If i am not going to modify a string then is the first option better or are both same- (I just want to iterate through the string, but since string size is big I don't want local copy to be made.) 

int getString(string& str1) {
    //code
}


int getString (string str1) {
    //code
}

And if I do plan on changing the string, then is there any difference between the two? Is it because strings are immutable in C++?

c++ string parameters reference
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