C Programming Read File Line by Line Into Array

1. C: read File into Array

   Hello,

   I am attempting to read a file into an array on C:

   Code:

   #include <stdio.h> #include <stdlib.h>  /*How to read a file into an array*/ int chief() {  double array[29999];  double fourth dimension;  FILE *fp;  unsigned int i = 0;  fp = fopen("alpha2.99","r");  if (fp != Aught) {     while (!feof(fp)) {        fscanf(fp,"%lf %lf",&time,&assortment[i]);        printf("%lf\northward",assortment[i]);        i++;     }  }  fclose(fp);  render 0; }

   The file looks similar:
   

   Code:

   0.0 45.344 0.ane 47.464 ... 2999.9 224.879 3000.0 245.080

   I am simply press the 2nd column right now (nice and like shooting fish in a barrel at first, of form). However, information technology always prints an extra 0 when I exercise this in real life:

   Lawmaking:

   244.555000 245.338000 224.879000 245.080000 0.000000

   The immediately obvious answer seemed to exist to reduce the size of the array. Reducing the size of the array, however, leads to:

   Lawmaking:

   244.555000 245.338000 224.879000 Segmentation fault (core dumped)

   Is there a mode I can remove that abaft nil?

   Thanks for your expertise!

   ---

2. Re: C: read File into Array

   Use of feof() tin can be a chip tricky at first. Here's what happens in your instance: the get-go lines are read unremarkably. When the concluding line is read, the end-of-file indicator is Non fix. This is considering your program just reads until the last newline grapheme. It does not "look" after it, and so it does not know that there is nada and that the line is in fact the last line of the file. Thus later on it has read the last line, it enters the loop one more than time, and this is where it sees that at that place is nothing more than to read, and sets the end-of-file indicator.

   One possible solution would be to check with the return falue of fscanf(). Something like

   Lawmaking:

                         while (!feof(fp)) {        if (fscanf(fp,"%lf %lf",&time,&array[i]) != 2) {          go along;        }        printf("%lf\n",array[i]);        i++;     }

   This as well allows to silently ignore invalid lines.

   Concluding edited past Bachstelze; July 15th, 2012 at 10:30 PM. Reason: Posted lawmaking

   ---

3. Re: C: read File into Array

   Originally Posted past Bachstelze

   Use of feof() can be a bit catchy at get-go. Here'due south what happens in your case: the first lines are read normally. When the terminal line is read, the end-of-file indicator is NOT set. This is because your program just reads until the last newline graphic symbol. It does not "look" afterwards it, so it does not know that there is nil and that the line is in fact the last line of the file. Thus after it has read the final line, it enters the loop i more fourth dimension, and this is where it sees that there is zilch more to read, and sets the stop-of-file indicator.

   I possible solution would be to check with the return falue of fscanf(). Something like

   Code:

                             while (!feof(fp)) {        if (fscanf(fp,"%lf %lf",&time,&array[i]) != ii) {          continue;        }        printf("%lf\due north",array[i]);        i++;     }

   This also allows to silently ignore invalid lines.

   Hi Bachstelze,

   thank you for your reply! It works!

   And then fscanf only works if it does not return a value of two? I tried writing a program to return the value of fscanf, but it didn't work:

   Code:

   #include <stdio.h> #include <stdlib.h>  int main() {  FILE *fp;  fp = fopen("alpha2.99","r");  int i, time, tor;  while (!feof(fp)) {     i = fscanf("%lf %lf",&fourth dimension, &tor);  }  fclose(fp);  printf("%d\n",i);  return 0; }

   ---

4. Re: C: read File into Array

   Originally Posted by hailholyghost

   Then fscanf only works if information technology does not return a value of two?

   No. Check the manual page to run into how the return value of fscanf() is adamant.Scroll down to the "Return value" section. If you don't have the man page, install manpages-dev.

   ---

5. Re: C: read File into Assortment

   Cheers so much! I wish I were able to help yous out Bachstelze, lol. If only I could.

   The return value is the number of arguments co-ordinate to the man page.

   Merci!

   ---

6. Re: C: read File into Array

   Originally Posted by hailholyghost

   The return value is the number of arguments co-ordinate to the man page.

   No, it is non.

   RETURN VALUE
   These functions render the number of input items successfully matched and assigned, which can be fewer than provided for, or even cipher in the outcome of an early matching failure.

   If information technology were, and then it would ever return the aforementioned value in your lawmaking, so checking for it would be useless.

   ---

johnsonalittly.blogspot.com

Source: https://ubuntuforums.org/showthread.php?t=2026618

Share this post