Read from a Text File - Segmentation Fault

Hello All,

This post is regarding reading from a text file.

Background - I am trying to fill my Text struct field member char** lines with the strings from text file. However, I am having trouble simply reading from the text file itself.

I am thinking that there is an error with my while loop but am having some difficulty debugging. Anyone have an idea why my while loop is triggering a Segmentation Fault?

My code is here:

Code:

---

bool fill_text(Text* text, char* fileName)
{
      FILE *filePtr = fopen(fileName, "r");
     
      if(filePtr == NULL)
      {
            return false;
      } else {

            char** line = text->lines;
            int max = text->maxLineCount;
            int iter = 0;

            while (fgets(line[iter], max, filePtr) != NULL)
            {
                  // Printing line[iter] here to see if fgets and while are working correctly.
                  printf("%s\n",line[iter]);
                  iter++;
            }

            return true;
      }

}

---

Just in case, allow me to ask the obvious question: did you allocate sufficient storage for the strings? I notice that you have max line count, but that sounds like the maximum number of lines rather than the maximum number of characters (including null character) per line, which is what fgets requires. You should be comparing iter with max instead to avoid exceeding the max number of lines.

aah, good point! I was not certain I had to allocate storage for the strings. (I am a bit new to pointers and memory allocation in C). The trick with this problem is that the size of the text file to be read from is unknown - meaning the number of lines, characters, and number of strings is unknown as well. Perhaps I could allocate a large amount of memory before hand?

Your understanding about what max line represents is correct.

I thought that fgets would read from the text file until the EOF character was encountered - or is that assumption incorrect?

It depends when fgets stops.
Let's say you want to read 80 characters. If the file is less than 80 charaters long, fgets will stop when reaching the end.
If fgets reads an '\n' before 80 characters are read it will stop too, otherwise it will stop after 80 characters.