fscanf_s needs work

I'm trying to use fscanf_s and fgetc to read an OBJ file, but when I debug I get the error:
Unhandled exception at 0xfefefefe in Final Project.exe: 0xC0000005:
Access violation reading location 0xfefefefe.
I imagine this is a problem with my error handling for fscanf_s, but I feel I may be running into problems soon. I'm posting this in advance while I work on it to see if anyone gets a solution before me. Here's the relevant code.

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include "HeliParser.h"

#define BUFFER 100

namespace cole_parser{

void parse(){
FILE* fp = NULL;
try{
int except = fopen_s(&fp, "cube.obj", "r");
if(fp == NULL || except){
throw 0;
}
}
catch(int exception){
printf("program failed\n");
exit(exception);
}
char b[BUFFER]; // buffer

do{
fscanf_s(fp, "%s", b, BUFFER);
if(b[0] == '#'){// This line is commented; kill it.
#if DEBUG 1
printf("comment here\n");
#endif
kill_ln(fp);
}else if(b == "mtllib"){// This line names the material library; kill it for now.
kill_ln(fp);
}else if(b[0] == 'v'){// This line defines a vertex; store it.
}else if(b == "usemtl"){// This line names the material in use; kill it for now.
kill_ln(fp);
}else if(b[0] == 's'){// This line would set a smoothing group, but it's no longer in use; kill line.
kill_ln(fp);
}else if(b[0] == 'f'){// This line defines a face; store it.
}
}while(b[0] != EOF);

fclose(fp);
}

void kill_ln(FILE* fp){
char discard; // Character to check if end of file or end of line has been reached
do{
discard = fgetc(fp);
}while(discard != '\n' && discard != EOF);
}
}