How do I add a string to a struct using a function?

Question

I made a parking system where I entered the information of the vehicles using the void function. But I don't know how to put the strings into the struct by using void.

And here is my code. Where is my mistake?

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

struct car {
  char plate[10];
  char model[20];
  char color[10];
};

void main() {

  struct car c[4];

  AddCar(c[0], "43ds43", "ford", "blue");
  ShowCar(c[0]);

  return 0;
}
// I guess my mistake is here
void AddCar(struct car c, char p[10], char m[10], char r[10]) {
  strcpy(c.plate, p);
  strcpy(c.model, m);
  strcpy(c.color, r);
}

void ShowCar(struct car c) {
  printf("Plate: %s   Model: %s  Color: %s\n-------", c.plate, c.model, c.color);
}

Adrian Mole · Accepted Answer · 2020-04-13T20:23:22.783

There are a number of errors in your code! To address the 'other' ones first:

You need to provide function prototypes for AddCar and ShowCar before you use them, or the compiler will assume they return int and then complain when it sees the actual definitions.
Your main function (properly) returns 0 but it is declared as void - so change it to int main(...).

And the 'real' problem: you are passing your car structure to AddCar by value - which means a copy is made, then passed to the function. Changes to that copy will not affect the variable in the calling module (i.e. in main). To fix this, you need to pass a pointer to the car struct, and use the -> operator (in place of the . operator) in that function.

Here's a 'fixed' version of your code, with comments added where I've made significant changes:

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

struct car {
    char plate[10];
    char model[20];
    char color[10];
};

// Add your functions' prototypes before you use them...
void AddCar(struct car *c, char p[10], char m[10], char r[10]);
void ShowCar(struct car c);

int main() // If you return an int, you must declare that you do!
{
    struct car c[4];
    // Here, we pass a pointer to `c[0]` by adding the `&` (address of)...
    AddCar(&c[0], "43ds43", "ford", "blue");
    ShowCar(c[0]);
    return 0;
}

void AddCar(struct car *c, char p[10], char m[10], char r[10])
{                   // ^ To modify a variable, the function needs a POINTER to it!
    strcpy(c->plate, p);
    strcpy(c->model, m);  // For pointers to structures, we can use "->" in place of "."
    strcpy(c->color, r);
}

void ShowCar(struct car c)
{
    printf("Plate: %s   Model: %s  Color: %s\n-------", c.plate, c.model, c.color);
}

Feel free to ask for further clarification and/or explanation.

Also, if I want to add the time inside the struct, how should I write it in void?Thanks for the comment — MLHYLMZ, Apr 13 '20 at 20:18
@MLHYLMZ What format/type would your time field take? An integer (number of minutes or seconds) or something else? — Adrian Mole, Apr 13 '20 at 20:20
I want add current time in string or integer it does not matter.When I say ShowCar, I want it to write the current time separately.Example: Plate: 12gds43 Model:Toyota Color:Black Added time: 22:32 — MLHYLMZ, Apr 13 '20 at 20:32
[This answer](https://stackoverflow.com/a/1442131/10871073) may help you get the time as a string. — Adrian Mole, Apr 13 '20 at 20:35
... you can add a `time_t` member to your `car` structure, set that value in `AddCar`, then format it as described in that answer in the `ShowCar` function. — Adrian Mole, Apr 13 '20 at 20:39

score 0 · Answer 2 · answered Apr 13 '20 at 20:06

0

You're copying struct car c. Pass it as pointer:

 AddCar(&c[0], "43ds43", "ford", "blue");
 // ...
 void AddCar(struct car *c,char p[10],char m[10],char r[10]) {
    strcpy(c->plate,p);
    strcpy(c->model,m);
    strcpy(c->color,r);
 }

answered Apr 13 '20 at 20:06

a1ezh

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How do I add a string to a struct using a function?

2 Answers2