Hackerrank: C - Querying the Document - c

Question

I'm stuck with an unidentified Segmentation Fault.
My erroneous function receives a string text. It should convert it into a document and return it. A document is made of paragraphs(separated by '\n') which is made of sentences(separated by '.') which is made of words(separated by ' '). You may refer the complete problem statement here.
Here is the relevant part of my code:
char**** get_document(char* text) {
int p = 0, s = 0, w = 0, c = 0;
char**** document;
document = malloc(sizeof(char***));
document[0] = malloc(sizeof(char**));
document[0][0] = malloc(sizeof(char*));
document[0][0][0] = malloc(sizeof(char));
while (*text)
{
if (*text == ' ')
{
c = 0;
++w;
document[p][s] = realloc(document[p][s], sizeof(char*) * (w + 1));
}
else if (*text == '.')
{
c = 0;
w = 0;
++s;
document[p] = realloc(document[p], sizeof(char**) * (s + 1));
}
else if (*text == '\n')
{
c = 0;
w = 0;
s = 0;
++p;
document = realloc(document, sizeof(char***) * (p + 1));
}
else
{
++c;
document[p][s][w] = realloc(document[p][s][w], sizeof(char) * (c + 1));
document[p][s][w][c - 1] = *text;
document[p][s][w][c] = '\0';
}
++text;
}
return document;
}
After debugging, I came to know that the program crashes when
w = 1 at document[p][s][w][c - 1] = *text;
I have no idea why this is happening. I checked the values of p, s, w, and c before the execution of that statement, and if the realloc statements were executing properly.
But in vain!
What might be going wrong in my code?

Answer 1

You need to allocate memory for the new paragraphs, sentences and words. By reallocation you increased the actual dimension size, but the new element was a null pointer which caused the segfault.
char**** get_document(char* text) {
int p = 0, s = 0, w = 0, c = 0;
char**** document;
document = malloc(sizeof(char***));
document[0] = malloc(sizeof(char**));
document[0][0] = malloc(sizeof(char*));
document[0][0][0] = malloc(sizeof(char));
while (*text)
{
if (*text == ' ')
{
c = 0;
++w;
document[p][s] = realloc(document[p][s], sizeof(char**) * (w + 1));
document[p][s][w] = malloc(sizeof(char*));
}
else if (*text == '.')
{
c = 0;
w = 0;
++s;
document[p] = realloc(document[p], sizeof(char**) * (s + 1));
document[p][s] = malloc(sizeof(char**));
document[p][s][w] = malloc(sizeof(char*));
}
else if (*text == '\n')
{
c = 0;
w = 0;
s = 0;
++p;
document = realloc(document, sizeof(char****) * (p + 1));
document[p] = malloc(sizeof(char***));
document[p][s] = malloc(sizeof(char**));
document[p][s][w] = malloc(sizeof(char*));
}
else
{
++c;
document[p][s][w] = realloc(document[p][s][w], sizeof(char) * (c + 1));
document[p][s][w][c - 1] = *text;
document[p][s][w][c] = '\0';
}
++text;
}
return document;
}
Moreover, your printing method in the main does not work, because you did not save the spaces (you needn't anyways). So, I fixed it:
int main()
{
char* text = "New word.No space before a sentence.\nThis is a new paragraph.";
char**** doc = get_document(text);
int p = 0, s = 0, w = 0, c = 0;
char ch;
while (ch = *text)
{
if (ch == ' ')
{
putchar(' ');
c = 0;
++w;
}
else if (ch == '.')
{
putchar('.');
c = 0;
w = 0;
++s;
}
else if (ch == '\n')
{
putchar('\n');
c = 0;
w = 0;
s = 0;
++p;
}
else putchar(doc[p][s][w][c++]);;
text++;
}
return 0;
}
The output seems correct:
New word.No space before a sentence.
This is a new paragraph.
I think you don't have to free the doc because you are returning from the main after it and Hackerrank will handle that if needed. But just note that you should take care of it otherwise.