2D Vector won't compile

[chisser98]

Hello everyone,

I'm having some difficulty with initializing my Vector. I'm trying to simulate a 2d array with vectors. The source looks good to me, but for some reason I'm getting an error at compile time.

In my Main.h file, I have the line:
std::vector< std::vector<char> > terrain;
which compiles ok.

In my Main.cpp file, I have the line:
this->terrain( Main::MAP_HEIGHT, std::vector<char>(Main::MAP_WIDTH, 'T') );
which ends up throwing this error:

../Main.cpp:93: error: no match for call to ‘(std::vector<std::vector<char, std::allocator<char> >, std::allocator<std::vector<char, std::allocator<char> > > >) (const int&, std::vector<char, std::allocator<char> >)’

MAP_HEIGHT and MAP_WIDTH are defined in my .h file as 10 and 20, respectively.

Does anyone have any idea why this error is occuring?

Thanks for any suggestions!

Chisser98

[jsmith]

You are ... sort of ... attempting to call the vector<> constructor with your line of code
since you haven't actually specified the function to call.

First, I assume that the line of code is inside some class instance since you are using
this->.

What you want is vector<>::assign:

terrain.assign( Main::MAP_HEIGHT, std::vector<char>( Main::MAP_WIDTH, 'T' ) );

[chisser98]

Hi jsmith,

Thank you for your reply, the vector<>::assign method compiled perfectly!

And yes, I was attempting to call the vector<> constructor. I saw an example that did this:

vector< vector<int> > vI2Matrix(3, vector<int>(2,0));

to create a '2d array' with vectors. So I split mine up and put the declaration of the variable in Main.h and the initialization in Main.cpp. Out of curiosity, any idea why what I was doing didn't work?

Thanks again for the reply!

Cheers

[jsmith]

Variables can only be constructed at the point of instantiation.
This instantiates a variable named v and runs its constructor:

std::vector<char> v( 5, 'X' );  // v is now { 'X', 'X', 'X', 'X', 'X' } 

In your code, "terrain" was already instantiated elsewhere. Consequently,
the compiler was thinking that you wanted to call std::vector<...>::operator()
with the parameters Main::MAP_HEIGHT and std::vector<char>(Main::MAP_WIDTH, 'T').
But std::vector<> does not provide the function call operator.

I'm not sure where exactly you put that line of code -- be it in a class constructor or
elsewhere. For example, it is a common beginner (not saying you are one--I don't
know) error to do something like this:

class MyClass {
   std::vector<char> v;
  public:
   MyClass();
};

MyClass::MyClass()
{
   v( 5, 'X' );  // Wrong
}

The right way would be to put that line of code in an initializer list:

MyClass::MyClass() :
   v( 5, 'X' )  // Right!
{
}

Or, a bad, but workable solution would be:

MyClass::MyClass()
{
   v = std::vector<char>( 5, 'X' );  // OK, but the previous solution is preferred
}

[chisser98]

Ahh okay, that makes perfect sense then. Thanks jsmith!

I'm experienced in Java and just learning the ropes of c++. Thanks again for the help!