Passing/printing parameters in Arduino - arduino

Question

There is a function RFID that returns *z4 parameter that should be put into TagID.
When I print TagID from loop(), '1' instead of '1B31687DBC7FF' is printed.
How can I get the whole value? I would like to print full string '1B31687DBC7FF' to serial port.
#include "Arduino.h"
#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
LiquidCrystal_I2C lcd(0x3F, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);
int inWord = 0;
int outWord[] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
int index = 0;
unsigned char Data2Calc[]= { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
unsigned short CRC2Calc = 0;
unsigned char Bytes2Calc = 9;
char z5 []= { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
const char* TagID;
void setup()
{
pinMode(13, OUTPUT);
lcd.begin(16,2);
lcd.backlight();
lcd.setCursor(0,0);
lcd.print("RFID Reader");
lcd.setCursor(0,1);
lcd.print("Skanuj TAG");
Serial.begin(9600);
Serial1.begin(9600);
lcd.setCursor(0,0);
}
void loop()
{
if (Serial1.available())
{
TagID = RFID();
}
else
{
if (index==11)
{
index=0;
Serial.print(TagID);
Serial.println("");
lcd.setCursor(0,0);
lcd.print("ID:");
lcd.print(TagID);
}
}
}
const char * RFID()
{
char z1 []= { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
char z2 []= { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
char z3 []= { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
unsigned short crc2[] = { 0 };
inWord = Serial1.read();
index++;
if (index == 1)
{
if (inWord == 1)
{
outWord[index] = inWord;
}
else
{
index=index-1;
}
}
else if (index > 1)
{
if (index == 11)
{
outWord[index] = inWord;
for (int i = 1; i <12; i++)
{
Data2Calc[i-1] = outWord[i];
}
CRC16(Data2Calc, &CRC2Calc, Bytes2Calc);
itoa(outWord[10],z1,16);
itoa(outWord[11],z2,16);
strcat(z1, z2);
*crc2 = CRC2Calc;
sprintf(z2, "%x", *crc2); //
if (strcmp(z1,z2) == 0)
{
char z4 []= { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
for (int i=1;i<10;i++)
{
itoa(outWord[i],z3,16);
if (strlen(z3)<2) strcat(z4, "0");
strcat(z4, z3);
//Serial.print(z4);
//Serial.println("");
}
//Serial.print("z4=");
//Serial.print(z4);
//Serial.println("");
strncpy(z5, z4, 18);
}
}
else
{
outWord[index] = inWord;
}
}
return z5;
}
void CRC16(unsigned char * Data, unsigned short * CRC, unsigned char Bytes)
{
int i, byte;
unsigned short C;
*CRC = 0;
for (byte = 1; byte <= Bytes; byte++, Data++)
{
C = ((*CRC >> 8) ^ *Data) << 8;
for (i = 0; i < 8; i++)
{
if (C & 0x8000)
C = (C << 1) ^ 0x1021;
else
C = C << 1;
}
*CRC = C ^ (*CRC << 8);
}
}
Whole output of the functions is attached bellow:
Currently there are no serial ports registered - please use the + button to add a port to the monitor.
Connect to serial port COM4 at 9600
TagID: 1
UPDATE 1
I have attached above full code. Sorry... it is a bit long.
UPDATE 2
OK. I got it somewhat working, but not quite as expected. I got the value printed as expected, but only for the first time I call the function. If I call the function more times, I get some garbage added to the printed value as bellow:
Currently there are no serial ports registered - please use the + button to add a port to the monitor.
Connect to serial port COM4 at 9600
TagID: 1b31596d9cff
TagID: 1b31596d9cff1b31596d9cff
TagID: 1b31596d9cff1Řc–
ś˙cŘ1b31596d9cff
TagID: 1b31596d9cff1Řc–
ś˙cŘ1b311031596d9cff
TagID: 1b31596d9cff1Řc–
ś˙cŘ1b311031596d9cff
Any idea on what the problem might be?
I have updated the latest full source code at the top of the post.
Thanks.
UPDATE 3
OK, I got it finally working. I have changed declaration from 'char z1 []=...' to 'const char z1 []=...'
I am not sure it is written in decent style... but it works :) I attach working source code at the top of the page.
UPDATE 4
No, after a few tests I have to admit that the solution from UPDATE 3 does NOT work. Indeed it reads correctly but only for the first time... then program crashes and... it reads RFID again for the first time... so it looks only it reads OK, but it does not.
Serial output for 5 readings is as follows:
Currently there are no serial ports registered - please use the + button to add a port to the monitor.
Connect to serial port COM4 at 9600
1b31596d9cff
1b31596d9cff1b31596d9cff
1b31596d9cff1Řc–
ś˙cŘ1b31596d9cff
1b31596d9cff1Řc– ś˙cŘ1b311031596d9cff
1b31596d9cff1Řc– ś˙cŘ1b311031596d9cff
Any hints on what is wrong with the code?
UPDATE 5
OK. Finally I got it working... at least from what I can see.
I changed tables size, reworked HEX display way and made a few minor changes.
The entire source code updated at the top.

Answer 1

TagID is a char and your function returns a char. A char is a one byte variable. It will hold at most one character. It shouldn't then surprise you that you only print one character. You haven't provided enough of your code to really figure out what you're actually after. But that explains why you only get one character printed. A char variable can hold one character, not that whole string of stuff.
I'm thinking that you wanted to get a char*, a pointer to a char array. But you're going to have trouble with that too because z4 is a local array and goes out of scope before you get a chance to use it.