libplis Documentation

Introduction

plis is a C++ library of Perl Like Structures. It includes the string class plis::slip and its friend, the list class plis::llip (pronounced "yip"). For name protection these have been put in the namespace plis.

plis is based on the Splash library by Jim Morris, that was first described in the October 1993 issue of The C Users Journal (see http://www.wolfman.com/splash.html). The plis library is directly based on this library but with the following changes:

• Updated to use STL structures (string and dequeue) as its underlying base classes.

• Replaced the regular expression library with great PCRE library.

• Renamed the string and the list structures to slip and llip. (Ok, this might not have been a good idea. If you have a better idea for names please let me know!)

• Added support for more perl functions.

API documentation

• slip - The string class.
• llip - The list class.

Examples

Here are a few examples of some uses of plis.

The basic while loop

The following shows the basic prototype for a the perl while(<>) idiom. It is not very useful, but it may be used as a placeholder for more advanced parsing.

#include <fstream>
#include <plis.h>

using namespace std;
using namespace plis;

int main(int argc, char*argv[])
{
    fstream inf;
    slip S_;

    if (argc>1) 
        inf.open (argv[1], fstream::in);
    else 
        inf.open(0);

    while(inf >> S_) {
        S_.chomp();

        // skip comments
        if (S_.m("^#"))
            continue;

        // Place your own line based parsing here.

        cout << S_ + "\n";
    }
}

Command line parsing

The split() and the shift() commands make it very easy to parse the input, just like in perl. the slipprintf provides a printf compatible function that is sorely missing from the standard std::string function.

:
slip parse(slip command)
{
    llip cmds = command.split();
    int ntimes = 0;

    while(cmds) {
        slip S_ = cmds.shift();

        if (S_.m("^eat$")) {
            slip S_ = cmds.shift();
            return slipprintf("I like eating %s\n", (const char*)S_);
        }
        if (S_.m("^ntimes$")) {
            ntimes = cmds.shift().atoi();
            continue;
        }
        break;
    }
    return "ok";
}

Substitutions

Thanks to PCRE regular expressions work just like in perl! The following example shows a non-trivial conversion of a list of integers into a STL vector.

  // Read strings of ranges in perl syntax and build a vector<int> list.
  //
  // E.g. "1, 5, 6..9"
  //
  vector<int> slip_to_int_list(slip s)
  {
      vector<int> int_list;
      llip terms = s.split(",\\s*");

      while(terms) {
          plis term = terms.shift();
          llip match;
          
          if (term.m("^\\d+$", match)) {
              int_list.push_back(match[0].atoi());  // match[0] == $&
          }
          else if (term.m("^(\\d+)\\s*\\.\\.\\s*(\\d+)$", match)) {
              int i1 = match[1].atoi();   // match[1] == $1
              int i2 = match[2].atoi();
              for (int i=i1; i<=i2; i++) 
                  int_list.push_back(i);
          }
          else 
              die((slip) "Unknown string in list: " + term);
      }


      return int_list;
   }

More examples may be found in the test_library.cc program.

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plis - Perl Like Structures