How convert string to byte[]? - arduino

Question

I have Arduino + Ethenet shield. I want to dynamically change the ip depending on that will come at the input com-port.
The main problem is - input string has a String type, and Ethernet.begin method accepts a byte array. In general, I can not understand how to convert this string correctly. Tried to make a bicycle(crutch) by moving the string in the char array, and then in the byte array. Did not work out. How convert string to byte[]?
#include <SPI.h>
#include <Ethernet.h>
String readString;
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED }; //physical mac address
byte myserver[] = { 208, 104, 2, 86 }; // zoomkat web page server IP address
EthernetClient client;
void initEthernetConfig(byte ip[])
{
Ethernet.begin(mac, ip);
Serial.begin(9600);
Serial.println("Better client test 12/01/11"); // so I can keep track of what is loaded
Serial.println("Send an e in serial monitor to test"); // what to do to test
}
void setup(){
byte ip[] = { 10, 28, 33, 4 };
// initEthernetConfig(ip);
}
void loop(){
// check for serial input
while (Serial.available()) {
char c = Serial.read(); //gets one byte from serial buffer
readString += c; //makes the String readString
delay(2); //slow looping to allow buffer to fill with next character
}
if (readString.length() >0) {
byte inArray[4];
char * tokens;
int i = 0;
tokens = strtok(readString, ".");
while (tokens != NULL) {
inArray[i] = atoi(tokens);
tokens = strtok(NULL, ".");
i++;
}
initEthernetConfig(inArray);
}
}

Answer 1

This is a possible solution, it parses, dumps and sets an IPv4:
#include <SPI.h>
#include <Ethernet.h>
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED }; //physical mac address
byte myserver[] = { 208, 104, 2, 86 }; // zoomkat web page server IP address
EthernetClient client;
/**
* help functions declaration
*/
void get_ip(byte ip[4]);
void dump_ip(byte ip[4]);
void initEthernetConfig(byte ip[]);
/**
* setup && loop
*/
void setup(){
Serial.begin(9600);
}
void loop()
{
byte ip[4];
get_ip(ip);
dump_ip(ip);
initEthernetConfig(ip);
}
/**
* help function implementation
*/
void get_ip(byte ip[4])
{
for (byte i = 0; i < 4; ++i) {
while (Serial.available() <= 0) { };
ip[i] = (byte) Serial.parseInt();
if (i < 3) { Serial.read(); } // throw away dot
}
};
void dump_ip(byte ip[4]) {
for (byte i = 0; i < 4; ++i) {
Serial.print(ip[i]);
if (i < 3) {
Serial.print('.');
} else {
Serial.println();
}
}
};
void initEthernetConfig(byte ip[])
{
Ethernet.begin(mac, ip);
Serial.println("Better client test 12/01/11"); // so I can keep track of what is loaded
Serial.println("Send an e in serial monitor to test"); // what to do to test
};
Obviously, outside this testing application you should ensure that the Serial input is ready for sending an IPv4 in the first place, otherwise the function will likely return 0.0.0.0. An idea would be to enrich your communication protocol with string-based commands, e.g. ip: would signal the start of an IPv4 input.

Answer 2

Try this:
while (tokens != NULL) {
inArray[i++] = atoi(tokens) & 0xFF;
tokens = strtok(NULL, ".");
}
Which will get only the last byte of the integer, but that is all you want in the case of values 0-255.
But then again why not just read it in as bytes...
void loop(){
byte inArray[4];
int i = 0;
// check for serial input
while (Serial.available()) {
inArray[i++] = (byte) Serial.read(); //gets one byte from serial buffer
delay(2); //slow looping to allow buffer to fill with next character
}
initEthernetConfig(inArray);
}