CODEWITHSUNDEEP
cstructscanf
Tuco
Tuco

Reputation: 1052

Using scanf to create new struct object

Hi I'm using to create a simple program that contains a list of Users (based on the struct below), and I'm trying to create new users based on user input, where I ask for each property seperately using scanf. But I'm having trouble with the structs limitations, for example id should be at max 10 chars and nome can have a max of 25 chars. Here's my code for more context:

struct user {
  char id[10];
  char name[25];
  char group;
  float score;
};

struct user list[25];
int registered = 0;

void createNewUser() {
  struct user *userPtr, newUser;
  userPtr = &newUser;

  printf("\nId: ");
  scanf("%10s", &(*userPtr).id);
  printf("\nName: ");
  scanf("%25s", &(*userPtr.name);
  printf("\nGroup: ");
  scanf("%c", &(*userPtr).group);
  printf("\nScore: ");
  scanf("%f", &(*userPtr).score);

  insert(newUser);

  printf("%10s\n", list[0].id);
  printf("%25s\n", list[0].name);
  printf("%c\n", list[0].group);
  printf("%.1f\n", list[0].score);
}

void insert(struct user newUser) {
  if (registered < 25){
    list[registered] = newUser;
    registered += 1;
  }
}

With the code I presented above, if I type more than 10 chars for the first input, the next 2 are ignored. And my 3rd scanf is always ignored, the one for group. Can anyone here help me out with this?

Upvotes: 0

Views: 802

Answers (1)

Pablo
Pablo

Reputation: 13580

The problem with scanf is that when it stops converting characters and there are more in the input buffer (because the user entered more than you anticipated), then scanf will leave those characters there. Specially the newline character (inputed when the user presses ENTER) remains in the input buffer, which causes problems to subsequent calls of scanf that read characters or strings. So in this case you have to "clean" the input buffer, so that the next scanf does not consume the left overs of the previous scanf calls.

You can use this function after every scanf:

void clean_stdin(void)
{
    int c;
    while((c = getchar()) != '\n' && c != EOF);
}

Then you can do:

printf("\nId: ");
scanf("%10s", (*userPtr).id); // no need for &, id is char[]
clean_stdin();

printf("\nName: ");
scanf("%25s", (*userPtr).name); // same here
clean_stdin();

printf("\nGroup: ");
scanf("%c", &(*userPtr).group);
clean_stdin();

printf("\nScore: ");
scanf("%f", &(*userPtr).score);

Also note that the way you are if the maximal length of the ID is 10, then the buffer must be of length 11, because in C you need to terminate the strings with the '\0'-terminating byte. So change your structure to this:

struct user {
  char id[11];
  char name[26];
  char group;
  float score;
};

Also bear in mind, using a pointer like this

struct user *userPtr, newUser;
  userPtr = &newUser;

  printf("\nId: ");
  scanf("%10s", (*userPtr).id);
  ...

is not necessary, it actually makes the code harder to read. You can do:

void createNewUser() {
    struct user newUser;

    printf("\nId: ");
    scanf("%10s", newUser.id);
    clean_stdin();
    ...

    printf("\nScore: ");
    scanf("%f", &newUser.score);
    ...
}

Upvotes: 3

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