Using operator "()" inside boost matrix

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  1. #1
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    Using operator "()" inside boost matrix

    Hi,

    I've wrote a class inherit from boost matrix, however, I can't figure out how to access the random access operator "()" inside the class.

    For instance, I can use "()" outside the class by m.(x, y) = some_value, however, inside the class I can't just using (x, y) = some_value, although my compiler didn't complain this way, some_value will not be assigned successfully.

    Neither this(x, y), *this(x, y), this->(x, y) will pass the compiler. (I have to confess that I'm not familiar with the usage of "this"...)

    Besides, I can't examine the value of x_location and y_location inside the following for-loop, is it a bug of gdb?

    Here is my code, any idea?

    Code:
    #ifndef TARGET_REGION_H
    #define TARGET_REGION_H
    
    #include <iostream>
    #include <vector>
    #include <utility>
    #include <boost/numeric/ublas/matrix.hpp>
    #include <boost/numeric/ublas/io.hpp>
    
    using namespace std ;
    using namespace boost::numeric ;
    
    class Target_Region: public ublas::matrix<bool>
    {
    public:
    	Target_Region( const int width, const int height, const vector<int> to_be_inpaint_vec_x, const vector<int> to_be_inpaint_vec_y )
    	{
    		assert( to_be_inpaint_vec_x.size() == to_be_inpaint_vec_y.size() ) ;
    
    		bool preserve_previous_value = false ;
    		resize( width, height, preserve_previous_value ) ;
    
    		// for each pixel location in to_be_inpaint_vec, markup to true in the target region
    		vector<int>::const_iterator x_location_iter = to_be_inpaint_vec_x.begin() ;
    		vector<int>::const_iterator y_location_iter = to_be_inpaint_vec_y.begin() ;
    		int x_location = 0 ;
    		int y_location = 0 ;
    		for( ; x_location_iter != to_be_inpaint_vec_x.end() ; ++x_location_iter, ++y_location_iter )
    		{
    			x_location = *x_location_iter ;
    			y_location = *y_location_iter ;
    			( x_location, y_location ) = true ;
    		}
    	}
    
    private:
    
    };
    
    
    #endif
    Last edited by jutirain; 02-17-2008 at 09:21 PM.

  2. #2
    C++ Witch laserlight's Avatar
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    For instance, I can use "()" outside the class by m.(x, y) = some_value, however, inside the class I can't just using (x, y) = some_value, although my compiler didn't complain this way, some_value will not be assigned successfully.
    That's because:
    Code:
    ( x_location, y_location ) = true ;
    becomes:
    Code:
    y_location = true ;
    Neither this(x, y), *this(x, y), this->(x, y) will pass the compiler. (I have to confess that I'm not familiar with the usage of "this"...)
    You should use (*this)(x, y) or more explicitly, operator()(x, y).

    By the way, are you sure Boost's matrix classes are designed to be base classes? I would expect them to follow the C++ Standard Library convention, and the standard containers are not designed to be base classes.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    Hi laserlight,

    You're right. Using operator()(x, y), my program now executes as expected.
    Thanks a lot.

    However, I'm not very sure about why STL containers should not be base classes.

  4. #4
    C++ Witch laserlight's Avatar
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    However, I'm not very sure about why STL containers should not be base classes.
    Read:
    When should my destructor be virtual?
    Why are destructors not virtual by default?
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  5. #5
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    Thanks for your information.

    So, if my self-defined container hold an "is-a" relationship (I know I can do it by "has-a" relationship, however, that's awkward) with some STL container, and I want the convenience from inheritance and some self-defined functionality, what may be the better approach?

  6. #6
    C++ Witch laserlight's Avatar
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    So, if my self-defined container hold an "is-a" relationship (I know I can do it by "has-a" relationship, however, that's awkward) with some STL container, and I want the convenience from inheritance and some self-defined functionality, what may be the better approach?
    You can either do the right thing and just use composition ("has-a"), fowarding functions if necessary, or you can ignore the fact that you are deriving from a class that is not designed to be a base class and risk undefined behaviour if someone attempts to use polymorphism through a base class pointer that has delete or delete[] applied to it.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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