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Currently I convert the characters in char received[20] to string using String randomString(received) and I am able to display it using Serial.println(randomString). After displaying the string, I would like to know the easiest way to clear out its contents.

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1  
Have a look at the related question at stackoverflow: stackoverflow.com/questions/632846/clearing-a-char-array-c ... – user3704293 Jan 11 at 12:07
    
Why are you converting a char array to a String just to print it? Do you realise just how bad that is for the poor little Arduino? hacking.majenko.co.uk/the-evils-of-arduino-strings – Majenko Jan 11 at 12:21
up vote 1 down vote

In C and C++ a null terminated array of characters is a string (although not a String). Many routines for reading input terminate the result with a null as does an assignment like"

char foo[] = "This is a string.";

All you would need to do to "clear" this string is to assign a null to the first character. For example:

foo[0] = '\0';
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This clears only the first byte. With = { 0 }; everything is cleared. – ott-- Jan 11 at 14:29
    
For C (null terminated) strings, if the first character is a null, then the string is empty or clear. Functionally that solves the problem, but if there are security concerns then you are right that the whole string should be cleared. – dlu Jan 11 at 15:15
up vote 0 down vote

First version with conversion from char[] to Arduino String class:

char received[20];
...
// Some code that assigns received
...
String randomString(received); 
Serial.println(randomString);

// Clear string
randomString = "";

Second version without the Arduino String class:

char received[20];
...
// Some code that assigns received
...
Serial.println(received);

// Empty received buffer
received[0] = 0;

And third version where the buffer is cleared:

char received[20];
...
// Some code that assigns received
...
Serial.println(received);

// Clear received buffer
memset(received, 0, sizeof(received));

Cheers!

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