fold-line.c

/* Copyright © 2021-2023 Chee Bin HOH. All rights reserved.
 *
 * It splits a long lines into multiple line according to max limit per line.
 */

#include <libgen.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#define MAXLINE 80
#define BUFFERSIZE 1024

char *programName = NULL;

void printHelp(void) {
  fprintf(stderr, "%s [-h] [-m line]\n", programName);
  fprintf(stderr, "\n");
  fprintf(stderr, " -h      : print this help message\n");
  fprintf(stderr, " -m line : number of character per line [default is 80]\n");
}

int main(int argc, char *argv[]) {
  int c;
  int maxline = MAXLINE;
  int count = 0;
  int bufferUsed = 0;
  char buffer[BUFFERSIZE + 1] = {'\0'};

  programName = basename(argv[0]);

  while ((c = getopt(argc, argv, "m:")) != -1) {
    switch (c) {
    case 'm':
      maxline = strtol(optarg, NULL, 0);
      break;

    case '?':
    case 'h':
      printHelp();
      exit(1);
    }
  }

  while ((c = getchar()) != EOF) {
    if (bufferUsed < maxline) {
      buffer[bufferUsed++] = c;
      buffer[bufferUsed] = '\0';
    } else {
      char *cptr = &buffer[bufferUsed - 1];

      while (' ' != *cptr && cptr != buffer)
        cptr--;

      // the line input so far has no space, so we print everything out.
      if (buffer == cptr) {
        // I was taught to put variable definition before executable statement
        // in function block, but there will be time that I do not want to do
        // that when the variable definition is used so locally.
        for (int i = 0; i < bufferUsed; i++)
          putchar(buffer[i]);

        bufferUsed = 0;
        buffer[bufferUsed] = '\0';
      } else // the line input has space, so we print the line until space, and
             // then continue to build up line.
      {
        char *iter = buffer;

        while (iter != cptr) {
          putchar(*iter);
          iter++;
        }

        iter = buffer;
        cptr++;
        while (cptr != &buffer[bufferUsed]) {
          *iter = *cptr;
          iter++;
          cptr++;
        }

        *iter = '\0';
        bufferUsed = iter - buffer + sizeof(buffer[0]);

        putchar('\n');
      }

      buffer[bufferUsed++] = c;
      buffer[bufferUsed] = '\0';
    } /* if ( bufferUsed < maxline ) ... else */
  }   /* while ( ( c = getchar() ) != EOF ) */

  if (bufferUsed > 0) {
    int i = 0;

    while (i < bufferUsed) {
      putchar(buffer[i]);
      i++;
    }
  }

  return 0;
}