How to split a string using a specific delimiter in Arduino? - arduino

Question

I have a String variable and I want to extract the three substrings separeted by ; to three string variables.
String application_command = "{10,12; 4,5; 2}";
I cannot use substring method because this string can be like any of the following or similar patterns also.
String application_command = "{10,12,13,9,1; 4,5; 2}"
String application_command = "{7; 1,2,14; 1}"
The only thing that is common in these patterns is there are three sections separated by ;.
Any insight is much appreciated.
Thank you

Answer 1

I think you need a split-string-into-string-array function with a custom separator character.
There are already several sources on the web and at stackoverflow (e.g. Split String into String array).
// https://stackoverflow.com/questions/9072320/split-string-into-string-array
String getValue(String data, char separator, int index)
{
int found = 0;
int strIndex[] = {0, -1};
int maxIndex = data.length()-1;
for(int i=0; i<=maxIndex && found<=index; i++){
if(data.charAt(i)==separator || i==maxIndex){
found++;
strIndex[0] = strIndex[1]+1;
strIndex[1] = (i == maxIndex) ? i+1 : i;
}
}
return found>index ? data.substring(strIndex[0], strIndex[1]) : "";
}
You can use this function as follows (with ";" as separator):
String part01 = getValue(application_command,';',0);
String part02 = getValue(application_command,';',1);
String part03 = getValue(application_command,';',2);
EDIT: correct single quotes and add semicolons in the example.

Answer 2

The new SafeString Arduino library (available from the library manager) provides a number of tokenizing/substring methods without the heap fragmentation of the String class
See https://www.forward.com.au/pfod/ArduinoProgramming/SafeString/index.html
for a detailed tutorial
In this case your can use
#include "SafeString.h"
void setup() {
Serial.begin(9600);
createSafeString(appCmd, 50); // large enought for the largest cmd
createSafeString(token1, 20);
createSafeString(token2, 20);
createSafeString(token3, 20);
appCmd = "{10,12,13,9,1; 4,5; 2}";
size_t nextIdx = 1; //step over leading {
nextIdx = appCmd.stoken(token1, nextIdx, ";}");
nextIdx++; //step over delimiter
nextIdx = appCmd.stoken(token2, nextIdx, ";}");
nextIdx++; //step over delimiter
nextIdx = appCmd.stoken(token3, nextIdx, ";}");
nextIdx++; //step over delimiter
// can trim tokens if needed e.g. token1.trim()
Serial.println(token1);
Serial.println(token2);
Serial.println(token3);
}
void loop() {
}
Also look at pfodParser which parses these types of messages { } for use by pfodApp.

Answer 3

Do not forget to call delete[] to free the memory after the use of the array, that said here is my solution:
String* split(String& v, char delimiter, int& length) {
length = 1;
bool found = false;
// Figure out how many itens the array should have
for (int i = 0; i < v.length(); i++) {
if (v[i] == delimiter) {
length++;
found = true;
}
}
// If the delimiter is found than create the array
// and split the String
if (found) {
// Create array
String* valores = new String[length];
// Split the string into array
int i = 0;
for (int itemIndex = 0; itemIndex < length; itemIndex++) {
for (; i < v.length(); i++) {
if (v[i] == delimiter) {
i++;
break;
}
valores[itemIndex] += v[i];
}
}
// Done, return the values
return valores;
}
// No delimiter found
return nullptr;
}
Here is an example of how to use:
void loop() {
String test = "1,2,3,4,5";
int qtde;
String* t = split(test, ',', qtde);
for (int i = 0; i < qtde; i++) {
Serial.println(t[i]);
delay(1000);
}
delete[] t;
}