Using stringstream to indent/center output

Question

I'm learning c++ and got the project to send a pascal's triangle to output (after n-rows of calculation)., getting output like this, stored in a stringstream "buffer"

 1
 1 1
 1 2 1
 1 3 3 1

But what I want is rather

    1
   1 1
  1 2 1
 1 3 3 1

My idea was: calculate the difference of the last line and current line length (I know that the last one is the longest). Then pad each row using spaces (half of the line-length-difference). My Problem now is:

• I didn't get how getLine works, neither how I might extract a specific (-> last) line
• I don't know and could not find how to edit one specific line in a stringstream

Somehow I got the feeling that I'm not on the best way using stringstream.

So this is rather a common question: How'd you solve this problem and if possible with stringstreams - how?

Davilman

cplusplus.com/reference/iostream/manipulators/setw take a look a this – Unwritten

Just to be clear, are you calculating the values your self and printing? Or are you parsing them and then reprinting? – Conspectus

I calculate them myself, I'm gonna have a look at setw, seems to be a nice way :-) – Davilman

This works very nice but unfortunately I've got my whole triangle stored already in a stringstream (called buffer). setw() is only able to set the width for the current line. How can I set the line with persisting? – Davilman

Okay I found out that this isn't possible in an easy way (overloading the << operator is no option here :D). So I decided to read my stringstream out line by line again (using getline) – Davilman

Answer 1

To know the indentation of the first line, you would need to know the number of lines in the input. Therefore you must first read in all of the input. I chose to use a vector to store the values for the convenience of the .size() member function which will give the total number of lines after reading in all input.

#include<iostream>
#include<sstream>
#include<vector>
#include<iomanip> // For setw
using namespace std;
int main()
{
  stringstream ss;
  vector<string> lines;
  string s;

  //Read all of the lines into a vector
  while(getline(cin,s)) 
    lines.push_back(s);

  // setw() - sets the width of the line being output 
  // right  - specifies that the output should be right justified 
  for(int i=0,sz=lines.size();i<sz;++i)
    ss << setw((sz - i) + lines[i].length()) << right << lines[i] << endl;

  cout << ss.str();
  return 0;
}

In this example, I am using setw to set the width of the line to be right justified. The padding on the left side of the string is given by (sz - i) where sz is the total number of lines and i is the current line. Therefore every subsequent line has 1 less space on the left hand side.

Next I need to add in the original size of the line (lines[i].length()), otherwise the line will not contain a large enough space for the resulting string to have the correct padding on the left hand side.

setw((sz - i) + lines[i].length())

Hope this helps!

Abad

Answer 2

If you have access to the code that writes the initial output, and if you know the number of lines N you are writing, you could simply do:

for(int i = 0; i < N; ++i) {
    for(int j = 0; j < N - 1 - i; ++j)
        sstr << " "; // write N - 1 - i spaces, no spaces for i == N.
    // now write your numbers the way you currently do
}

Biologist

i doubt it will work when N increases and double digit numbers come into play. Will it? – Atonic

@Atonic Sure, you would need to compute width = max(choose(N,k) % 10 to get the number of digits, and write (N - 1 - i) * width whitespaces. My point simply was that it's easier to combine formatting with the computation, rather than to format output after the computation. – Biologist

somehow I'd find it nicer to first compute the values and then format the output... – Davilman

So go read the stringstream getline reference: cplusplus.com/reference/iostream/istream/getline – Biologist