Fun C++ code

As a programmer I will sometimes do some code because I feel it works out the best with minimal effort, also trying to adhere to the KISS principal (Keep it Simple Stupid).

One of the things I have been abusing as of late is the STL Map object. I have the following need: I have to take in user input from a socket (I use a socket object I wrote here, that works just like cin and cout) and I need to run one of many functions. All the functions have the same function signature. so lets assume that a function looks like this
void function(void *);
First I know void pointers, but I am only doing an example so don’t freak out. Now back to it. Now lets say you have 20 to 40 functions like this. And you will pick one based on the input that comes in from the user via a socket connection. the incoming info is plain text, it could be read in from a command line for all I care. A fast way to pick the right function (IMO) is to use a STL Map object. So I would declare the object in the following way
std::map FunctionPicker;
filling the map object is easy
FunctionPicker[“function1”] = &function;
FunctionPicker[“function2”] = &printingFunction;
Running a function after getting is easy, also remember if the index into map does not exist it return 0 or in the case of a function pointer we can check for NULL. So you want a variable declared in the following way.
void (*funPtr)(void *); // Yes I know funPtr is not all that creative
// of a name but it gives an idea what it does
So to get the function pointer from the map and run the function you would want to do the following.
funPtr = FunctionPicker[userinput]; // lets assume that userinput is declard as
// std::string
if(funPtr == NULL)
// put some error handling code here
(*funPtr)(); // since funPtr is now a pointer to the
// function we want to run, we need to
// deference it and then call it
Now is that not easy and we let the coders that wrote the STL do the hard work for us, and we don’t have an ugly if, else if, else tree in the code. Plus adding a new function is as easy as writing the code for the new function, and adding the entry to the Map object.
I would love to see what others have done to deal with this situation. Or what is your favorite programming tool you use or abuse.

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Categories: Geekdom Programming Technology
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Published on: January 11, 2006

 Comments (1) 

  1. Max says:

    Sadly, I do fluff stuff now – web programming. It pays very well, but the last time I wrote object-oriented code was in college (I’m not exactly missing it). My favorite thing to do was overloading a function and in Perl, you don’t need to do anything special. All the parameters to the Perl function are stored in an array (similar to other langues). However, Perl functions don’t care about how many parameters there are, so your function could be like:

    sub myFunc
    my($param1, $param2) = @_;

    where @_ is the array that holds the parameters (no matter how many there are). The $param1/$param2 variables are set based on the order of variables I pass into the function, all dynamic, so I can have zero or infinite parameters, Perl handles it all. So I can pass values and flags instead of using global configuration variables or multiple functions with similar code.

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