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POTemplated 2D Array Error
 

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    <p>Dear Sir, When I read an on-line book titled "Data Structures and Algorithms with Object-Oriented Design Patterns in C++", I cut and paste some code snippets from the section "Two-Dimensional Array Implementation" (please see this link for your reference <a href="http://www.brpreiss.com/books/opus4/html/page102.html" rel="nofollow">http://www.brpreiss.com/books/opus4/html/page102.html</a>) as follows:</p> <pre><code>#include "Array1D.h" template &lt;class T&gt; class CArray2D { protected: unsigned int m_nRows; unsigned int m_nCols; CArray1D&lt;T&gt; m_Array1D; public: class Row { CArray2D&amp; m_Array2D; unsigned int const m_nRow; public: Row(CArray2D&amp; Array2D, unsigned int nRow) : m_Array2D(Array2D), m_nRow(nRow) {} T&amp; operator [] (unsigned int nCol) const { return m_Array2D.Select(m_nRow, nCol); } }; CArray2D(unsigned int, unsigned int); T&amp; Select(unsigned int, unsigned int); Row operator [] (unsigned int); }; </code></pre> <hr> <pre><code>#include "StdAfx.h" #include "Array2D.h" template &lt;class T&gt; CArray2D&lt;T&gt;::CArray2D(unsigned int nRows, unsigned int nCols) :m_nRows(nRows), m_nCols(nCols), m_Array1D(nRows * nCols) { // The constructor takes two arguments, nRows and nCols, which are the desired dimensions of the array. // It calls the CArray1D&lt;T&gt; class constructor to build a one-dimensional array of size nRows * nCols. } template &lt;class T&gt; T&amp; CArray2D&lt;T&gt;::Select(unsigned int nRows, unsigned int nCols) { if (nRows &gt;= m_nRows) throw std::out_of_range("invalid row"); if (nCols &gt;= m_nCols) throw std::out_of_range("invalid column"); return m_Array1D[nRows * m_nCols + nCols]; } template &lt;class T&gt; CArray2D&lt;T&gt;::Row CArray2D&lt;T&gt;::operator [] (unsigned int nRow) { return Row(*this, nRow); } </code></pre> <p>When I compile (Microsoft VS 2008 C++ compiler) the above code, I got the following errors:</p> <pre><code>&gt;Compiling... 1&gt;Array2D.cpp 1&gt;f:\tips\tips\array2d.cpp(27) : warning C4346: 'CArray2D&lt;T&gt;::Row' : dependent name is not a type 1&gt; prefix with 'typename' to indicate a type 1&gt;f:\tips\tips\array2d.cpp(27) : error C2143: syntax error : missing ';' before 'CArray2D&lt;T&gt;::[]' 1&gt;f:\tips\tips\array2d.cpp(27) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int 1&gt;f:\tips\tips\array2d.cpp(27) : fatal error C1903: unable to recover from previous error(s); stopping compilation 1&gt;Build log was saved at "file://f:\Tips\Tips\Debug\BuildLog.htm" 1&gt;Tips - 3 error(s), 1 warning(s) ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ========== </code></pre> <p>Could you take some time to figure out my problems? </p> <p>Thank you in advance.</p> <p>Golden Lee</p>
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    1. COsearch google for "Dependent types" C++, basically `CArray2D<T>::Row` cannot be resolved to a type by the compiler, you have to explicitly tell the compiler it's a type by using the `typename` key word. Search this site, there are LOTS of questions and answers on this topic...
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