C++ references

 C++  No Responses »
Aug 062009
 

Assigning reference return value to a variable

When assigning a reference return value to a variable, a copy is made. Here is an example:

class References {
private:
    std::string name;

public:
    References(const std::string& name) : name(name) {
    };

    virtual ~References() {
    };

    const std::string& getName() const {
        return name;
    };
};

References r("foo");
std::string n = r.getName();

This code makes a copy of the name member variable from the References class and puts the copy into the variable n.

Assigning reference return value to a reference variable

When assigning a reference return value to a reference variable, no copy is made. Here is an example:

class References {
private:
    std::string name;

public:
    References(const std::string& name) : name(name) {
    };

    virtual ~References() {
    };

    const std::string& getName() const {
        return name;
    };
};

References r("foo");
const std::string& n = r.getName();

This code does not make a copy of the name member variable. Instead, the reference variable is now a reference directly to the member variable inside the class.

Passing a reference return value to a method that takes a reference

When you pass the return value from a method that returns a reference directly into a method that takes a reference, no copy is made. Here is an example:

class References {
private:
    std::string name;

public:
    References(const std::string& name) : name(name) {
    };

    virtual ~References() {
    };

    const std::string& getName() const {
        return name;
    };
};

void print(const std::string& s) {
    ...;
}

References r("foo");
print(r.getName());

This passes the reference returned directly into the method as a reference. Therefore, no copy is made.

Using a reference method in a comparison operator

This is the same as the method invocation example above because all operators take references.

Getting the current system time in milliseconds with C++

 C++, Linux, Microsoft, OS X  7 Responses »
Jan 052009
 

After doing quite a bit of C++ recently, I thought I would post my method for getting the current system time in milliseconds in C++ for both Mac OS X and Windows. The Mac version might translate to other Unix platforms, but you’ll have to check the docs or man pages.

Mac OS X

#include <sys/time.h>
timeval time;
gettimeofday(&time, NULL);
long millis = (time.tv_sec * 1000) + (time.tv_usec / 1000);

This actually returns a struct that has microsecond precision.

Windows

#include "windows.h"
SYSTEMTIME time;
GetSystemTime(&time);
WORD millis = (time.wSeconds * 1000) + time.wMilliseconds;

This code gives the milliseconds within the last minute. If you want milliseconds since epoch or some other fixed point in time it will require a bit more math on the SYSTEMTIME struct.

Writing a marker interface in C++

 C++  1 Response »
Dec 092008
 

Just figured this out and it caused me about 3 hours of pain, so I figured I’d post it in case I need to do it again.

class Base {
public:
  virtual ~Base() {};
};

class Derived : public Base {
private:
  set someSet;
public:
  virtual ~Derived() {};
  set getSomeSet() { return someSet; };
};

You might find this necessary if you have some code like this:

class Base {
};

class Derived : public Base {
private:
  set someSet;
public:
  set getSomeSet() { return someSet; };
}

void main() {
  map objects;
  Base base;
  if (objects.find("foo") != objects.end()) {
    base = objects.find("foo")->second; // This is actually a Derived
  }
}

void useBase(Base& base) {
  Derived* derived = (Derived*) &base;
  set someSet = derived->getSomeSet();
  ...
}

This code will toss strange errors such as EXC_BAD_ACCESS and other kernel alarms. I’m not certain way this happens, but I think it is because Derived in the second example isn’t actually an instance of Base since the compiler doesn’t understand that Base is polymorphic. If you try to apply a dynamic_cast operator rather than the pointer cast (as used in example #2) the compiler will complain. What is probably happening is that at runtime the memory for the Derived is not correct because it was cast to a Base, and the kernel freaks out when you attempt to access something in Derived.

Another classic example of C++’s power causing major issues at runtime. These types of problems are not only tricky to figure out, but really only make sense to the kernel and compiler and aren’t obvious from a OO perspective.

Most modern OO languages would have absolutely no issues with the above code, and all dynamic OO languages wouldn’t even need the casts at all and would duck type the invocations via dynamic method invocation.

Visual Studio sucks, NetBeans is coming along, IJ is slipping

 C++, IntelliJ, Java, Visual Studio  3 Responses »
Dec 052008
 

I’ve been working on a decent sized C++ project recently and since the application will be used on a Windows server, I wanted to stay close to that platform. I fired up the latest Visual Studio 2008 version hot off the presses with my MSDN subscription and boy is that thing a piece of junk. It is like working in the stone ages. I mean writing C++ is bad enough and then I have to battle with the worse IDE imaginable?

I think not.

So, I grabbed Eclipse and NetBeans and fired both up. Eclipse, is a beast and I wanted to avoid it at all costs if possible. I’ve never liked Eclipse, no matter the version, and they haven’t improved the issues enough for me to really use it for Java development. However, I found the Eclipse C++ integration decent, but still pretty rough. The Eclipse interface is so clunky that it makes it hard to be productive.

Next I grabbed the latest NetBeans (6.5) and fired it up. I have to say that it started pretty darn fast for a Java IDE. It also has a really decent layout and configuration system. The C++ support, although experimental for on the fly error highlighting, is impressive. After tweaking my colors and battling through keymappings I’m actually productive. NetBeans lacks a number of editor features that are required these days, including multiple clipboards, duplicate lines (has this but no keyboard shortcut), join lines, etc. Besides this problems, I like it.

On the flip side, IntelliJ is still great. 8.0 is just out and it adds a number of new great features and more language support. However, I think that IJ is probably getting close to needing a good chunk rewritten. The configuration system is becoming clunky, the projects difficult to manage, and most aspects of the IDE are beginning to fail.

The speed is horrible, the memory consumption off the charts and the productivity increases that we all used IntelliJ for are is slowly being integrated into the other IDEs. I think IJ is still the best, but their margin is slowing being reduced. If the folks over at JetBrains want to stay competitive they are gonna need more speed, more productivity, more simplicity and more power. These things are all hard to get at the same time, but I’m confident that they will find at way.

For now, I’m gonna give NetBeans the full shake-down, log a ton of bugs and wait for 7.0 to see how many they fix. I’d say my list is pretty short at this point and I could envision a full switch to NetBeans with 5-10 enhancements if IntelliJ continues its slow decline.

Only time will tell.