Data by reference instead of value - c

Question

I am trying to make a program that has a menu and it has an option to set the "current" date. I can define the date and it will stay until the program shuts down. I've got another method to get the date, by asking the user the date when linking a person to it, the problem is that it wont go on the main data on the main menu. It will only be the data for the .date on the person structure, I guess I explained it well. I've tried many ways and I really can't figure it out, if someone can help me out...
typeData readData() {
int val;
typeData data;
do {
printf("Day: ");
data.day = readInteger(MIN_DAYS, MAX_DAYS);
printf("Month: ");
data.month = readInteger(MIN_MONTH, MAX_MONTH);
printf("Year: ");
data.year = readInteger(MIN_YEAR, MAX_YEAR);
val = validateData(data);
if(val == 0) {
printf("The data is not valid.\n");
}
} while (val == 0);
return data;
}
I think I need to get it by reference but I'm trying for some time already and can't do it. Thanks everyone.

Answer 1

While it's legal C, passing structs by value and returning them is usually not the best way. Consider:
void
readData(typeData *data)
{
int val;
do {
printf("Day: ");
data->day = readInteger(MIN_DAYS, MAX_DAYS);
printf("Month: ");
data->month = readInteger(MIN_MONTH, MAX_MONTH);
printf("Year: ");
data->year = readInteger(MIN_YEAR, MAX_YEAR);
val = validateData(data);
if (val == 0) {
printf("The data is not valid.\n");
}
} while (val == 0);
}
UPDATE:
Here is a sample main program plus sample changes to validateData:
int
validateData(typeData *data)
{
int data_valid = 1;
// check for error
// this is whatever checks you already do ...
if (data->... != ...)
data_valid = 0;
return data_valid;
}
int
main(int argc,char **argv)
{
typeData main_data;
readData(&main_data);
// do something useful with the data [or transform it, etc]
processData(&main_data);
// print some results
printData(&main_data);
return 0;
}
UPDATE #2:
Here's a modified [partial] program, based on your latest example. I had to guess at the overall organization, but, at least it has the necessary changes to menuPrincipal:
int
validateData(typeData *data)
{
int data_valid = 1;
// check for error
// this is whatever checks you already do ...
if (data->... != ...)
data_valid = 0;
return data_valid;
}
char
menuPrincipal(typeDate *date)
{
char option;
if (date->day == 0 && date->month == 0 && data->year == 0) {
printf("Date not set yet.\n");
}
else {
printf("Date: %d/%d/%d", date->day, date->month, date->year);
}
// more stuff
return option;
}
int
main(int argc,char **argv)
{
typeData main_data;
char option;
while (1) {
readData(&main_data);
option = menuPrincipal(&main_data);
switch (option) {
case 'a': // do something
break;
case 'b': // do something else
break;
default:
printf("unknown option: '%c'\n",option);
break;
}
}
return 0;
}
UPDATE #3:
Based on your latest comment, I think I see what you're having trouble with. I've taken your latest code snippet and updated:
// your original code -- this no longer works because readData is now void
if (data->ano == 0 && data->mes == 0 && data->dia == 0) {
Blah[*Bleh].date = readData(*data);
}
// one possibility -- but it does _not_ update "data"
if (data->ano == 0 && data->mes == 0 && data->dia == 0) {
readData(&Blah[*Bleh].date);
}
// this is more likely what you want -- it updates _both_:
if (data->ano == 0 && data->mes == 0 && data->dia == 0) {
readData(data);
Blah[*Bleh].date = *data;
}

Answer 2

It works now, I was using
val = validateDate(&date)
on the original function for readData, now I changed it to
val = validateDate(date)
and it works!
I just don't know why I need to use date instead of &date, I thought that if I was passing the parameters by reference I needed a '&' symbol.