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Arduino wire can't send char

Hi I have problem with school project. I have 3 Arduino - 1 Transmiter with NRF; 2,3 - NRF receiver and wire slave receiver. I can't send data via "Wire" library (in code char "datar") to receiver arduino. I won't get anything, but when I want to send like Wire.write("blablabla"); it pass. But when in char is NRF data code crashing when go to "Wire.write".

/*
*/
#include <Wire.h>
#include <SPI.h>
#include "RF24.h"

char datar = '';

//Konfiguracja
const uint64_t pipes[2] = {0xF1F2F3F0F7/*odbieranie*/, 0xF1F2F3F0F8/*wysylanie*/};
RF24 radio(9, 10); //Piny nrf (SPI) 9 i 10
//-- Konfiguracja

void setup() {
  Serial.begin(9600);
  Serial.println("LOL");
  Wire.begin();
  radio.begin();
  radio.setPALevel(RF24_PA_MAX);
  radio.setDataRate(RF24_250KBPS);
  radio.openReadingPipe(1, pipes[0]);
  radio.openWritingPipe(pipes[1]);
  radio.setChannel(78);
  radio.setAutoAck(true); 
  radio.startListening();
}


void loop() {

  int len; 
  if(radio.available())
  {
  len = radio.getDynamicPayloadSize();
  radio.read(&datar, len);
  delay(5);
  Serial.println(datar);
  Wire.beginTransmission(7);
  Wire.write(&datar);
  Wire.endTran345smission();
  radio.printDetails();
  }
  delay(5);


}

Answer*

I think the answer is a combination of Nick and Mathieu's answers.

Like Nick said you haven't assigned any memory to datar, so this is probably causing a crash because of buffer overrun.  

Now to the call to read.  Mathieu said you are passing a pointer into the function when you probably didn't mean to.  But if you put Nicks change in then you **do** need to pass in a pointer to the character array.  You can do this by `radio.read(datar, len);` because the character array is a character pointer.  
You **do not** want to pass a pointer to a character pointer `&datar` because that would mean the function was able to move the memory that you have allocated.

Also, you need to prevent buffer overflows in the "new improved" code by checking that the value of `len` is less than or equal to the value you allocated when you declared the data buffer (i.e. 50).  Because you are using a number in two places you should declare it as a constant at the top of the file.

    const int MaxBufferSize = 50;
    char datar[MaxBufferSize];
    ...
    len = radio.getDynamicPayloadSize();
    if (len > MaxBufferSize)
      len = MaxBufferSize;
    radio.read(datar, len);

Hope that helps.

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