Problem with substring

Troubleshooting
1

In trying to use the String class function substring, I get the following error:

undefined reference to `String::operator=(String&&)’

I suspect this is caused by a bug in the implementation of this in the String class, so I have simplified the problem into a few code lines so everyone can experience it / troubleshoot themselves, just attempt to verify this code to reproduce the error:

void setup() {
    Serial.begin(9600);
    String myString;
    String mySubstring;
    myString = "1. This is a test string";
    mySubstring = myString.substring(4,18);
    Serial.println(mySubstring);
}
void loop() { }
2

It has been my experience that you need to define the new string as a string with the substring.

try
String mySubstring = myString.substring(4,18);

1 Like
3

Thanks for the input, but while that does work in the code excerpt that I posted, the compiler does not like re-declaring variables, so that would not let me use it as an actual variable such as:

void setup() {
    Serial.begin(9600);
    String myString;

    myString = "1. This is a test string";
    myString2 = "2. This is also a test string";

    String mySubstring = myString.substring(4,18);
    Serial.println(mySubstring);

    String mySubstring = myString2.substring(4,23);
    Serial.println(mySubstring);
}
void loop() { }

This does actually work in the code where I am implementing this. In my case it creates a new value for the mySubstring variable in every iteration of a loop, unfortunately it does require that the variable is re-declared every iteration as well which at the very least is messy… but it does work.

I do appreciate the input, it allows me to continue until the implementation of the String class is fixed.
Thanks!

4

The code for that operator in the String class is commented out with an #ifdef for an experimental version of the C compiler. I don’t know why, but I suspect it does not work in the current compiler.

The best way I have found to deal with this is set the string to empty and then concatenate.

mySubString = "";
mySubString += myString.substring(4,18);

Concatenate always copies data from one String to another, while the original code is trying to change the pointer for mySubString to point to a new instance of String.

4 Likes
5

@bko Thank you for that! Funny that @iiiman thought it was a bug, and I thought I was just my niavete’ in understanding the correct syntax - LOL!

2 Likes