Operator[] error

This is a discussion on Operator[] error within the C++ Programming forums, part of the General Programming Boards category; I've just ran into a problem with this: Code: #include "stdafx.h" using namespace std; class HashTable { int data[100]; public: ...

  1. #1
    Supermassive black hole cboard_member's Avatar
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    Operator[] error

    I've just ran into a problem with this:

    Code:
    #include "stdafx.h"
    
    using namespace std;
    
    class HashTable
    {
        int data[100];
    
    public:
        HashTable();
        ~HashTable();
    
        int operator[](char *rhs);
    };
    
    HashTable::HashTable()
    {
        for (int i = 0; i < 100; i++)
            data[i] = 0;
    }
    
    HashTable::~HashTable()
    {
    
    }
    
    // operator[]
    int HashTable::operator[](char *rhs)
    {
        int hash = 0;
        int i = 0;
    
        // construct a hash from the string
        for (; *(rhs + i) != 0; i++)
            hash += static_cast<int>(*(rhs + i));
    
        cout << "hash: " << hash << endl;
        return 0;
    }
    
    
    int main(int argc, char* argv[])
    {
        HashTable *ht = new HashTable();
    
        ht["lee"];
    
        delete ht;
        return 0;
    }
    Error:

    Code:
    c:\Documents and Settings\lee\Desktop\sandbox\sandbox.cpp(46) : error C2107: illegal index, indirection not allowed
    Tis the first time I've had this error. I'm scared.
    Oh I know the hash algorithm is corny and the data array seems a bit pointless, but I have plans, glorious glorious plans!.
    Good class architecture is not like a Swiss Army Knife; it should be more like a well balanced throwing knife.

    - Mike McShaffry

  2. #2
    C++ Witch laserlight's Avatar
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    hmm... perhaps you mean to write:
    Code:
    (*ht)["lee"];
    instead?

    Oh, and remember that subscript operators often come in pairs.
    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

  3. #3
    Supermassive black hole cboard_member's Avatar
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    Quote Originally Posted by laserlight
    hmm... perhaps you mean to write:
    Code:
    (*ht)["lee"];
    instead?

    Oh, and remember that subscript operators often come in pairs.
    I can't get my head around why the indirection is necessary.
    Good class architecture is not like a Swiss Army Knife; it should be more like a well balanced throwing knife.

    - Mike McShaffry

  4. #4
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    Because ht is a pointer. So to call a member function of the class like operator[], you need to dereference the pointer.

  5. #5
    Supermassive black hole cboard_member's Avatar
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    Oh yeah I see. Sorry I wasn't recalling operator[] is a function.

    Oh yeah you can do this:

    Code:
    ht->operator[]("lee");
    Neat. Well that's the thing I learnt today \/
    Good class architecture is not like a Swiss Army Knife; it should be more like a well balanced throwing knife.

    - Mike McShaffry

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