C-如何（通过基于用户的输入）将各种字符串存储在结构内部的数组中？

Question

I'm relatively new to programming. I'm trying display all the data found in a previous user-based created file (user has to enter product code, product name and product price in a single entry). My code has a menu with 3 options:

1. Show all the data from the file (working only with the last entry from the option 2. Actually, I made the program to work intentionally like that, because I can't figure out how to print ALL the data in the file)
2. Add data to that file (working 100%)
3. Exit (working 100%)

PS: When I try to use the option (1) after re-opening the program, it displays just garbage. Is there a way to solve this problem? PS2: Sorry about my bad usage of the english language, I'm not native.

Here I display the whole code:

#include <stdio.h>
#include <stdlib.h>
#include <windows.h>

typedef struct
{

  unsigned long long codigo_producto;
  char nombre_producto[60];
  float precio_producto;

} datos_de_productos;

int i;

main()
{

  datos_de_productos datos;

  char U = 233;
  char o = 162;
  int x = 0;
  int tam;
  FILE *p_datos;

  p_datos = fopen("datos.txt", "a");
  fseek(p_datos, 0, SEEK_END);
  tam = ftell(p_datos);
  if (tam == 0)
  {
    p_datos = fopen("datos.txt", "w");
    fprintf(p_datos,
        "CODIGO DE PRODUCTO\tNOMBRE DE PRODUCTO\tPRECIO DE PRODUCTO\n\n\n");
    fclose(p_datos);
  }

  while (x != 3)
  {

    system("cls");
    system("color 84");
    printf("****** MEN%c PRINCIPAL ******\n\n", U);
    printf("(1) - Ver el %cltimo producto ingresado en esta sesi%cn\n", U, o);
    puts("(2) - Agregar datos");
    puts("(3) - SALIR\n");
    menu_principal: printf("Por favor, ingrese la opci%cn deseada: ", o);
    scanf("%i", &x);

    switch (x)
    {

    case 1:

      system("cls");
      system("color 84");
      p_datos = fopen("datos.txt", "r");
      if (fopen == NULL )
      {
        exit(1);
      }
      if (fopen != NULL )
      {
        printf(
            "CODIGO DE PRODUCTO\tNOMBRE DE PRODUCTO\tPRECIO DE PRODUCTO\n\n\n");
        fscanf(p_datos, "%llu %s %f", &datos.codigo_producto,
            datos.nombre_producto, &datos.precio_producto);
        printf("%llu\t\t%s\t\t%.2f\n", datos.codigo_producto,
            datos.nombre_producto, datos.precio_producto);
        fclose(p_datos);
        puts("\n\n");
        system("pause");
        system("color 0E");
      }

      break;

    case 2:

      system("cls");
      puts("Se ingresaran los datos con el siguiente prototipo:\n");
      puts("codigo_producto | nombre_producto | precio_producto\n");
      puts("Ejemplo: '1763482 Placa_de_video 749.99'\n");
      printf(
          "(n%ctese que se usan guiones bajos para separar las palabras)\n\n",
          o);
      system("pause");
      system("cls");
      system("color 0E");
      puts("codigo_producto | nombre_producto | precio_producto\n");
      scanf("%llu %s %f", &datos.codigo_producto, datos.nombre_producto,
          &datos.precio_producto);
      p_datos = fopen("datos.txt", "a");
      if (fopen == NULL )
      {
        exit(1);
      }
      if (fopen != NULL )
      {
        fprintf(p_datos, "%llu\t\t%s\t\t%.2f\n", datos.codigo_producto,
            datos.nombre_producto, datos.precio_producto);
        fclose(p_datos);
        system("color 84");
        puts("\nProducto cargado correctamente.");
        system("pause");
      }

      break;

    case 3:

      system("cls");
      system("color 0F");
      puts("Nos\t\t\t\t\t\t\t\tby viciecal");
      sleep(1);
      puts("Re");
      sleep(1);
      puts("Vimos");
      sleep(1);
      puts("\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\t\t\t\t\t\t\t\t\tputo");

      break;

    default:

      goto menu_principal;

      break;

    }
  }
}

Answer 1

The first line of your file will be what's inside this fprintf :

fprintf(p_datos,
        "CODIGO DE PRODUCTO\tNOMBRE DE PRODUCTO\tPRECIO DE PRODUCTO\n\n\n");

When you get to this line inside case 1 , the file will be opened at its start (first line):

p_datos = fopen("datos.txt", "r");

so this fscanf :

fscanf(p_datos, "%llu %s %f", &datos.codigo_producto,
            datos.nombre_producto, &datos.precio_producto);

will try to read a llu from this first line:

CODIGO DE PRODUCTO  NOMBRE DE PRODUCTO  PRECIO DE PRODUCTO

but will fail immediately because it won't find the llu , so you won't scan anything from the file (try to check the return value of fscanf and you'll see it will be 0 ).

---

Why do you see garbage getting printed?

Because, as I said, fscanf failed, so your program will print whatever garbage values were inside your struct, seeing that you haven't initialized it at the beginning of your code.

Try to initialize your struct's members to zero and you'll see the program printing zeroes.

---

So... trying to salvage the majority of your code and your logic, one workaround I can think of would be to create a char array called last_product for example and fgets from the file until it's end, so the last entry read into the buffer will be the last line of the file.

Then you printf the last_product , like this:

case 1:

  p_datos = fopen("datos.txt", "r");
  if (p_datos == NULL )
  {
    exit(1);
  }
  if (p_datos != NULL )
  {
    char last_product[100];
    while (fgets(last_product, 100, p_datos) != NULL)
        ;
    printf(
        "CODIGO DE PRODUCTO\tNOMBRE DE PRODUCTO\tPRECIO DE PRODUCTO\n\n\n");
    printf("%s", last_product);
    fclose(p_datos);
    puts("\n\n");
  }

I haven't analyzed or tested your entire code, but this should be enough to get you going.

PS: If it pleases you, rather than just printing last_product like I've done, you can sscanf from it into your struct and then print the struct contents.