C Programming - Passing a pointer to array

Question

How do I pass a pointer value to an array of the struct;

For example, on a txt I have this:

John Doe;[email protected];214425532;

My code:

typedef struct Person{
    char name[100];
    char email[100];
    int phone;
}PERSON;

int main(){
   PERSON persons[100];
    FILE *fp;
    char *ap_name;
    char *ap_email;
    char *ap_phone;
    char line[100];
    fp=("text.txt","r");
    if(fp==NULL){
        exit(1);
    }
    else{
        fgets(line,100,fp);
        ap_name=strtok(line,";");
        ap_email=strtok(NULL,";");
        ap_phone=strtok(NULL,";");
    } 
    return 0;
}

My question is how can I pass the value of ap_name, ap_email, ap_phone to the struct? And, do I need to use all of these pointers?

Try man strcpy. And probably strtol if you need the phone number as an integer (which I personally think is a bad idea, but to each his own). — Carl Norum
– Carl Norum, Commented May 5, 2010 at 18:02
You can't pass anything to a struct. It's a data structure, not a procedure. You can assign to members of the struct. — WhirlWind
– WhirlWind, Commented May 5, 2010 at 18:04

Paul R · Accepted Answer · 2010-05-05 18:36:24Z

2

Use strncpy to copy a string to its corresponding struct element.

You might want to make your phone element a string rather than an int (phone numbers typically contain non-numeric characters). If it really has to be an int then use atoi or strtol to convert the ap_phone string to an int, and then just assign this value to phone.

edited May 5, 2010 at 18:36

answered May 5, 2010 at 18:03

Paul R

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8 Comments

Carl Norum Over a year ago

Assigning a string to an integer?

Jonathan Leffler Over a year ago

You can only assign to phone after converting the string to a number.

user166390 Over a year ago

+1 for "You might want to make your phone element a string rather than an int (phone numbers typically contain non-numeric characters)."

user50049 Over a year ago

I think you meant strncpy() ?

Paul R Over a year ago

@Tim: yes, I guess I did mean strncpy. ;-)

|

John Bode · Accepted Answer · 2010-05-05 19:28:26Z

Name and email are relatively easy; just use strcpy (or strncpy);

strncpy(persons[i].name, ap_name, sizeof persons[i].name - 1);

This will copy the contents of the string pointed to by ap_name into the name field of the struct. At most sizeof persons[i].name - 1 (100 - 1, or 99) characters will be copied into persons[i].name, and if the length of the string pointed to by ap_name is less than that, then 99 - strlen(ap_name) nul characters (ASCII 0) are appended. Same thing for email:

strncpy(persons[i].email, ap_email, sizeof persons[i].email - 1);

Note that this assumes that the length of ap_name and ap_email will always be less than the destination buffers; as written, your code pretty much guarantees this, but extra sanity checking may not be a bad idea.

As for the phone number, a regular int may not be (and most likely won't be) wide enough to hold a 10-digit number, assuming you're storing area code or extensions (the minimum range guaranteed by the language standard is [-32767,32767]). Not to mention that phone numbers are generally represented with non-numeric characters, such a (999)-999-9999. You may want to store this information as a string as well.

EDIT

Another alternative for the phone number is to use a wider numeric type (preferably unsigned):

struct PERSON {
   ...
   unsigned long phone;
   ...
};

and then convert the string using strtoul():

persons[i].phone = strtoul(ap_phone, NULL, 10);

The strtoul() library function will convert a string representation of a number into the equivalent numerical value.

Andrei Krotkov · Accepted Answer · 2010-05-05 18:40:40Z

0

I'm not sure whether this is what you're asking, but:

When you have a structure, each member is just accessed with the . operator.

persons[0].name
persons[3].email
persons[10].phone

Are all valid operators to get the 0th person's name, the 3rd person's email or the 10th person's phone number. Each of those is a separate variable that can be treated as anything else.

answered May 5, 2010 at 18:40

Andrei Krotkov

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1 Comment

Pedro Over a year ago

i know that...what i want is to pass the value of pointer to the struct

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