Why this union is deleting the 1st records in arrays in the c code?

Answer 1

Do you know what union means in C? Your union doesn't have 3 members. Your union has 4 members. Among those 4 members, how many do you want to store values in?

Why didn't you ask your TA?

Answer 2

You may be misunderstanding the purpose of a union.

A union is typically used to store one item that may be in one of several forms. For example:

// Define an array of 20 employees, each identified either by name or ID.
union ID {
    char name[10];   // ID may be a name up to 10 chars...
    int  serialNum;  // ... or it may be a serial number.
} employees[20];

// Store some data.
employees[0].serialNum = 123;
strcpy(employees[1].name, "Manoj");

The critical difference between a struct and a union is that a struct is an aggregate of many pieces of data, but a union is an overlayment: you may store only one of the elements because they all share the same memory. In the example above, each element in the employees[] array consists of 10 bytes, which is the smallest amount of memory that can hold either 10 chars or 1 int. If you reference the name element, you can store 10 chars. If you reference the serialNum element, you can store 1 int (say 4 bytes) and cannot access the remaining 6 bytes.

So I think you want to use different, separate structures to represent the family members. What you've done appears to be cramming several square pegs into one round homework assignment. :-)

Note for advanced readers: please don't mention padding and word alignment. They're probably covered next semester. :-)

Answer 3

You need to read this question about unions. You want something more like:

struct family {
    struct name { 
        int gender;
        int married;
        blah
    } names;
    union {
        struct male { blah } male_ancestor;
        struct female_unmarried { blah } female_unmarried_ancestor;
        struct female_married { blah } female_married_ancestor;
    };
}

then you can test family.names.gender and family.names.married to determine which member of the union to use.