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Quest: page 30​

Revise the main routine of the lonigest-line program so it will correctly print the length of arbitrarily long input lines, and as much as possible of the text.

I understood this problem like this:

  • count characters longer than the defined 1000 and then print 1000 order more characters of that input. i've chosen unsigned long int which has the max value of (1 << 64) -1.

gen test data​

note

i wrote two lines in the txt file.

  • line one: 65535 chars long
  • line two: 100 chars long
#include <stdio.h>
#include <stdlib.h>

#define MAX 0xFFFF

int main() {
  FILE *f = fopen("txt", "w");
  if (f == NULL) {
    return EXIT_FAILURE;
  }
  // printf w MAX times
  for (unsigned short i = 0; i < MAX; i++) {
    fprintf(f, "w");
  }
  fprintf(f, "\n");
  for (int i = 0; i < 100; i++) {
    fprintf(f, "w");
  }
  fprintf(f, "\n");

  fclose(f);
  return EXIT_SUCCESS;
}
caution

the program will fail when one line is longer than UINT64_MAX. To avoid these i need either a bigger int type 128 bits or 256 bits for extended boundries OR check if we are already at maxvalue each step...

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

#define MAX 1000
#define UINT64_MAX 0xFFFFFFFFFFFFFFFF
// this actually works but the compiler will give a warning that the shifted
// value is one too much that is why i have chosen to use the hex presentation
//#define UINT64_MAX (1ULL << 64) -1

unsigned long int gl(char line[], int maxline);
void cp(char to[], char from[]);

int main() {
  unsigned long int max;
  unsigned long int len;
  char line[MAX];
  char longest[MAX];
  max = 0;
  while ((len = gl(line, MAX)) > 0) {
    if (len > max) {
      max = len;
      cp(longest, line);
    }
  }
  if (max > 0) {
    printf("%s", longest);
    if (max > 1000) {
      printf("...\n");
    }
    printf("longest line: %lu\n", max);
  }
  return EXIT_SUCCESS;
}

unsigned long int gl(char s[], int lim) {
  int c;
  int lastchar = 0;
  unsigned long int i;
  for (i = 0; (c = getchar()) != EOF && c != '\n'; i++) {
    if (i < lim - 1) {
      // save max lim chars
      // but count further and discard the rest
      s[i] = c;
      lastchar = i;
    }
  }
  if (c == '\n') {
    s[lastchar] = c;
    lastchar++;
  }
  s[lastchar] = '\0';
  return i;
}

void cp(char to[], char from[]) {
  int i;
  i = 0;
  while ((to[i] = from[i]) != '\n') {
    ++i;
  }
}