[c] C programming: Dereferencing pointer to incomplete type error

You are using the pointer newFile without allocating space for it.

struct stasher_file *newFile = malloc(sizeof(stasher_file));

Also you should put the struct name at the top. Where you specified stasher_file is to create an instance of that struct.

struct stasher_file {
    char name[32];
    int  size;
    int  start;
    int  popularity;
};