// pic_links is a private vector of the class generate_post
void generate_post::delete_used_pics(char* file) {
 
	int match=0;
	ofstream outfile;
 
	outfile.open(file);
 
	if (!outfile) {
		cout << "Failed to open file";
	}
	for (int i=0; i<(int)pic_links.size(); i++) {
		for (int j=0; j<6; j++) {
			if (pic_links.at(i) == post[j]) {
				match++;
		pic_links.erase(pic_links.at(i)); // the error occurs here
			}
		}
		if (match==0) {
			outfile << "http://inspic.com" << pic_links.at(i) << "\n";
		}
		match=0;
	}
 
	outfile.close();
}

pic_links.erase(pic_links.begin()+i);