Yeah, but in first.cpp it declares 'external int' without the 'extern' keyword. But, because of its name, I pressume it also is external.

So does the 'extern int externalInt' declaration in second.ccp create a new variable or does it refer to the same thing as the external int in first.cpp?

Todays subject: internal and external linkage!

I'm just reading about namespaces in my C++ book for the first time. It began by introducing the subject of linkage, but its description is rather unclear.

here's my books description:

Linkage
Names can have internal and external linkage. These two terms refer to the use or availability of a name across multiple translation units or within a single translation unit. Any name having internal linkage can only be referred to within the translation unit in which it is defined. Names having external linkage are available to other translation units.

okay, but they don't explain what a 'translation unit' is. Immediatley after it uses the following listings to demonstrate internal and external linkage

first.cpp

int externalInt = 5;
const int j = 10;
int main()
{
  return 0;
}

second.cpp

extern int externalInt;
int anExternalInt = 10;
const int j = 10;

after this it says the externalInt variable defined in line 1 of first.cpp has external linkage.

I don't follow. First, this is the first time i have ever seen the 'extern' keyword. So i'm not sure what the first line in second.cpp means, and how many instances of externalInt there are.

Usually my book explains things better than this.  Can anyone explain to me whats happening between these two .cpp files?

& is proper, because you want that function's address.

pointers to functions anyway as it seems to be a discouraged technique

Not really, however it is fairly rare when they are used.  See std::sort for a proper example.

the license is apparently about 17 years old...

Yes, however this does not mean that the compiler is.  A license appears from the start date.  So if I start a website in 2000 and keep it running till 2008, I would still put a copyright of 2000 on it.

Bloodshed Dev-C++ is a full-featured Integrated Development Environment (IDE) for the C/C++ programming language. It uses Mingw port of GCC (GNU Compiler Collection) as it's compiler. Dev-C++ can also be used in combination with Cygwin or any other GCC based compiler.

If you don't know what this means here is a bit of an explanation.  The compiler is a program which takes input files (and some addition parameters) and spits out some type of byte-code.  Compilers, like any programs, must be run in some form.  As with any program, it must be run.  Since the compiler typically requires input (namely, code) it must be run from the command line.

That's all fine and dandy, but compilers being run from the command line can be typically hard to use.  It is tedious to type in a line every time you want to compile.  Also, there are many options which can make that line very long and confusing.  In order to simplify this, a Integrated Developement Environment is used.  All an IDE is, is a program which runs a compiler.  As such, they are almost always not connected, but rather the IDE just generates that compile line for you.  It would be rather idiotic for an IDE to not come with a text editor to allow you to modify your code, and some even have debugging tools.

So in the above quote, Bloodshed is just an IDE.  It runs off the Mingw port of GCC.  GCC, in turn, is the standard compiler used by Linux systems.  I'd have to do some testing with Mingw, but it looks like if that was your code, then there is a pretty darn big bug in the compiler.

What compilers are you using?  Need name and version numbers.

It's just a typo I believe.

#include <iostream>

class Dog
{
  public:
  Dog() {}
  ~Dog() {}
  
  // method to be pointed to
  int bark(long l, double d) { std::cout << "bark " << (l*d) << " times\n"; return 0; } 
};

int main()
{
  // declare pointer to any dog method that takes a long and a double and returns an int
  int (Dog::*p)(long, double); 
  p = &Dog::bark; // bad???
  Dog pokey;
  (pokey.*p)(2,4);
  return 0;
}

It is an array of 1 dimensional arrays, but in order to be able to create a data structures such as that, you need to define the structure.  With an array, you tell the computer "give me an array of size 10".  With a (dynamic) matrix, you can't just say "give me a matrix of size 5x4".  This is because the memory itself is shaped like an array, but it's not shaped like a matrix.  This makes creating arrays more natural than doing so with a matrix.

i agree a matrix is like an array of arrays, but C++ does not seem to agree in terms of syntax.

?

A matrix is an array of arrays, but this view is naive because you can't just say to your computer, "Make me an array of arrays".  You need to define more structure behind it.  OO programming allows you to do this very naturally:

vector<vector<int> > matrix;