Built-in Data Types

Test Program

int main()
{
    cout << "Size of char : " << sizeof(char)
      << " byte" << endl;
    cout << "Size of int : " << sizeof(int)
      << " bytes" << endl;
    cout << "Size of short int : " << sizeof(short int)
      << " bytes" << endl;
    cout << "Size of long int : " << sizeof(long int)
       << " bytes" << endl;
    cout << "Size of signed long int : " << sizeof(signed long int)
       << " bytes" << endl;
    cout << "Size of unsigned long int : " << sizeof(unsigned long int)
       << " bytes" << endl;
    cout << "Size of float : " << sizeof(float)
       << " bytes" <<endl;
    cout << "Size of double : " << sizeof(double)
       << " bytes" << endl;
    cout << "Size of wchar_t : " << sizeof(wchar_t)
       << " bytes" <<endl;

    return 0;
}

Output:

Struct

Note that there are paddings if a bigger data type is right before one with smaller size.

Test Program 1

int main()
{

    struct A {

        // sizeof(int) = 4
        int x;
        // Padding of 4 bytes

        // sizeof(double) = 8
        double z;

        // sizeof(short int) = 2
        short int y;
        // Padding of 6 bytes
    };

    cout << "Size of struct: " << sizeof(struct A);

    return 0;
}

Output:

Test Program 2

int main()
{

    struct B {
        // sizeof(double) = 8
        double z;

        // sizeof(int) = 4
        int x;

        // sizeof(short int) = 2
        short int y;
        // Padding of 2 bytes
    };

    cout << "Size of struct: " << sizeof(struct B);

    return 0;
}

Union

Union is as large as the largest member of it, including the padding size.

int main() {
    // "At least as big as the largest contained type", some paddings are added
    union {
        char all[13];
        int foo;
    } record;

    printf("%d\n",sizeof(record.all));
    printf("%d\n",sizeof(record.foo));
    printf("%d\n",sizeof(record));

}

Output:

References

1. https://www.geeksforgeeks.org/c-data-types/
2. https://www.geeksforgeeks.org/is-sizeof-for-a-struct-equal-to-the-sum-of-sizeof-of-each-member/
3. https://stackoverflow.com/questions/740577/sizeof-a-union-in-c-c