C++: How do I pass N arguments to a function where N can be any number > 0? (The function already exists as part of an external library)

Question

This is the way I currently call the function:

struct fann *ann = fann_create_standard(
                          num_layers, 
                          num_in,
                          optional_num_1, 
                          optional_num_2, 
                          num_out);

the function above can have at least 3 arguments... the required arguments are num_layers, num_input, and num_output)

the optional arguments are the hidden layers of the neural network (what they are call isn't important.... but basically... it could look like this:

fann_create_standard(#layers, 
                       #input,
                       #hidden1,
                       #hidden2,
                       #hidden3,
                       #hidden4,
                       ...,
                       #hiddenN,
                       #output);

what I want to be able to do, is pass in command line arguments to change how many layers, and what the values of each of the hidden layers are (the middle arguments in this function call), so that I don't have to re-compile the program every time I want to re-configure the network.

Hello again. http://stackoverflow.com/questions/5570131/c-how-do-i-pass-a-variable-for-multiple-arguments/5570189#5570189 — Chris Eberle, Apr 06 '11 at 17:27

score 2 · Accepted Answer · answered Apr 06 '11 at 17:33

2

can't you use fann_create_standard_array to do what you want? Arrays can be dynamically created, whereas argument lists should be specified during compilation.

answered Apr 06 '11 at 17:33

Assambar

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score 2 · Answer 2 · answered Apr 06 '11 at 17:41

Add the stdarg.h library file into your program.

In your case your function definition will be:

fann_create_standard(num_layers , num_in , num_out , int count,  ... );

Then you can access your optional parameters using the va_start, va_args, va_end macros and the va_list type to retrieve your optional parameters. The new "count" parameter holds the amount of parameters you pass to the method, so:

fann_create_standard(num_layers , num_in , num_out , int count,  ... ){
  int i;
  YOUR_TYPE val;
  va_list vl;
  va_start(vl,count);
  for (i=0;i<count;i++)
  {
    val = va_arg(vl,YOUR_TYPE);
    //val is your optional parameter, do whatever you'd like with it
  }
  va_end(vl);
}

score 0 · Answer 3 · answered Apr 06 '11 at 17:27

0

What you're looking for is a variadic function

answered Apr 06 '11 at 17:27

yan

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No, he already has a variadic function, but he wants to know how to change the number of passed parameters to the function *at runtime*. – Mark B Apr 06 '11 at 17:30

C++: How do I pass N arguments to a function where N can be any number > 0? (The function already exists as part of an external library)

3 Answers3