if (p = NULL)
should be
if (p == NULL)
in strdup
Question
This is for a class assignment. I just need to read words from an input file into tree nodes, and catalog them by frequency. Unfortunately, I'm getting a segfault. I've run the program through gdb, and I've found that the fault occurs during the second pass through addtree. It hits strcmp(w, p->word)
and faults.
Upon further investigation, it looks like this is because p->word
has a value of 0x0
, as if the string never got copied into it. Is there something really simple that I'm missing? I'll try to include only the offending and related bits of code here. (edit: looks like that was everything except treeprint
.)
#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <stdlib.h>
#define MAXWORD 100
struct tnode *addtree(struct tnode *, char *);
void treeprint(struct tnode *);
int getword(char *, int);
char *strdup(const char *);
struct tnode
{
char *word;
int count;
struct tnode *left;
struct tnode *right;
};
main()
{
struct tnode *root;
char word[MAXWORD];
root = NULL;
while (getword(word, MAXWORD) != EOF) {
if (isalpha(word[0])) {
root = addtree(root, word);
}
}
treeprint(root);
return 0;
}
int getword(char *word, int lim)
{
char *w = word;
int c;
while (isspace(c = getch())) {}
if (c != EOF)
{
*w++ = c;
}
if (!isalpha(c))
{
*w = '\0';
return c;
}
for ( ; --lim > 0; w++)
{
if (!isalnum(*w = getch()))
{
ungetch(*w);
break;
}
}
*w = '\0';
return word[0];
}
struct tnode *talloc(void)
{
return (struct tnode *) malloc(sizeof(struct tnode));
}
char *strdup(const char *s)
{
char *p;
p = (char *) malloc(strlen(s) + 1);
if (p == NULL)
strcpy(p, s);
return p;
}
struct tnode *addtree(struct tnode *p, char *w)
{
int cond;
if (p == NULL)
{
p = talloc();
p->word = strdup(w);
p->count = 1;
p->left = p->right = NULL;
}
else if ((cond = strcmp(w, p->word)) == 0)
p->count++;
else if (cond < 0)
p->left = addtree(p->left, w);
else
p->right = addtree(p->right, w);
return p;
}
void treeprint(struct tnode *p)
{
if (p != NULL)
{
treeprint(p->left);
printf("%4d %s\n", p->count, p->word);
treeprint(p->right);
}
}
La solution
if (p = NULL)
should be
if (p == NULL)
in strdup