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Industrial Strength Hash Table

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17 replies to this topic

#1 Phil123   Members   -  Reputation: 719

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Posted 12 March 2014 - 12:26 PM

I've been enjoying the coding horrors forum for a while, so I decided to post a snippet of code that I found in a large c++ project that I'm (unfortunately) a part of.  Normally I wouldn't poke fun at code like this, but I couldn't resist this one.

 

Enjoy.

#pragma once

#include "Includes.h"



template<class T>

class Dictionary

{

private:

    std::vector<std::string> keys;

    std::vector<T> values;

public:

    Dictionary()

    {

        keys = new std::vector<std::string>{};

        values = new std::vector<T>{};

    }



    ~Dictionary()

    {

        delete[] keys;

        delete[] values;

    };



    std::vector* Values() { return &values; };

    std::vector* Keys() { return &keys; };



    size_t size() { return keys.size(); }



    void Add(std::string _key, T value)

    {

        keys.push_back(_key);

        values.push_back(value);

    };

    void Remove(std::string _key)

    {

        for (size_t i = 0; i < keys.size(); i++)

        {

            if (keys.at(i) == _key)

            {

                keys.erase(keys.begin() + i);

                values.erase(values.begin() + i);

                break;

            }

        }

    };

    T Get(std::string _key)

    {

        for (size_t i = 0; i < keys.size(); i++)

        {

            if (keys.at(i) == _key)

            {

                return values.at(i);

            }

        }

        return nullptr;

    };

};



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#2 TheComet   Crossbones+   -  Reputation: 1640

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Posted 12 March 2014 - 01:08 PM

So let's see what the WTFs basically are...

  • Assigning a pointer generated from new to a type that is not a pointer
  • Using delete[] on objects created with new and not new[]
  • Using braces instead of brackets for trying to call the constructor of an object
  • Returning a pointer pointing to what is supposed to be an array of pointers pointing to pointers (given the new[] and delete[]), even though the value being returned isn't of type pointer (which is a double-WTF because if it were to compile, that would still be retarded)
  • using a lookup method of complexity O(n)
  • Attempting to declare a return type without template arguments.
  • Returning a nullptr in the case of not finding an entry, implying that the templated type is always a pointer.
  • Method names begin with a capital letter
  • not using std::map
  • code doesn't even compile

Evaluation:

 

tumblr_mc2w7cEoiz1qmiwbe.png


Edited by TheComet, 13 March 2014 - 05:52 AM.

YOUR_OPINION >/dev/null

#3 Rattrap   Members   -  Reputation: 1785

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Posted 12 March 2014 - 01:19 PM

#include "Includes.h"

 

Got to love the all encompassing include.


Method names begin with a capital letter

This one is excusable, since that is just personal preference.  I personally don't like camelCase.



#4 ferrous   Members   -  Reputation: 2145

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Posted 12 March 2014 - 01:40 PM

Yeah, my favorite is that the person is using std::Vector, but didn't bother to look for existing hash table functionality.  Or maybe they did but their google fu sucks.  

 

And I agree with Rattrap, the capital letter on method names is actually the coding guideline here at my work.  



#5 Krohm   Crossbones+   -  Reputation: 3245

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Posted 13 March 2014 - 02:07 AM

One also wonders why they didn't made a pair to use a single vector.

Want to talk about exception safety?



#6 Hodgman   Moderators   -  Reputation: 31785

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Posted 13 March 2014 - 02:30 AM

Does that code even compile? In what compiler?



#7 Mona2000   Members   -  Reputation: 623

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Posted 13 March 2014 - 05:09 AM

Does that code even compile? In what compiler?

 

In every compiler.

 

 

 

 

As long as you don't use that template.



#8 Juliean   GDNet+   -  Reputation: 2720

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Posted 13 March 2014 - 05:42 AM


So let's see what the WTFs basically are...

 

I would add:

 

- Creating the std::vectors with new, where they would better be created on the stack. Its not like one of the vectors benefits is that it takes away the memory management for dynamic arrays.

 

- Returning both vectors as non-const pointer, basically breaking every concept of encapsulation of that class. Especially hard since both vectors are meant to store dependant values for one entry, imagine someone deleting values out of only the Value-vector.

 

- Also, returning the vectors by pointer instead of reference when they can never be nullptr.



#9 ByteTroll   Crossbones+   -  Reputation: 1500

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Posted 13 March 2014 - 05:49 AM


Method names begin with a capital letter

 

Hey! What's wrong with this? rolleyes.gif

 

I would like to add one.  How about every line being spaced with the beginning of each function being double spaced.  That might be "personal" preference, but it is a hell of an annoying one.

 

 

Does that code even compile? In what compiler?

 

In every compiler.

 

 

 

 

As long as you don't use that template.

 

 

Hehehehe.

EDIT: Or the fact that every function is terminated with a semicolon.  Again, personal preference; hell of an annoying one.


Edited by ByteTroll, 13 March 2014 - 05:52 AM.

▬▬▬▬▬▬▬▬▬▬▬ஜ۩۞۩ஜ▬▬▬▬▬▬▬▬▬▬▬▬▬
I see the future in 1's and 0's
▬▬▬▬▬▬▬▬▬▬▬ஜ۩۞۩ஜ▬▬▬▬▬▬▬▬▬▬▬▬▬

"This is called programming. The art of typing shit into an editor/IDE is not programming, it's basically data entry. The part that makes a programmer a programmer is their problem solving skills." - Serapth

#10 TheComet   Crossbones+   -  Reputation: 1640

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Posted 13 March 2014 - 05:49 AM

 

Does that code even compile? In what compiler?

 

In every compiler.

 

As long as you don't use that template.

 

Not instantiating a template doesn't prevent the first compilation pass, which will catch syntactical errors such as:

std::vector* Values() { return &values; }; // invalid use of template-name "std::vector" without an argument list

Edited by TheComet, 13 March 2014 - 05:50 AM.

YOUR_OPINION >/dev/null

#11 l0calh05t   Members   -  Reputation: 816

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Posted 13 March 2014 - 06:11 AM


Using braces instead of brackets for trying to call the constructor of an object

 

That's actually valid in C++11 and called uniform initialization syntax.



#12 TheComet   Crossbones+   -  Reputation: 1640

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Posted 13 March 2014 - 06:23 AM

 


Using braces instead of brackets for trying to call the constructor of an object

 

That's actually valid in C++11 and called uniform initialization syntax.

 

Thanks for the clarification. I learned something new today!


YOUR_OPINION >/dev/null

#13 HyperV   Members   -  Reputation: 870

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Posted 14 March 2014 - 03:53 AM

i'm starting to have a trauma



#14 TheComet   Crossbones+   -  Reputation: 1640

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Posted 14 March 2014 - 05:46 AM


EDIT: Or the fact that every function is terminated with a semicolon.  Again, personal preference; hell of an annoying one.

WTF I didn't notice that at first.


YOUR_OPINION >/dev/null

#15 samoth   Crossbones+   -  Reputation: 5032

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Posted 14 March 2014 - 05:48 AM

Using delete[] on objects created with new and not new[]

Relax, it is much worse than you think.laugh.png

 

delete[] is being called on objects which are not explicitly allocated via new at all. The vectors that are allocated on the heap are copied (if the compiler accepts this code at all!) and then leaked. I wonder how you can assign a pointer-to-vector to a vector though, since to my knowledge it only accepts const T& and T&& and std::initializer_list<T>.

 

Both keys and values are objects, not pointers, and part of the Dictionary object. Which means that you call delete (with or without brackets, who cares) on an object that is either allocated on the stack or inside a larger heap-allocated object. In either case, this is very bad mojo.

 

The Dictionary class has no virtual functions and keys is the first member, so likely (void*) keys == (void*) dictionary_object

Which means if you somehow get the compiler to accept this code (I would be surprised, though), it would double-delete the Dictionary object, once explicitly and once from its own destructor via a type-punned std::vector pointer.


Edited by samoth, 14 March 2014 - 05:49 AM.


#16 Phil123   Members   -  Reputation: 719

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Posted 14 March 2014 - 12:48 PM


EDIT: Or the fact that every function is terminated with a semicolon. Again, personal preference; hell of an annoying one.

 

Haha, but get this, only some functions are terminated with a semicolon.  Others aren't.



#17 Oberon_Command   Crossbones+   -  Reputation: 1960

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Posted 16 March 2014 - 03:36 PM

This looks like Java code that someone tried to port without an actual understanding of C++.



#18 swiftcoder   Senior Moderators   -  Reputation: 10361

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Posted 16 March 2014 - 03:49 PM

This looks like Java code that someone tried to port without an actual understanding of C++.

That reminds me of a joke which has become decidedly unfunny on my current project:

 

What's worse than C++ written by a Java developer?

 

Spoiler


Tristam MacDonald - Software Engineer @Amazon - [swiftcoding]






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