Make a reference in a method to the stream that I'm reading

Question

I'm in a method, named total_parsing, and I create a local variable istringstream stream(to_analize) (where to_analize is the string that I have to analyze).

When I reach the special char ( or [ I want to claim a method, reading_between_bracket, that read the string from the open bracket to the closing bracket. After that I want that the method reading_between_bracket give me the possibility to continue the reading in total parsing. I need a method for the reading of string in bracket because I want to claim it recursively every time I reach a bracket. The string is in the format of the example.

Example -( B + D -( ( G*F) -H )))

void total_parsing(string to_analize) {
  istrinstream stream(to_analize);
  do {
    // DO OTHER OPERATION WITHOUT BRACKET
    if (token == "(" || !token.find('(')) {
      stream = reading_between_bracket(stream);
    }
  } while (stream >> token);
}

istringstream reading_between_bracket(istringstream stream) {
  // DO THE OPERATION BETWEEN BRACKET
  // RECURSIVE CALL OF THIS METHOD IF I REACH A BRACKET,RETURN THE STREAM
  return stream(or a pointer that make possible to continue reading);
}

PS I have to use C++11 and I can utilize STL and sstream.

The code that is in description didn't work

showing code is guaranteed to match the code, a description of code is not. — Borgleader, Jul 13 '19 at 14:44

score 0 · Accepted Answer · answered Jul 13 '19 at 15:14

The code did not work because passing by value requires making a copy, and stringstream objects may not be copied. See also.

So instead, pass the stream by reference:

void parse(string input){
    istringstream stream(input);
    string token;
    while (stream >> token) {
        if (is_open_bracket(token)) {
            parse_inside_brackets(stream);
        }
    }
}

void parse_inside_brackets(istringstream& stream) {
    // notice the '&'
    // do some processing here; the stream's internal position is updated
    // there is no need to return anything; the change to `stream` will be
    // reflected in the caller
}

To accomplish the recursion you describe, you probably want something more like:

void parse(string input) { // helper function to set up recursion
    parse_rec(istringstream(input), 0);
}

void parse_rec(istringstream& stream, int level) {
    // 'level' param indicates how many nested brackets we've seen
    string token;
    while (stream >> token) {
        if (is_close_bracket(token) { return; }
        else if (is_open_bracket(token)) {
            parse_rec(stream, level + 1);
        }
        else {
            // handle token at this level
        }
    }
    // If we get here, we ran out of tokens. So if we're not at the base level...
    if (level) {
        // ... then we had an unmatched bracket, so do error handling
    }
}

(But it may be the case that you should read up on more sophisticated parsing techniques :) And on the other hand, if you can handle the task with this approach, then maybe you don't even need the recursion, just tracking of the indentation level.)

My problem is to read a operation like this -((((A + B)+ C) + D)*E) where bracket isn't separated by space — Rikissssss, Jul 13 '19 at 15:20
You will need a more sophisticated approach to *tokenizing* the stream, than simply using `>>`. Hopefully that term will help with your searches ;) — Karl Knechtel, Jul 14 '19 at 06:00

Make a reference in a method to the stream that I'm reading

1 Answers1