2

i'm still new to arduino and also to C++ and have a short question. What i want to do is to write a function (in my case to parse the query-string of an URL) to get the parameter names and values (varying number of parameters).

My function looks like the following:

String function readParams()
{
   String params[x]; // x: number of params

   // fill params[0]... params[x] with parameter names

   return params;
}


void loop()
{
   // do some stuff

   String params[x] = readParams();

   for(int i=0; i < x; i++)
   {
      debug(params[i]);
   }
}

What is the correct return-type for the readParams() function in this case? And how to access the params in the main (loop) -function?

I hope the code makes it clear what i want to do.

Thanks, Marius

2

Some tips:

  1. Don't use String.
  2. Use char * and slice the string in-place.
  3. Pass a pointer to an array of pointers and fill that with pointers to the portions of the string you have sliced.
  4. Return the number of entries in the array you used.

I do something similar in my CLI library. I use a custom "getWord" function, but similar can be done with strtok().

You can read more about working with C strings here.

| improve this answer | |
1

I'm inclined to agree with Majenko that you shouldn't use String in the first place, but if you want to, you can pass by reference:

const int numParams = 2;

void readParams(String (& params) [numParams])
  {
  params [0] = "foo";
  params [1] = "bar";
  }

void setup() 
{
  Serial.begin (115200);
  String params [numParams];
  readParams (params);
  for (int i = 0; i < numParams; i++)
    Serial.println (params [i]);
}

void loop() { }

An easier thing is to make the parameters a global variable.

| improve this answer | |
  • what if number of parameters is not known in the beginning ? how would you initialize numPaams then ? – Ciasto piekarz May 25 at 12:18
  • Typically you would use new and make an array of whatever it is you want to make multiple copies of. Or you could consider the STL (Standard Template Library) which supports things like vectors. – Nick Gammon May 26 at 6:44

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.