C Programming - passing a pointer to an array
How to pass the value of a pointer to a structure array;
For example, on txt, I have this:
John Doe;xxxx@hotmail.com;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 do I pass the value of ap_name, ap_email, ap_phone to a struct? And, should all these pointers be used?
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The name and email address are relatively simple; 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 ap_name
to into the structure name field. No more 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 ap_name
is less than 99 - strlen (ap_name) nul characters (ASCII 0). The same for email:
strncpy(persons[i].email, ap_email, sizeof persons[i].email - 1);
Note that this assumes that the lengths of ap_name and ap_email will always be less than the target buffers; as written, your code pretty much guarantees this, but additional sanity checking might be a bad idea.
As with a phone number, a regular int may not (and most likely will not) be wide enough to hold a 10-digit number, provided you store the area or extension code (minimum range guaranteed by locale [-32767,32767]
). Not to mention, phone numbers are usually represented by non-numeric characters like (999)-999-9999
. You can also save this information as a string.
EDIT
Another alternative to a phone number is to use a wider numeric type (preferably unsigned):
struct PERSON {
...
unsigned long phone;
...
};
and then convert the string with strtoul()
:
persons[i].phone = strtoul(ap_phone, NULL, 10);
The library function strtoul()
converts the string representation of a number to an equivalent numeric value.
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Use strncpy
to copy a string to the corresponding structure element.
You might want to make your element a phone
string rather than an int (phone numbers usually contain non-numeric characters). If it really should be an int, use atoi
or strtol
to convert the string ap_phone
to int and then just assign that value to the phone.
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I'm not sure what you are asking, but:
When you have a structure, each member is only accessible with. Operator.
persons[0].name
persons[3].email
persons[10].phone
All valid operators receive the 0th person name, third party email address, or the 10th person's phone number. Each of them is a separate variable that can be thought of as something else.
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