function returning String-Array

Question 1

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

Question 2

Some tips:

Don't useString.
Usechar * and slice the string in-place.
Pass a pointer to an array of pointers and fill that with pointers to the portions of the string you have sliced.
Return the number of entries in the array you used.

I do something similar in myCLI library. I use a custom "getWord" function, but similar can be done withstrtok().

You can read more about working with C stringshere.

Question 3

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.

Question 4

what if number of parameters is not known in the beginning ? how would you initializenumPaams then ?

Question 5

Typically you would usenew 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.

Majenko 106k5 gold badges82 silver badges139 bronze badges · Answer 1 · 2018-03-13 14:09:07Z

Some tips:

Don't useString.
Usechar * and slice the string in-place.
Pass a pointer to an array of pointers and fill that with pointers to the portions of the string you have sliced.
Return the number of entries in the array you used.

I do something similar in myCLI library. I use a custom "getWord" function, but similar can be done withstrtok().

You can read more about working with C stringshere.

Nick Gammon♦ 38.9k13 gold badges70 silver badges126 bronze badges · Answer 2 · 2018-03-13 21:59:55Z

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.

what if number of parameters is not known in the beginning ? how would you initializenumPaams then ?
Typically you would usenew 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.

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