bad ptr on fopen in visual studio C

Here's a program in C that I've been working on. The important parts are highlighted.
I've tried both fopen, and fopen_s, and they both give me <bad ptr> when I debug. Can anyone help?

void main(){
struct node** primes; //linked list of all primes found so far
int current; //value currently being checked for prime

FILE* fp = NULL;
fp = fopen("primes.txt", "r+");
primes = NULL;
current = 3;

if(fp == NULL){
printf("No saved progress found.\nTime to kick *** and take primes.\n");
fp = fopen("primes.txt", "w+");
primes = addVal(&fp, 2, primes);
}
else{
printf("Saved progress found.\nLoading file to continue previous progress.\n");
initList(&fp, primes);
}

while(1){
primes = check(&fp, current, primes);
current += 2;
}

fclose(fp);
return;
}

 

Ok, nevermind. C is stupid, but apparently <Bad Ptr> can mean it works fine. It's just that when you first open a file, some things haven't been initialized.