Question

I am doing a homework assignment that reads in a book. First, a line is read in and a pointer made to point at that line. Then a paragraph function reads in lines and stores their address into a array of pointers. Now, I am on reading a chapter (a paragraph recognized by the next line being broke). It should call get_paragraph() and store the address of paragraphs until it comes to a new chapter.

A new chapter is the only time in the book where the first character in the line is not a space. I think this is were I am having problems in my code. All functions up to this point work. I hope I have provided enough information. The code compiles but core dumps when started.

I am a student and learning so please be kind. Thanks.

char*** get_chapter(FILE * infile){

    int i=0;

    char **chapter[10000];//an array of pointers 
    // Populate the array
    while(chapter[i]=get_paragraph(infile)) { //get address store into array
      if(!isspace(**chapter[0])){    //check to see if it is a new chapter<---problem line?
        // save paragraph not used in chapter using static to put into next chapter
        break;
      }
      i++;//increment array
    }
    //add the null
    chapter[++i]='\0';//put a null at the end to signify end of array
    //Malloc the pointer
    char**(*chap) = malloc(i * sizeof(*chap));//malloc space
    //Copy the array to the pointer
    i=0;//reset address
    while(chapter[i]){//while there are addresses in chapter
      chap[i] = chapter[i++];//change addresses into chap
    }
    chap[i]='\0';//null to signify end of chapter
    //Return the pointer
    return(chap);//return pointer to array
  }

For those who would rather see without comments:

 char*** get_chapter(FILE * infile){

    int i=0;

    char **chapter[10000];
    while(chapter[i]=get_paragraph(infile)) { 
      if(!isspace(**chapter[0])){   
        break;
      }
      i++;
    }
    chapter[++i]='\0';
    char**(*chap) = malloc(i * sizeof(*chap));//malloc space
    i=0;
    while(chapter[i]){
      chap[i] = chapter[i++];
    }
    chap[i]='\0';
    return(chap);
  }

Answer 1

Can I suggest that you use for loops instead of whiles? You need to stop if you run out of space, so you might as well use the appropriate construct.

I suspect you have a bug in this code:

while(chapter[i]=get_paragraph(infile)) { 
  if(!isspace(**chapter[0])){   
    break;
  }
  i++;
}
chapter[++i]='\0';

Firstly, shouldn’t it be chapter[i] instead of chapter[0]? You want to know if the pointer at chapter[i] points to a space, not the first pointer in chapter. So this will probably loop indefinitely – hence the need for a for loop, so you don’t just loop forever accidentally.

Secondly, you increment i at the end of the while block, and then again in the chapter[++i] assignment. i has already been incremented by the final loop execution before the while condition breaks, so it is already the correct position to use. ++i increments before yielding the value, so presumably you meant to have i++ here, so that it would increment after yielding the current value of i. Either way, it’s confusing one of us as to what you mean, so maybe just put the increment on a separate line for clarity. The compiler will sort out any available optimisation.

Finally (and I might well be wrong here) why are you setting the value to '\0'? That’s a null character, isn’t it? But your array is of pointers. The null pointer would be 0, rather than '\0', I think. If I’m right, you might have still got away with it if '\0' yields the same set of zeroes as the null pointer.