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:

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#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;

}

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Code:

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while(c && p)

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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:

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

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

    return 0;
}

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Quzah.

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

Code:

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#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;




}

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