Programming Forums > Application Development > C++

LENIN · Feb 28th, 2008, 1:31 AM

I would like to derive a new ifstream class, that would ignore comments in a file (lines that start with a '#' character). For instance:

Input file (f.txt)

(Toggle Plain Text)

#This is a comment
This is not

An example of use

(Toggle Plain Text)

int main(){
  
  string a;
  commentStream cs("f.txt");

  if(!cs) exit(1);
  else{
     while(cs){
        cs >> a;
        cout << a << endl;
     }
  }
  return (0);
}

Expected output

(Toggle Plain Text)

This
is
not

I know I'm suppose to derive a new streambuf and than derive the new stream using this streambuf. But I can't figure out how the new streambuf should look like (which methods should be overridden and what should they do). I think I should override the underflow method but I'm not exactly sure how.

Any help would be welcome.

OpenLoop · Feb 28th, 2008, 10:37 AM

Why not create a separate read() function in your program that accepts the ifstream object pointer as input. The function can then read a line from the file, if it's a comment ignore it and get the next one, else return the read line.

Feb 28th, 2008, 1:31 AM	#1
LENIN Newbie Join Date: Dec 2005 Location: In the minds of all true communists. Posts: 15 Rep Power: 0	Deriving a new ifstream class I would like to derive a new ifstream class, that would ignore comments in a file (lines that start with a '#' character). For instance: Input file (f.txt) (Toggle Plain Text) #This is a comment This is not #This is a comment This is not An example of use (Toggle Plain Text) int main(){ string a; commentStream cs("f.txt"); if(!cs) exit(1); else{ while(cs){ cs >> a; cout << a << endl; } } return (0); } int main(){ string a; commentStream cs("f.txt"); if(!cs) exit(1); else{ while(cs){ cs >> a; cout << a << endl; } } return (0); } Expected output (Toggle Plain Text) This is not This is not I know I'm suppose to derive a new streambuf and than derive the new stream using this streambuf. But I can't figure out how the new streambuf should look like (which methods should be overridden and what should they do). I think I should override the underflow method but I'm not exactly sure how. Any help would be welcome. __________________ Science progresses one death at a time - Niels Bohr

Feb 28th, 2008, 10:37 AM	#2
OpenLoop Expert Programmer Join Date: May 2005 Location: East Lansing, MI Posts: 663 Rep Power: 4	Re: Deriving a new ifstream class Why not create a separate read() function in your program that accepts the ifstream object pointer as input. The function can then read a line from the file, if it's a comment ignore it and get the next one, else return the read line.

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Programming Forums > Application Development > C++

Deriving a new ifstream class