Strtok on text file leads to seg fault

I have a text file that reads as follows:

5f6
2c6
4g6

I'd like to obtain the numbers from that textfile (as chars then convert them to integers using strtol()

I have the code:

char *ptr;
char *ptr2;
char *ptr3;
char *ptr4; //redundant but attempting these before I'm doing `char * []`
char buf[100];

while (fgets(buf,100,file) )

ptr = strtok(buf,"f");
ptr2 = strtok(NULL," ");
ptr3 = strtok(NULL, "f");
ptr4 = strtok(NULL, " ");

however, the program seg faults but compiles. How would I go about doing this more efficiently (By a method that doesn't seg fault)?