class DisablePairCollision : public btCollisionWorld::ContactResultCallback
{
public:
    virtual btScalar addSingleResult(btManifoldPoint& cp, const btCollisionObject* colObj0, int32_t partId0, int32_t index0, const btCollisionObject* colObj1, int32_t partId1, int32_t index1);

    btDiscreteDynamicsWorld* DynamicsWorld;
};

А ниже я реализую основную функцию. Все еще не уверен, почему я получаю эту ошибку.

Я без проблем использовал приведенный ниже код в окнах как с vc2010, так и с кодовыми блоками:

btScalar DisablePairCollision::addSingleResult(btManifoldPoint& cp, const btCollisionObject* colObj0, int32_t partId0, int32_t index0, const btCollisionObject* colObj1, int32_t partId1, int32_t index1)
{
    // Create an identity matrix.
    btTransform frame;
    frame.setIdentity();

    // Create a constraint between the two bone shapes which are contacting each other.
    btGeneric6DofConstraint* Constraint;
    Constraint = new btGeneric6DofConstraint( *(btRigidBody*)colObj0, *(btRigidBody*)colObj1, frame, frame, true );

    // Set limits to be limitless.
    Constraint->setLinearLowerLimit( btVector3(1, 1, 1 ) );
    Constraint->setLinearUpperLimit( btVector3(0, 0, 0 ) );
    Constraint->setAngularLowerLimit( btVector3(1, 1, 1 ) );
    Constraint->setAngularUpperLimit( btVector3(0, 0, 0 ) );

    // Add constraint to scene.
    DynamicsWorld->addConstraint(Constraint, true);
    return 0;
}

Теперь я пытаюсь скомпилировать свой проект в Ubuntu, но получаю эту ошибку, когда пытаюсь использовать этот класс:

/home/steven/Desktop/ovgl/src/OvglScene.cpp:211: error: cannot declare variable ‘Callback’ to be of abstract type ‘Ovgl::DisablePairCollision’

Hi Rui,
Yes the WiFi scan example compiles fine (in fact the ESP32 is more sensitive than the WiFi on my phone!)
Indeed everything in the corse so far has been fine until the web server display sensor readings sketch, and I actually have a real world use for this to monitor the temp and humidity in our greenhouse..
I have pasted the code below directly from the Arduino IDE:
/*********
Rui Santos
Complete project details at http://randomnerdtutorials.com
*********/
// Load Wi-Fi library
#include <WiFi.h>
#include <Wire.h>
#include <Adafruit_BME280.h>
#include <Adafruit_Sensor.h>
//uncomment the following lines if you’re using SPI
/*#include <SPI.h>
#define BME_SCK 18
#define BME_MISO 19
#define BME_MOSI 23
#define BME_CS 5*/
#define SEALEVELPRESSURE_HPA (1013.25)
Adafruit_BME280 bme; // I2C
//Adafruit_BME280 bme(BME_CS); // hardware SPI
//Adafruit_BME280 bme(BME_CS, BME_MOSI, BME_MISO, BME_SCK); // software SPI
// Replace with your network credentials
const char* ssid = “SSID”;
const char* password = “password”;
// Set web server port number to 80
WiFiServer server(80);
// Variable to store the HTTP request
String header;
void setup() {
Serial.begin(115200);
bool status;
// default settings
// (you can also pass in a Wire library object like &Wire2)
//status = bme.begin();
if (!bme.begin(0x76)) {
Serial.println(“Could not find a valid BME280 sensor, check wiring!”);
while (1);
}
// Connect to Wi-Fi network with SSID and password
Serial.print(“Connecting to “);
Serial.println(ssid);
WiFi.begin(ssid, password);
while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(“.”);
}
// Print local IP address and start web server
Serial.println(“”);
Serial.println(“WiFi connected.”);
Serial.println(“IP address: “);
Serial.println(WiFi.localIP());
server.begin();
}
void loop(){
WiFiClient client = server.available(); // Listen for incoming clients
if (client) { // If a new client connects,
Serial.println(“New Client.”); // print a message out in the serial port
String currentLine = “”; // make a String to hold incoming data from the client
while (client.connected()) { // loop while the client’s connected
if (client.available()) { // if there’s bytes to read from the client,
char c = client.read(); // read a byte, then
Serial.write(c); // print it out the serial monitor
header += c;
if (c == ‘n’) { // if the byte is a newline character
// if the current line is blank, you got two newline characters in a row.
// that’s the end of the client HTTP request, so send a response:
if (currentLine.length() == 0) {
// HTTP headers always start with a response code (e.g. HTTP/1.1 200 OK)
// and a content-type so the client knows what’s coming, then a blank line:
client.println(“HTTP/1.1 200 OK”);
client.println(“Content-type:text/html”);
client.println(“Connection: close”);
client.println();

// Display the HTML web page
client.println(“<!DOCTYPE html><html>”);
client.println(“<head><meta name=”viewport” content=”width=device-width, initial-scale=1”>”);
client.println(“<link rel=”icon” href=”data:,”>”);
// CSS to style the table
client.println(“<style>body { text-align: center; font-family: ”Trebuchet MS”, Arial;}”);
client.println(“table { border-collapse: collapse; width:35%; margin-left:auto; margin-right:auto; }”);
client.println(“th { padding: 12px; background-color: #0043af; color: white; }”);
client.println(“tr { border: 1px solid #ddd; padding: 12px; }”);
client.println(“tr:hover { background-color: #bcbcbc; }”);
client.println(“td { border: none; padding: 12px; }”);
client.println(“.sensor { color:white; font-weight: bold; background-color: #bcbcbc; padding: 1px; }”);

// Web Page Heading
client.println(“</style></head><body><h1>ESP32 with BME280</h1>”);
client.println(“<table><tr><th>MEASUREMENT</th><th>VALUE</th></tr>”);
client.println(“<tr><td>Temp. Celsius</td><td><span class=”sensor”>”);
client.println(bme.readTemperature());
client.println(” *C</span></td></tr>”);
client.println(“<tr><td>Temp. Fahrenheit</td><td><span class=”sensor”>”);
client.println(1.8 * bme.readTemperature() + 32);
client.println(” *F</span></td></tr>”);
client.println(“<tr><td>Pressure</td><td><span class=”sensor”>”);
client.println(bme.readPressure() / 100.0F);
client.println(” hPa</span></td></tr>”);
client.println(“<tr><td>Approx. Altitude</td><td><span class=”sensor”>”);
client.println(bme.readAltitude(SEALEVELPRESSURE_HPA));
client.println(” m</span></td></tr>”);
client.println(“<tr><td>Humidity</td><td><span class=”sensor”>”);
client.println(bme.readHumidity());
client.println(” %</span></td></tr>”);
client.println(“</body></html>”);

// The HTTP response ends with another blank line
client.println();
// Break out of the while loop
break;
} else { // if you got a newline, then clear currentLine
currentLine = “”;
}
} else if (c != ‘r’) { // if you got anything else but a carriage return character,
currentLine += c; // add it to the end of the currentLine
}
}
}
// Clear the header variable
header = “”;
// Close the connection
client.stop();
Serial.println(“Client disconnected.”);
Serial.println(“”);
}
}