Check the "strcmp" which came to buffer

Projects Programming
1

Hello!

Arduino is connected to the computer. The keyboard enters the word "on" to light the diode, and the word "off" to turn off the LED. I used the "readBytesUntil," and to check what came to buffer the "strcmp". I wrote code

  int led = 13; 
  
  void setup()
  {
     pinMode(led, OUTPUT); 
     Serial.begin(9600);
     Serial.flush();
  }
 
  void loop()
  {
     char buf[4];
     byte nb;
     nb=Serial.readBytesUntil('\n',buf,4);

     String input = "";
 
     while (Serial.available() > 0)
     {
         input += (char) Serial.read(); 
         delay(5); 
     }
 
     if (strcmp(nb, "on") == 0) 

     {
         digitalWrite(led, HIGH); 
     }
     else if (strcmp(nb, "off") == 0)
     {
         digitalWrite(led, LOW); 
     }
 }

The code does not compile because:

sketch_nov24a.ino: In function ‘void loop()’:
sketch_nov24a.ino:25:25: error: invalid conversion from ‘byte {aka unsigned char}’ to ‘const char*’ [-fpermissive]
In file included from /usr/share/arduino/hardware/arduino/cores/arduino/Arduino.h:5:0,
                 from sketch_nov24a.ino:2:
/usr/lib/avr/include/string.h:125:12: error:   initializing argument 1 of ‘int strcmp(const char*, const char*)’ [-fpermissive]
 extern int strcmp(const char *, const char *) __ATTR_PURE__;
            ^
sketch_nov24a.ino:30:31: error: invalid conversion from ‘byte {aka unsigned char}’ to ‘const char*’ [-fpermissive]
In file included from /usr/share/arduino/hardware/arduino/cores/arduino/Arduino.h:5:0,
                 from sketch_nov24a.ino:2:
/usr/lib/avr/include/string.h:125:12: error:   initializing argument 1 of ‘int strcmp(const char*, const char*)’ [-fpermissive]
 extern int strcmp(const char *, const char *) __ATTR_PURE__;
            ^

How to improve the above code?

2 
extern int strcmp(const char *, const char *) __ATTR_PURE__;

The error message is telling you that argument 1 to strcmp must be a pointer to a character string. You have supplied a character '\n'. Use "\n" instead.

Pete

4

Get rid of the String variables...they waste too much memory and usually are not worth the "convenience". For example, try:

  int led = 13; 
  
  void setup()
  {
     pinMode(led, OUTPUT); 
     Serial.begin(9600);
     Serial.flush();
  }
 
  void loop()
  {
     char buf[4];
     int charsRead;
     
 
     while (Serial.available() > 0)
     {
       charsRead = Serial.readBytesUntil('\n', buf, 4);
       buf[charsRead] = '\0';                                       // Make it a string
     }
 
     if (strcmp(buf, "on") == 0) 
     {
         digitalWrite(led, HIGH); 
     }
     else if (strcmp(buf, "off") == 0)
     {
         digitalWrite(led, LOW); 
     }
 }
5

Have a look at the examples in Serial Input Basics - simple reliable ways to receive data.

If you really just want to control ON and OFF just send the single character 'N' or 'F' - it will make the Arduino code very much simpler.

...R

6 
     Serial.begin(9600);
     Serial.flush();

Start the serial connection, and then immediately wait until all pending outgoing serial data has been sent. Here's a clue. There is NONE. The flush() is useless. Get rid of it.

7

Thank you for all your help.