Software Tools source code

Autor: Andre Adrian
Version: 31.may.2011

Introduction

The book "Software Tools" was written in 1976 by Brian W. Kernighan and P. J. Plauger. For a C programmer it is wise to read all books that were co-authored by Kernighan. In "Software Tools" the authors used the programming language RATFOR. RATFOR was implemented as a FORTRAN pre-processor. For easy digestion of the pearls of programming wisdom in this book, the source code was ported (transcribed) from RATFOR to ANSI-C. Beginners in the area of programming shall start with the C-tutorial, another document by Kernighan, which is now available for ANSI-C.
Computer science is still a new department at an university. The first computer science historians begin now to preserve the early heritage of the field. One of these private preservation actions is to bring again to life the source code from the book "Software tools".

Contents

detab - Removing Tabs

The program detab is presented in chapter 1.5, Removing Tabs, starting at page 18.

#include <stdio.h>

enum {
   MAXLINE = 100,
   YES = 1,
   NO = 0,
   TAB = 9,
   NEWLINE = 10,
   BLANK = 32,
};

/* tabpos -- return YES if col is a tab stop */
int tabpos(int col, int tabs[])
{
   if (col >= MAXLINE)
      return YES;
   else
      return tabs[col];
}

/* settab -- set initial tab stops */
void settab(int tabs[])
{
   int i;

   for (i = 0; i < MAXLINE; i = i + 1)
      if (1 == i % 8)
         tabs[i] = YES;
      else
         tabs[i] = NO;
   return;
}

/* detab -- convert tabs to equivalent number of blanks */
int main()
{
   int c;
   int col, tabs[MAXLINE];

   settab(tabs);                /* set initial tab stops */
   col = 1;
   while ((c = getchar()) != EOF)
      if (TAB == c)
         do {
            putchar(BLANK);
            col = col + 1;
         }
         while (tabpos(col, tabs) != YES);
      else if (NEWLINE == c) {
         putchar(NEWLINE);
         col = 1;
      } else {
         putchar(c);
         col = col + 1;
      }
   return 0;
}

entab - Putting Tabs Back

The program entab is presented in chapter 2.1, Putting Tabs Back, starting at page 35.

#include <stdio.h>

enum {
   MAXLINE = 100,
   YES = 1,
   NO = 0,
   TAB = 9,
   NEWLINE = 10,
   BLANK = 32,
};

/* tabpos -- return YES if col is a tab stop */
int tabpos(int col, int tabs[])
{
   if (col >= MAXLINE)
      return YES;
   else
      return tabs[col];
}

/* settab -- set initial tab stops */
void settab(int tabs[])
{
   int i;

   for (i = 0; i < MAXLINE; i = i + 1)
      if (1 == i % 8)
         tabs[i] = YES;
      else
         tabs[i] = NO;
   return;
}

/* entab -- replace blanks by tabs and blanks */
int main()
{
   int c;
   int col, i, newcol, tabs[MAXLINE];

   settab(tabs);
   col = 1;
   for (;;) {
      newcol = col;
      while (BLANK == (c = getchar())) {        /* collect blanks */
         newcol = newcol + 1;
         if (YES == tabpos(newcol, tabs)) {
            putchar(TAB);
            col = newcol;
         }
      }
      for (; col < newcol; col = col + 1)
         putchar(BLANK);        /* output leftover blanks */
      if (EOF == c)
         break;
      putchar(c);
      if (NEWLINE == c)
         col = 1;
      else
         col = col + 1;
   }
   return 0;
}

About the author

The author is a computer science engineer of the second generation. He did not learn the programming language C on a PDP11 with the AT&T compiler cc in the 1970s, but in the 1980s on an Atari ST with the Lattice C compiler. Interest in the history of computer science is only a hobby, for his living the author maintains and creates state of the art software. Today, many people call it progress if things are done different. For the author, progress is to do things better. Doing things better is much harder then doing things different. To make things better, it helps to look into the past and learn from the engineers that worked in the field before yourself.