How to convert String to byte array

Question 1

I have the code, it's purpose is to receive the string from a comport like:Set@1234567890123456@1234567890123456@1234567890123456@1234567890123456and translate it into four byte arraysbyte user1[16], user2[16], pass1[16], pass2[16]. Here's the code:

String inString = ""; // COM port incoming data buffervoid setup() {  // put your setup code here, to run once:  Serial.begin(9600);  Serial.println("Start");}void loop() {  // put your main code here, to run repeatedly:  // Receive data from com port  while (Serial.available() > 0) {    int inChar = Serial.read();    if (inChar != '\n') {      inString += (char)inChar;    } else {      // New line      String Action = inString.substring(0, 3);      if (Action == "Set") {        SetCard(inString);      } else if (Action == "Get") {        Serial.println("1");      } else {        Serial.println(Action);      }      inString = "";    }  }}void SetCard(String Data) {  Serial.println(Data);  // Data Set@user1@user2@pass1@pass2  // Set@1234567890123456@1234567890123456@1234567890123456@1234567890123456  byte user1[16], user2[16], pass1[16], pass2[16];  String user1str = inString.substring(4, 20);  String user2str = inString.substring(21, 37);  String pass1str = inString.substring(38, 54);  String pass2str = inString.substring(55, 71);  Serial.println("Strings");  Serial.println(user1str);  Serial.println(user2str);  Serial.println(pass1str);  Serial.println(pass2str);  Serial.println("Arrays");  user1str.getBytes(user1, 16);  user2str.getBytes(user2, 16);  pass1str.getBytes(pass1, 16);  pass2str.getBytes(pass2, 16);  writeByteArray(user1, 16);  writeByteArray(user2, 16);  writeByteArray(pass1, 16);  writeByteArray(pass2, 16);}void writeByteArray(byte array[], int arrlength){  for (int j = 0 ; j < arrlength ; j++) //print the block contents  {    Serial.write (array[j]);//Serial.write() transmits the ASCII numbers as human readable characters to serial monitor  }  Serial.println("");}

When I run this code and send my string through a com port I expect the output:

StartSet@1234567890123456@1234567890123456@1234567890123456@1234567890123456Strings1234567890123456123456789012345612345678901234561234567890123456Arrays1234567890123456123456789012345612345678901234561234567890123456

And yet, I receive

StartSet@1234567890123456@1234567890123456@1234567890123456@1234567890123456Strings1234567890123456123456789012345612345678901234561234567890123456Arrays123456789012345123456789012345123456789012345123456789012345

Why? And how do I receive desired output?getBytes docs

Question 2

Why? And how do I receive desired output? getBytes docs

The String member functiongetBytes() will null-terminate the string. You must add space for that.

  byte user1[17], user2[17], pass1[17], pass2[17];  ...  user1str.getBytes(user1, sizeof(user1));  ...  Serial.print((char*) user1);

That should do the trick.

Question 3

Thank you. It worked. So, how can I truncateuser1[17] array touser1[16] after I set it value with getBytes?

Question 4

Or do I need to create a buffer array[17] and then write the first 16 elements from there to array[16]?

Question 5

Come to think of it I could justfor (int j = 0 ; j < sizeof(user1) ; j++) { user1[j] = user1str.charAt(j); } and it would work with 16 elements

Question 6

Using String.getBytes(buffer, len) to get bytes.

"len" is the length to copy, but usually need to add 1 for the end of string '\0'.

For example:

String s = "123";int count = s.length();  // lenth() is 3s.getBytes(buffer, count);   // copied "12\0" => HEX(31 32 00)s.getBytes(buffer, count + 1);   // copied "123\0" => HEX(31 32 33 00)

The official document not mentioned those above, and it's not reasonable for the modern function design.

Misunderstanding in that and waste our life so much.

Question 7

toCharArray() is documentedarduino.cc/reference/en/language/variables/data-types/string/…

Question 8

toCharArray(buffer, len) will still keep the last bye for 0x00 ('\0'). So if want to copy the specific length of the content, len should add 1 for '0'. Also, care the buffer length as the last damn byte.

Question 9

that is what is expected for char-array (C string) (but not expected for getBytes)

Question 10

If the official document has mentioned the '\0' in details, it's fine for purpose. It's pity for none.

Question 11

I am heaving difficulties reading your post and comments. How do you declarebuffer?

Mikael Patel 7,9892 gold badges16 silver badges21 bronze badges · Accepted Answer · 2016-03-15 20:02:48Z

2

Why? And how do I receive desired output? getBytes docs

The String member functiongetBytes() will null-terminate the string. You must add space for that.

  byte user1[17], user2[17], pass1[17], pass2[17];  ...  user1str.getBytes(user1, sizeof(user1));  ...  Serial.print((char*) user1);

That should do the trick.

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answeredMar 15, 2016 at 20:02

Mikael Patel

7,9892 gold badges16 silver badges21 bronze badges

3

Thank you. It worked. So, how can I truncateuser1[17] array touser1[16] after I set it value with getBytes?
rfg
– rfg
2016-03-15 20:08:39 +00:00
CommentedMar 15, 2016 at 20:08
Or do I need to create a buffer array[17] and then write the first 16 elements from there to array[16]?
rfg
– rfg
2016-03-15 20:10:24 +00:00
CommentedMar 15, 2016 at 20:10
Come to think of it I could justfor (int j = 0 ; j < sizeof(user1) ; j++) { user1[j] = user1str.charAt(j); } and it would work with 16 elements
rfg
– rfg
2016-03-15 20:13:23 +00:00
CommentedMar 15, 2016 at 20:13

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