File saving error [Error] cannot pass objects of non-trivially-copyable type 'std::string {aka class std::basic_string<char>}' through '...'

I'm pretty new in the coding world so i can't seem to understand this error. I'm creating a product management program wherein you enter product details and put that data on a file and then view it from the file via cmd but this error keeps popping up whenever I use fprintf or fputs.

my code:

#include<iostream>
#include<stdio.h>
#include<string.h>
using namespace std;

struct product{
    string Id,Name,Brand;
    int type, price, quan;
    product *next;
};
int main(){
    product *a,*b,*c,*d,*e,*f;
    a = new product;
    b = new product;
    c = new product;
    d = new product;
    e = new product;
    f = new product;
    FILE *productRecord;
    productRecord = fopen("Product Record","r");
    int choice;
    cout << "\nProduct Record\n1)Add Product\n2)Update Product Details\n3)Delete Product\n4)View Product By Brand or Type\n5)Exit\n\nEnter Choice: ";
    cin >> choice;
        if(choice == 1){
            char tempId[11],tempName[60],tempBrand[60];
            int temp_type, temp_price, temp_quan;
            productRecord = fopen("Product Record","a");
            cout << "Enter Product ID No.(Maximum of 10 Digits): ";
            cin >> tempId;
            a -> Id = tempId;
            a -> next = b;
            cout << "Enter Product Name(No Special Character): ";
            cin >> tempName;
            b -> Name = tempName;
            b -> next = c;
            cout << "Types:Canned(1),Frozen(2),Drinks(3),Produce(4),Meat/Seafood(5),Cleaning(6)\nEnter Product Type(1-6): ";
            cin >> temp_type;
            c -> type = temp_type;
            c -> next = d;
            cout << "Enter Product Brand(No spaces): ";
            cin >> tempBrand;
            d -> Brand = tempBrand;
            d -> next = e;
            cout << "Enter Product Price: ";
            cin >> temp_price;
            e -> price = temp_price;
            e -> next = f;
            cout << "Enter Product Quantity: ";     
            cin >> temp_quan;
            f -> quan = temp_quan;
            f -> next = NULL;

            fprintf(productRecord, "%s", a -> Id); //this is the error





            fclose(productRecord);
        }
        else if(choice == 2){
        }
        else if(choice == 3){
        }
        else if(choice == 4){
        }
        else if(choice == 5){
        }
    return 0;
}