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POWhy can't I make objects in C++ have data-members that are other objects?
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copied!<p>I was bored one day, so I made this library:</p> <pre><code>template <class X, class Y> class HASH { public: HASH(X element, Y key) { elements=new X[0]; keys=new Y[0]; keys[0]=key; elements[0]=element; num_elements=0; }; ~HASH () { delete[] elements; delete[] keys; }; void Add(X element, Y key) { for (int x=0; x<=num_elements; x++) { if (keys[x]==key) { throw(key); } } //make copy variables X *copy_elements=new X[num_elements]; Y *copy_keys=new Y[num_elements]; //copy all the elements for (int x=0; x<=num_elements; x++) { copy_elements[x]=elements[x]; copy_keys[x]=keys[x]; } //delete the originals delete[] elements; delete[] keys; //resize the originals elements=new X[num_elements+1]; keys=new Y[num_elements+1]; //copy everything back to the originals for (int x=0; x<=num_elements; x++) { elements[x]=copy_elements[x]; keys[x]=copy_keys[x]; } //delete the copies delete[] copy_keys; delete[] copy_elements; //increment num_elements num_elements++; //add the new elements elements[num_elements]=element; keys[num_elements]=key; }; X operator [] (Y key) { int num=0; for (int x=0; x<=num_elements; x++) { if (keys[x]==key) { num=x; break; } } return elements[num]; }; Y KeyNum(int x) { return keys[x]; }; int NumElements() { return num_elements; }; private: int num_elements; X *elements; Y *keys; }; </code></pre> <p>and then I tested it, and it worked. So now I am trying to create an experiment whose source code is this:</p> <pre><code>#include <hash.cpp> #include <iostream> using namespace std; class OBJECT { public: OBJECT(string name, int number) { int_properties=new HASH <string, int>; }; ~OBJECT() { delete int_properties; }; HASH <string, int> *int_properties; }; int main() { OBJECT a("name", 5); return 0; } </code></pre> <p>and it is returning the error:</p> <pre> brain.cpp: In constructor ‘OBJECT::OBJECT(std::string, int)’: brain.cpp:10: error: no matching function for call to ‘HASH<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int>::HASH()’ /usr/include/hash.cpp:4: note: candidates are: HASH<X, Y>::HASH(X, Y) [with X = std::basic_string<char, std::char_traits<char>, std::allocator<char> >, Y = int] /usr/include/hash.cpp:2: note: HASH<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int>::HASH(const HASH<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int>&) </pre> <p>I have made a whole lot of tests, and no matter what I do, I can't seem to initialize an object that is the data-member of another object. I just don't understand why.</p>

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