Thread: help with segmentation fault, binary tree

I have tried several solutions from other sites, but none of them worked. It always gives this "segmentation fault" message. please tell me what's wrong. thanks in advance!

Code:

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

struct tnode {
	char *word;
	int count;
	struct tnode *left;
	struct tnode *right;
};

struct tnode *addtree ( struct tnode *p, char *w );
struct tnode *talloc ( void );
int strcmp ( char *t, char *s );
void cpword ( char *from, char *to );
void treeprint ( struct tnode *p );
char getword ( char *word );

int main ( void )
{
	char word [20];
	struct tnode *root;

	printf ( "enter the text below:\n\n" );
	while ( ( getword ( word ) ) != EOF )
		if ( isalpha ( word ) )
			addtree ( root, word );

	printf ( "\n%-20s: %s\n\n", "word", "count" );
	treeprint ( root );
	return 0;
}

struct tnode *addtree ( struct tnode *p, char *w )
{
	int temp;

	if ( p == NULL ) {
		p = talloc ();	
		cpword ( w, p->word );
		p->left = NULL;
		p->right = NULL;
		p->count = 0;
	}
	else if ( ( temp = strcmp ( w, p->word ) ) == 0 )
		++p->count;
	else if ( temp < 0 )
		p->left = addtree ( p->left, w );
	else
		p->right = addtree ( p->right, w );

	return p;
}

struct tnode *talloc ( void )
{
	return ( ( struct tnode * ) malloc ( sizeof ( struct tnode ) ) );
}

int strcmp ( char *t, char *s )
{
	while ( *t && *s ) {
		if ( *t == *s ) {
			t++;
			s++;
		}
		else
			return ( *t - *s );
	}
	return 0;
}

void cpword ( char *from, char *to )
{
	while ( *from )
		*( to++ ) = *( from++ );
	*to = '\0';
}

void treeprint ( struct tnode *p )
{
	if ( p != NULL ) {
		treeprint ( p->left );
		printf ( "%-20s: %d\n", p->word, p->count );
		treeprint ( p->right );
	}
}

char getword ( char *word )
{
	char temp;
	char *w = word;

	while ( !isalnum ( temp = getchar () ) )
		;
	while ( isalnum ( temp ) ) {
		*w++ = temp;
		temp = getchar ();
	}
	*w = '\0';

	return *word;
}

Do you have your compiler's warnings turned on? This shouldn't go by unnoticed:

Code:

if ( isalpha ( word ) )

isalpha() expects an int, not a char *.

addtree() returns a root, which you're ignoring.

Your root is also uninitialised.

Salem that’s actually good catch.

@OP - Could tell us where exactly does the SEG FAULT occurs. For me tho, the problem really start from on how you read a string and there is no break point to it. And its just keep going.

In addition could take the Salems advice on handling root pointer carefully. You will have initialised the pointer before you send them into the addtree function. As the pointer should pointer to random segment in the memory but not NULL. Which would eventually skip you if condition in the addtree function.

And also the way you store the read char into the array word ( or 'w' in your case is very dangerous). Doing this

Code:

*w++

Could lead into pointer moving beyond the boundary. Is there specific reason on not using function like fgets to read string of the user?

ssharish