Read in multiple integer arrays from one file

Question

I have a problem where I need to read in multiple arrays from a .txt file and output the maximum sum subarray. Here is the text file:

[1, 4, -9, 8, 1, 3, 3, 1, -         


        

Answer 1

Divide and conquer. Break task into pieces. Putting each piece into a separate function helps.

unable to figure out how to read the integers in and place them in separate arrays

Only 2 int arrays needed: The current array of int read and the best one. Use read_ints() to read one line. Various tests were applied to insure data was as expected. A classic approach is to read a line into a buffer (might need 100*40 char for a worst case) and then process it. The below reads pieces of a line, look for the start-of-Frame '[' and end-of-frame ']' to insure data integrity.

#include <ctype.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>


#define StartOfFrame '['
#define Separator ','
#define EndOfFrame ']'
#define INT_COUNT_MAX 100

// Return number of `int` read
// or 0 on syntax error
// or EOF
int read_ints(int *dest, int size, FILE *inf) {
  int ch;
  char delimiter = 0;
  ch = fgetc(inf);
  if (ch == EOF) return EOF;
  if (ch != StartOfFrame) return 0; // unexpected text
  int i;
  for (i = 0; i < size; i++) {
    if (fscanf(inf, "%d%c", &dest[i], &delimiter) != 2) return 0;
    if (delimiter == EndOfFrame) break;
    if (delimiter != Separator) return 0;
  }
  do {
    ch = fgetc(inf);
    if (ch == '\n' || ch == EOF) return i;
  } while (isspace(ch));
  return 0; // unexpected text
}

OP's offered double maxSubArray(double * Array1);, but that lacks a length of valid int. Of course that array could be pre-filled with 0.

In writing a complete solution, the various error checking helped in quickly identifying problems.

The below read_lines() wraps the repeated calls of read_ints() and processes the results.

OP Ignore the rest should you not want to see the complete solution.

int read_lines(FILE *inf) {
  int best[INT_COUNT_MAX];
  unsigned best_line = 0;
  int best_count = 0;
  long long best_sum = LLONG_MIN;
  int a[INT_COUNT_MAX];
  unsigned line_count = 0;

  int count;
  while ((count = read_ints(a, INT_COUNT_MAX, inf)) >= 0) {
    line_count++;
    if (count == 0) {
      fprintf(stderr, "Trouble reading line %u\n", line_count);
      return 1;
    }
    long long sum = 0;
    for (int i = 0; i < count; i++) {
      sum += a[i];
    }
    if (sum > best_sum) {
      best_sum = sum;
      best_count = count;
      best_line =line_count;
      memcpy(best, a, sizeof best[0] * count);
    }
  }
  printf("Greatest sum:%lld on line:%u\n", best_sum, best_line);
  fputc(StartOfFrame, stdout);
  for (int i = 0; i < best_count; i++) {
    if (i > 0) printf("%c", Separator);
    printf("%d", best[i]);
  }
  fputc(EndOfFrame, stdout);
  return 0;
}
int main(void) {
  const char *filename = "MSS_TestProblems.txt";
  FILE *myFile;
  myFile = fopen(filename, "r");
  if (!myFile) {
    fprintf(stderr, "Unable to open file \"%s\"\n", filename);
    return 1;
  }
  read_lines(myFile);
  fclose(myFile);
  return 0;
}

--

Greatest sum:81 on line:6
[12,99,99,-99,-27,0,0,0,-3]

Answer 2

Read in the file with fread calls into a buffer. Explode buffer per line (\n) / array. (Count how many arrays do you need and prepare.) Explode lines per numbers - separator: comma and space. (Count length of array and allocate.) Numbers would contain sign and digits. Assuming digits are contiguous in range '0'..'9', '0'+digit gives the value of the digit. Value of the number can be calculated from sign, digit values and their order.