Question about write() function

Using Arduino Programming Questions
1

Hello

I have little experience using the write() function, so is there any way to send the \r and \n terminals with it?

Thanks!

2

What are the ASCII values of '\r' and '\n' ?

Answer 13 and 10. So guess what your write() ?

3 
  write ('\r');
  write ('\n');
4

So I need to send a string via bluetooth that has terminals 10 and 13, using the write() function

This way I get an error:

  if (SerialBT.hasClient()) {
    SerialBT.write("page1\n\r");
    delay(10000);
    SerialBT.write("page2\n\r");
    delay(10000);
    SerialBT.write("page3\n\r");
    delay(10000);
  }

Is there any way to do this using write()?

5

Use print()?

6

I know using print() or println() does it. My question is if you can do the same thing using write()...

7

What problem are you trying to solve?

Definitions of the write() function from Print.h:

    virtual size_t write(uint8_t) = 0;
    size_t write(const char *str) {
      if (str == NULL) return 0;
      return write((const uint8_t *)str, strlen(str));
    }
    virtual size_t write(const uint8_t *buffer, size_t size);
    size_t write(const char *buffer, size_t size) {
      return write((const uint8_t *)buffer, size);
    }
8

Try "\r\n"

9

What error?

If you want "\r and \n terminals" in that order, try:
SerialBT.write("page1\r\n");

11

exit status 1
invalid conversion from 'const char*' to 'uint8_t {aka unsigned char}' [-fpermissive]

12

have you ever tried what was written in #3 on your own?

void setup() {
  Serial.begin(115200);
  Serial.print("text");
  Serial.write('\r');
  Serial.write('\n');
  Serial.print("anothertext");
}

void loop() {
  // put your main code here, to run repeatedly:
}

No?
describe exactly what's not working.
post your sketch. something we can put in the IDE and press compile. Not just a junk of some lines.
post the complete error message.

13

Are you using SofttwareSerial for "SerialBT"? It should inherit from Print and thus have "write(const char *str)". It looks like whatever your SerialBT is based on doesn't have that function. You should be able to work around that with:
SerialBT.write("page1\n\r", strlen("page1\n\r"));

Don't worry about having the string constant twice. The compiler will only keep one copy.

14

Yea, there's a whole lot fishy here, starting with OP motive for doing this.

Posting a complete code would help greatly. I highly suspect Pilot Error.

15

Here is the complete code:

#include "BluetoothSerial.h"

#if !defined(CONFIG_BT_ENABLED) || !defined(CONFIG_BLUEDROID_ENABLED)
#error Bluetooth is not enabled! Please run `make menuconfig` to and enable it
#endif

BluetoothSerial SerialBT;

void setup() {
  Serial.begin(9600);
  SerialBT.begin("ESP32test"); //Bluetooth device name
  Serial.println("The device started, now you can pair it with bluetooth!");
}

void loop() {
  if (Serial.available()) {
    SerialBT.write(Serial.read());
  }
  if (SerialBT.available()) {
    Serial.write(SerialBT.read());
  }
  delay(20);

  if (SerialBT.hasClient()) {
    SerialBT.write("page1\n\r", strlen("page1\n\r"));
    delay(10000);
    SerialBT.write("page2\n\r", strlen("page3\n\r"));
    delay(10000);
    SerialBT.write("page3\n\r", strlen("page3\n\r"));
    delay(10000);
  }
  else {
    Serial.println("NOT C");
  }
}

Also shows error:

exit status 1
invalid conversion from 'const char*' to 'const uint8_t* {aka const unsigned char*}' [-fpermissive]

16

Great. Now tell us why you're so fixated on using write() instead of print().

17

That is far from complete.
Is it for a ESP32 board ? And you are using the Espressif Bluetooth library ?
If you turn on the extra compiler output, then the compile will tell a lot more.
For example:

/sketch/sketch.ino: In function 'void loop()':
/sketch/sketch.ino:25:20: error: invalid conversion from 'const char*' to 'const uint8_t*' {aka 'const unsigned char*'} [-fpermissive]
     SerialBT.write("page1\n\r", strlen("page1\n\r"));
                    ^~~~~~~~~~~

As @johnwasser wrote in Reply #13, the Bluetooth library is not fully compatible. The const char * is missing here.

Things you can do:

  1. Fix it yourself with SerialBT.write((const uint8_t *)"page1\r\n", strlen("page1\r\n"));
  2. Make an Issue at Github and request that a const char * will also work.
  3. Use normal code, just like everyone else. For example: SerialBT.println("page1"); The .println() function writes the text and add the CarriageReturn and LineFeed.

This is bold text to get your attention, I can make it red as well: It is "\r\n" not "\n\r".

18

I see the reason. BluetoothSerial.h doesn't pull in the required function definitions from Print.h by including:

using Print::write;

Compare BluetoothSerial.h to HardwareSerial.h (for an AVR board) and you'll see this.
Said functions are not declared 'virtual' in Print.h so they're not inherited from Print via Stream.

1 Like
19

I have added the links in this quote ▲

Well spotted.
The .print() and .println() work, so a normal text string is no problem.

1 Like
20

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