CODEWITHSUNDEEP
carraysstructinitializationunions
user1692517
user1692517

Reputation: 1152

Trouble Initializing a element of an array of Structs that has a Union

I'm having trouble initializing a struct that has a union in it also. I tried following a few guides and it seems like I'm it correctly, obviously not though if it's not working.

I have the following header

#ifndef MENU_H_
#define MENU_H_

typedef struct student{
    int gpa;
    float tuitionFees;
    int numCourses;
}student;

typedef struct employee{
    float salary;
    int serviceYears;
    int level;
}employee;

typedef struct person{
    char firstName[20];
    char familyName[20];
    char telephoneNum[10];
    int type; // 0 = student / 1 = employee;
    union{
        employee e;
        student s;
    };
}newPerson;

#endif

And then this is what I'm having trouble with

newPerson person[MAX_PERSONS];
person[1] = {"geo", "dude", "6136544565", 0, {3, 2353, 234}};

when I try to initialize person[1], I get the following error

error: expected expression before ‘{’ token

I was wondering what the cause of this might be? Does not seem like I'm missing a brace, I also tried to remove the inner braces but it still does not work. Any help would be very much appreciated. Thank you

Upvotes: 2

Views: 88

Answers (1)

M Oehm
M Oehm

Reputation: 29126

The error message refers to the first open brace. You can initialise an object with the curly-brace syntax, but you cannot assign it. In other words, this works:

int array[3] = {0, 8, 15};

but this doesn't:

array = {7, 8, 9};

C99 introduced compound literals, which look like a combination of type cast and initialiser, e.g.:

int *array;

array = (int[3]){ 1, 2, 3 };

C99 also introduced designated initialises, where you can specify an array index or a struct or ´union` field you want to initialise:

int array[3] = {[2] = -1};        // {0, 0, -1}
employee e = {.level = 2};        // {0.0, 0, 3}

If we apply these features to your problem, we get something like:

enum {
    STUDENT, EMPLOYEE
};

typedef struct student{
    int gpa;
    float tuitionFees;
    int numCourses;
} student;

typedef struct employee{
    float salary;
    int serviceYears;
    int level;
} employee;

typedef struct person{
    char firstName[20];
    char familyName[20];
    char telephoneNum[10];
    int type;
    union {
        employee e;
        student s;
    } data;
} person;

int main()
{
    person p[3];

    p[0] = (person) {
        "Alice", "Atkins", "555-0543", STUDENT,
        .data = { .s = { 20, 1234.50, 3 }}
    };

    p[1] = (person) {
        "Bob", "Burton", "555-8742", EMPLOYEE,
        .data = { .e = { 2000.15, 3, 2 }}
    };    

    return 0;
}

I have introduced a name for the union, so that I can refer to it in the initialiser.

Upvotes: 5

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