Looping through a Char array - splitting into seperate Strings - Arduino

Question

I am having a bit of difficulty with the Arduino project I am currently working on.

The purpose of the function I am developing is to take in a char array variable received via an NRF wireless module and separate this into 2 different string variables. The first 13 characters into one string, and the remaining into another.

void receiveData(char* receivedData){ // Function to place the received data into the correct variable.
  for(int i = 0;i < sizeof(receivedData);i++){
    if(i < 13){
      String variableName = variableName + receivedData[i]; // Builds a string of the variablename.
    }
    else{
      String value = value + receivedData[i]; // Builds a string of the value.
    }   
  }

I have worked through a few different ways but no luck.

Any help will be greatly appreciated, Thank you!

Does this answer your question? C++: sizeof for array length — Timo
– Timo, Commented Mar 18, 2020 at 14:24
variableName stays in the scope of your if loop, so once you enter your for loop again, all changes made to variableName will dissapear. You should declare value and variableName outside your for loop (String variablename, value;) — Arno Deceuninck
– Arno Deceuninck, Commented Mar 18, 2020 at 14:24
sizeof(receivedData) is the same as sizeof(char*), which will be 4 or 8 depending on the platform (probably 4 on an Arduino). You need to pass the size to the function. — molbdnilo
– molbdnilo, Commented Mar 18, 2020 at 14:24

pablo285 · Accepted Answer · 2020-03-18 14:26:49Z

3

String variableName = variableName + receivedData[i];

Here you are defining the variable in every iteration of the loop. You should declare the variable before the loop:

String variableName;
for () {
    variableName = whatever;
}

In addition sizeof(receivedData) will only give you size of the pointer, not the size of the string that you probably expect.

answered Mar 18, 2020 at 14:26

pablo285

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3 Comments

Paul James Over a year ago

I see that, thankyou. The problem I am getting is say I pass the char array of "voltageBefore34", when I serial print and monitor this output of variableName, I only get 'vvo' and I am unsure why.

pablo285 Over a year ago

Can't really answer that, I strongly suggest that you use a debugger and do a step-by-step analysis of what your loop is doing.

Paul James Over a year ago

I have got it working, Pablo. Thank you very much for your help. much appreciated!

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