Thread: Why does realloc cause a segfault here?

I'm looking at this code, but I can't seem to figure out why it's segfaulting.
The purpose of the function is to put each period separated word (token) into a list that grows as large as necessary.
[Edit: Oh, uh, this is C89.]

Code:

#include <stdlib.h>
static int getdots(char* input, char** keylist) {
	keylist = calloc(1, sizeof(char*));

	int i = 0;
	keylist[i] = malloc(512* sizeof (char));
	memset(keylist[i],'\0', 512*sizeof(char));
	char* p = input, *c=keylist[0];
	while (*p!='\0') {

		while(c && p)
		if(*p!='.')
		*c++=*p++;
		else
		break;

		if(*p=='.')
		{

			i++;
			keylist=realloc(keylist, sizeof(char*)*(i+1));
			keylist[i]=malloc(512*sizeof(char));
			c=keylist[i];
			memset(keylist[i],'\0', 512*sizeof(char));
		}
		p++;
	}
	return 0;
}

int main() {

	char input[512] = { "hello.helm.happy\0" };
	char** keylist = NULL;
	getdots((char*) &input, keylist);
	if (!keylist) {
		printf("Nothing happened!\r\n");
		return 0;
	}
	int i = 0;
	for (i = 0; keylist[i]; i++)
		printf("%s\r\n", keylist[i]);
	if (keylist != NULL)
		free(keylist);
	return 0;

}

Code:

while(c && p)

The chances of these actually pointing to NULL are very slim. You should be checking to see that you don't run past your line length, or that they contain '\0'. A pointer pointing at a character containing '\0' will pass a NULL check.

Code:

#include<stdio.h>
int main( void )
{
    char c = '\0';
    char *p = &c;

    if( p )
    {
        printf( "Not null.\n" );
    }

    return 0;
}

Quzah.

It's now working.
For whatever it's worth, here is the fixed program:

Code:

#include <stdlib.h>
#include <ctype.h>
#include <stdio.h>
#include <string.h>
#define LOWER(c)   (((c)>='A'  && (c) <= 'Z') ? ((c)+('a'-'A')) : (c))
static char** getdots(char* input, char** keylist) {

	int i=0;
	keylist[i]=malloc(512*sizeof(char));
	memset(keylist[i],'\0', 512*sizeof(char));
	char* p = input, *c=keylist[i];
	while (*p!='\0') {

		while(*p!='.' && *p!='\0')
		*c++=*p++;

		if(*p=='\0')
		{
		
		return keylist;
		}
		if(*p=='.')
		{
		i++;
		keylist= realloc(keylist, sizeof(char*)*(i+1));
		if(!keylist){
		printf("Keylist broken.\r\n");
		return NULL;
		}
		keylist[i]=malloc(512*sizeof(char));
		c=keylist[i];
		memset(keylist[i],'\0', 512*sizeof(char));
		}
		p++;
	}
	return keylist;
}

int isname(const char *str, const char *namelist) {
	const char *curname, *curstr;
	curname = namelist;
	for (;;) {
		for (curstr = str;; curstr++, curname++) {
			if (!*curstr && !isalpha(*curname))
				return (1);

			if (!*curname)
				return (0);

			if (!*curstr || *curname == ' ' || *curname == '-' || *curname == ',')
				break;

			if (LOWER(*curstr) != LOWER(*curname))
				break;
		}

		/* skip to next name */

		for (;isalpha(*curname); curname++)
			;
		if (!*curname)
			return (0);
		curname++; /* first char of new name */
	}
}


int main()
{

char input[512]={"big.r.helm.yay\0"};
char sdesc[512]={"a big, red helm\0"};
char** keylist=NULL;
keylist=calloc(1,sizeof(char*));

keylist=getdots((char*) &input, keylist);
if(!keylist)
{
printf("Nothing happened!\r\n");
return 0;
}
int i=0;
for(i=0;keylist[i];i++)
{
printf("%s\r\n",keylist[i]);
if(isname(keylist[i], sdesc))
printf("%s is in the list.\r\n", keylist[i]);
else
printf("%s is not in the list.\r\n", keylist[i]);
}

if(keylist)
free(keylist);

return 0;




}

Indentation needs work, and there's still a couple of bugs....