使用动态分配（malloc 或 calloc）在具有不同座位数的几辆公共汽车中预留座位的程序

Question

I have to make a program that reserves a seats in a few buses (every bus have a different number of seats). I have to use malloc or calloc. It has to store info about name and surname and assign it to a seat. When seat are already occupied it has to give an info "seat already taken". It also has to error handling. I am begginer and I don't know what to do.

#include <stdlib.h>

#define max_name 32

int main()
{

    int n_buses,n_seats,zm;
    char*** tab;
    printf("Number of buses:");
    scanf("%d", &n_buses);

    tab=calloc(n_buses,sizeof(char**));

    for(int i=0;i<n_buses;i++)
    {
        printf("Number of seats in bus %d: ", i+1);
        scanf("%d", &zm);

        tab[i]=calloc(zm,sizeof(char*));
    }

    for(int i=0;i<n_buses;i++)
    {
        for(j=0;j<max_name;j++)
        {
            tab[i][j]=calloc(max_name,sizeof(char));
        }
    }
 for(i=0;i<n_buses;i++)
    {
        if(tab[i]) free(tab[i]);
    }

    if(tab) free(tab);

    return 0;
}```

Answer 1

Take a step back away from this pointer-to-pointer-to-pointer and consider what would make an easy to use data type instead. You have buses, seats and passengers, so it makes sense to come a couple of structs to handle the abstraction for that:

typedef struct
{
  char* forename;
  char* lastname;
} passenger_t;

typedef struct
{
  int total_seats;
  passenger_t seat[];
} bus_t;

The last struct uses a trick called flexible array member to allow a variable-sized array at the end of a struct. You'd allocate memory for it as:

int seats = 100;
bus_t* my_bus = calloc( seats, sizeof(*my_bus) + sizeof(passenger_t[seats]) );
if(my_bus == NULL) { /* handle errors */ }

my_bus->total_seats = seats;

Now every seat is represented by an allocated passenger_t item in the seat array, each item with two pointers set to null by calloc (malloc wouldn't set them to null). You can use this to keep track of if a seat is free or taken.

Add a passenger:

if(n >= my_bus->total_seats)  // check that input is valid
{ 
  /* error handling */
}

if(my_bus->seat[n].forename != NULL)
{
  my_bus->seat[n].forename = ... /* allocate room for forename then strcpy to it*/

  my_bus->seat[n].lastname = ... /* allocate room for lastname then strcpy to it*/
}

Note how we only have one array here and one level of indirection, so this code turns out much easier to read and maintain.