CODEWITHSUNDEEP
cloopsfile-io
BradStevenson
BradStevenson

Reputation: 1994

handling trailing \n when using feof()

I have written a small program which takes input of a file such as:

13,22,13,14,31,22, 3, 1,12,10
11, 4,23, 7, 5, 1, 9,33,11,10
40,19,17,23, 2,43,35,21, 4,34
30,25,16,12,11, 9,87,45, 3, 1
1,2,3,4,5,6,7,8,9,10

and outputs the largest sum of numbers on each line that is less than 50.

However if the inputted file has a trailing newline character the loop runs one too many times and hence another line is added to the array with random data. So I'm looking for a better way to do this comparison to avoid this issue. I'm also assuming all lines have 10 integers on at the moment as i cannot think of a better way to do the end of line loop comparison.

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

void readLineData(int lineNo, int val[][10], FILE *fp);
int findSum(int lineNo, int val[][10], FILE *fp);

int main(int argc, char *argv[]) {
  FILE *fp;
  int val[5][10];

  // Open file.
  if ((fp = fopen(argv[1], "r")) == NULL)
    {
    perror("Cannot open file ");
    exit(EXIT_FAILURE);
    }


  for (int i = 0; !feof(fp); i++) // runs too many times if file ends with '\n'
    {
      readLineData(i, val, fp);
      printf("%d\n", findSum(i, val, fp));
    }

 fclose(fp);
 return EXIT_SUCCESS;
}

void readLineData(int lineNo, int val[][10], FILE *fp) {
  char c;  
  for (int i = 0; i < 10; i++) // assuming line contains 10 integers
    {
      fscanf(fp, "%d,", &val[lineNo][i]);
    }
}

int findSum(int lineNo, int val[][10], FILE *fp) {
  int highVal = 0;
  int value1 = 0;
  int value2 = 0;

  for(int i = 0; i < 10; i++) //each letter
    {
      for(int j = 0; j < 10; j++)// every other letter
    {
      if((val[lineNo][i] + val[lineNo][j]) > highVal && i != j && (val[lineNo][i] + val[lineNo][j]) <= 50)
        {
          highVal = val[lineNo][i] + val[lineNo][j];
          value1 = val[lineNo][i];
          value2 = val[lineNo][j];
        }
    }
    }
  printf("Line %d: largest pair is %d and %d, with a total of: ", lineNo+1, value1, value2);
  return highVal;
}

any help with those loop comparisons and general notation tips is most welcome.

Thanks

Upvotes: 0

Views: 114

Answers (3)

hmjd
hmjd

Reputation: 122011

The posted code does not distinguish between two lines that have five integers and (the expected) one line that has 10 integers. Suggest reading in a line at a time, using fgets() and then using sscanf() on the read line to ensure that all the read integers belong to the same line.

Check the return value of input operations. For example, sscanf() (and fscanf()) return the number of assignments made. Only process lines that have the expected 10 integers, which would detect invalid lines including the trailing empty line.

For example:

/* Returns 1 on success and 0 on failure. */
int readLineData(int lineNo, int val[][10], FILE *fp)
{
    char line[1024]; /* Arbitrarily large. */
    if (fgets(line, sizeof(line), fp))
    {
        /* %n records position where processing ended. */
        int pos;
        const int result = sscanf(line,
                                  "%d,%d,%d,%d,%d,%d,%d,%d,%d,%d%n",
                                  &val[lineNo][0],
                                  &val[lineNo][1],
                                  &val[lineNo][2],
                                  &val[lineNo][3],
                                  &val[lineNo][4],
                                  &val[lineNo][5],
                                  &val[lineNo][6],
                                  &val[lineNo][7],
                                  &val[lineNo][8],
                                  &val[lineNo][9],
                                  &pos);

        /* 10 integers and full line processed,
           except if new-line character present. */
        return 10 == result &&
               (pos == strlen(line) ||
                (pos + 1 == strlen(line) && '\n' == line[pos]));
    }
    return 0;
}

Upvotes: 2

iabdalkader
iabdalkader

Reputation: 17342

you could check if fscanf fails in your readLineData function:

int readLineData(int lineNo, int val[][10], FILE *fp) {
  for (int i = 0; i < 10; i++) {// assuming line contains 10 integers
     if (fscanf(fp, "%d,", &val[lineNo][i]) != 1) {
         return 1;
     }
  }
  return 0;
}

Upvotes: 0

Chris Hayes
Chris Hayes

Reputation: 12050

You could simply consume the newline character yourself:

for (int i = 0; !feof(fp); i++) // runs too many times if file ends with '\n'
{
  readLineData(i, val, fp);
  printf("%d\n", findSum(i, val, fp));
  fscanf(fp, "%*c"); // read a character without storing it in a variable
}

Note that there are undoubtedly better ways that involve reading an entire line at once and simply examining its contents; but this is the easiest way that will fit with what you already have.

Upvotes: 0

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