Slice string at ":"

Question

I need to slice a string (eg- 4:288:18464:288:4) at ":" into an array({4, 288, 18464, 288, 4}) I used the following code, but its giving only '4' in the serial monitor when "4:288:18464:288:4," is given to arduino.

void displayString(char* s)
{
 char* text = strtok(s,":");
 while(text != NULL){
 text = strtok(NULL,":");}
}
void loop()
{
 if(Serial.available() > 0)
 {
 str = Serial.readStringUntil(',');
 str.toCharArray(text,99);
 }
 displayString(text);
Serial.println(text);
}

• jfpoilpret: Do you know in advance how many substrings you expect from the original one?
• user3826856: Every string will contain 5 substring. But the number of strings will be different each time.

Answer 1

You don't use strtok the way it should:

char* text = strtok(s,":");
while(text != NULL){
 text = strtok(NULL,":");
}

Your code just replaces, in s, all occurrences of : with 0 (i.e. a byte of value 0, not the ASCII value of '0'), thus terminating each substring.

At the end of displayString(text) call from loop(), text still points to the 1st character of the original string (in your post 4:288:18464:288:4), but that string now terminates at the position of the first :, which explains why Serial.println(text) prints just 4.

Now if you want to split the original string into an array of substrings, as asked in your question, you need to modify displayString this way:

// Maximum number of substrings expected
const int MAX_SUBSTRINGS = 5;
// Array of pointers to each substring after displayString() has been called
static char* substrings[MAX_SUBSTRINGS];
void displayString(char* s) {
 // First clear the array of substrings
 for (int i = 0; i < MAX_SUBSTRINGS; i++)
 substrings[i] = 0;
 // Now split the input string
 char* text = strtok(s,":");
 int i = 0;
 while (text != 0 && i < MAX_SUBSTRINGS) {
 // A toekn was found: append it to the array of substrings
 substrings[i++] = text;
 text = strtok(0,":");
 }
}

After calling displayString(text), you can use its result in loop() as follows:

void loop()
{
 if (Serial.available() > 0)
 {
 str = Serial.readStringUntil(',');
 str.toCharArray(text,99);
 }
 displayString(text);
 for (int i = 0; i < MAX_SUBSTRINGS; i++) {
 if (substrings[i] != 0)
 Serial.println(substrings[i]);
 }
}

Note that this will work ONLY if the original string contains no more than 5 substrings delimited by :. If the max number of substrings cannot be known at compile time, then you'll have to use dynamic allocation, which is generally not a very good idea on embedded platforms.