I'm trying to use nRF24L01 module to send a messages between 2 arduinos

Transmiter code:

  const char text[] = "Hello World";
  radio.write(&text, sizeof(text));


Reciver code:

char text[32] = {0};
radio.read(&text, sizeof(text));


How I can put into char array an int value? I tried doing it in this way

For example: int a = 60; const char text[] = String(a); radio.write(&text, sizeof(text));

  • 1
    radio.println(a) maybe? Jul 7, 2016 at 18:31

3 Answers 3


Are you just looking for a way to get an arbitrary number expressed as a string? If so, you'll likely want to use some existing functions to help you along.

I recommend using sprintf

sprintf(char * str, char * format, args)

Where str is the string you're storing results in, format is the string you're inserting your values into for, you guessed it, formatting, and args are all the args, separated by commas, that you'll be passing into the format string to be inserted into the str string. An example might be:

char[x] result;    //x is the number of elements in your array, atleast one for every letter and one for the end character, ex: "hello" needs 6.
int number = 24;
sprintf(result, "My number is %d", number);
sendSomewhere(result);   //sends "My number is 24"
  • 1
    You forgot to declare the size of result. Also, if your “somewhere” inherits from Print (most things that implement write() do), then you can somewhere.print("My number is "); somewhere.print(24);. Jul 8, 2016 at 12:12
  • I did forget to declare a size for result! for OP, that line should read "char[x] result" where x is the number of elements in your char array. As for sendSomewhere(result), it was just supposed to be an open-ended function for the OP to get the concept with. Jul 8, 2016 at 23:54
  • 1
    1) By char[x] result; you probably mean char result[x];. 2) I understand the virtues of an open-ended answer, but using sprintf() instead of Print::print() will make the compiled program grow by 1 K or so. If the program already uses Print::print() (which is likely, since it is so common in Arduinoland), then the cost of sprintf() is more like 1.5 K. Jul 9, 2016 at 13:08
  • 1
    sprtintf() returns the length of the string created so you can do int length=sprintf(result, "My number is %d", number); radio.write(result, length); This saves using strlen() to calculate how many bytes to send.
    – Andrew
    Oct 7, 2016 at 8:02

You can not have 'const' prefixed the 'text' variable as it then become 'read-only'.

    char text[32];
    int a = 60;
    sprintf(text, "Number %d", a);
    radio.write(&text, sizeof(text));

The simplest method is to send the integer in binary format (skipping the conversion to text).

int a = 60; 
radio.write((char*) &a, sizeof(a));


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