Array of Multiple Structs

Question

I have a void array and i want inside it to enter structs.

No i don't mean something like that :

struct pinx
{
  int n;

};
struct pinx *array;

I want a dynamic array like that :

struct data
{
  void **stack;
}exp1;

To have as members multiple structs like these structs:

struct student
{
 char flag;
 char name[50];
 int sem;
};

struct prof
{
 char flag;
 char name[50];
 int course;
};

Flag is used for telling the program if the array in that specific position has a struct from stud or prof.

Also an image to make it more clear for you. enter image description here

I tried to connect the array with structs by declaring an array to both of the structs but it doesn't work for both only for one struct.

struct student *student_array;
struct prof *prof_array;
exp1.stack = (void *)student_array;
exp1.stack = (void *)prof_array;

Are you allocating memory anywhere? Do you want to put both objects in the same position? — imreal
– imreal, Commented Mar 25, 2014 at 18:55
Yes i am allocating memory and no i don't want in the same position i want the one or the other . For exapmple : exp1.stack[0] for student , exp1.stack[1] for professor etc. — Manuel Pap
– Manuel Pap, Commented Mar 25, 2014 at 18:57
In that case you should assign them accordingly. exp1.stack[0] = (void *)student_array; Although, using a union like it is explained in the answer below is better, specially for identical size structures. — imreal
– imreal, Commented Mar 25, 2014 at 19:03

Sergey Kalinichenko · Accepted Answer · 2014-03-25 18:56:55Z

3

C provides a union type for dealing with situations like this. You can define a struct that "mixes" students and professors, and keeps a flag so that you know which one it is:

struct student {
    char name[50];
    int sem;
};
struct prof {
    char name[50];
    int course;
};
struct student_or_prof {}
    char flag;
    union {
        struct student student;
        struct prof prof;
    }
};

A union will allocate enough memory to fit any one of its members.

Now you can make an array of student_or_prof, populate it, and use it to store a mixture of professors and students:

student_or_prof sop[2];
sop[0].flag = STUDENT_TYPE;
strcpy(sop[0].student.name, "quick brown fox jumps");
sop[0].sem = 123;
sop[1].flag = PROF_TYPE;
strcpy(sop[1].prof.name, "over the lazy dog");
sop[1].course = 321;

answered Mar 25, 2014 at 18:56

Sergey Kalinichenko

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