Consider the following C declaration and assume that the machine has 1-byte characters, 2-byte short, 4-byte integers, 4-byte single-precision floating point numbers, 4-byte pointers, 8-byte double- precision floating-point numbers, and the compiler does not reorder fields and leaves no memory gaps. You may consider all other data types as 8-byte. union UI ( int value; char code; double data; void pointer; }; union U2 ( float func; short small [2]; }; union U3 ( B; char text; long long number; }; union U4 ( char name [6]; unsigned int id; }; struct S ( int index; union Ui item; union U4 person; void next;

Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
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**Educational Text on C Declaration and Memory Layout**

---

Consider the following C declaration and assume the following for the machine:

- **1-byte characters**
- **2-byte shorts**
- **4-byte integers**
- **4-byte single-precision floating-point numbers**
- **4-byte pointers**
- **8-byte double-precision floating-point numbers**

The compiler does not reorder fields and leaves no memory gaps. All other data types are considered as 8-byte:

```c
union U1 {
    int value;
    char code;
    double data;
    void* pointer;
};

union U2 {
    float func;
    short small[2];
};

union U3 {
    char text;
    long long number;
};

union U4 {
    char name[6];
    unsigned int id;
};

struct S {
    int index;
    union U1 item;
    union U4 person;
    void* next;
} s;
```

**Questions to Consider:**

1. **How many bytes does each `union` declared in the code and `struct S` occupy?**

2. **If the memory address of `S` starts from 3000, what are the start addresses of `S.item.pointer` and `S.person.name[2]`?**

3. **If the compiler uses a simple memory alignment mechanism that aligns variables to 8-byte boundaries, what will be the size of `S`?**

---

**Explanation and Analysis:**

1. **Union Sizes:**
   - Each union is sized according to its largest member.
     - `union U1`: Largest member is `double data` (8 bytes).
     - `union U2`: Largest member is `func` or `small[2]` (4 bytes each, totaling 8 bytes).
     - `union U3`: Largest member is `number` (8 bytes).
     - `union U4`: Largest member is `id` (4 bytes, but in practice unions are aligned to larger sizes).

2. **Struct S Size:**
   - Includes size of `index` (4 bytes), `union U1` (8 bytes), `union U4` (aligned to 8 bytes), and `next` (4 bytes).
   - Alignment adjustments may lead to additional padding.

3. **Address Calculations:**
   - Given starting address 3000, calculate addresses based on sizes and alignments.

This exercise emphasizes understanding memory
Transcribed Image Text:**Educational Text on C Declaration and Memory Layout** --- Consider the following C declaration and assume the following for the machine: - **1-byte characters** - **2-byte shorts** - **4-byte integers** - **4-byte single-precision floating-point numbers** - **4-byte pointers** - **8-byte double-precision floating-point numbers** The compiler does not reorder fields and leaves no memory gaps. All other data types are considered as 8-byte: ```c union U1 { int value; char code; double data; void* pointer; }; union U2 { float func; short small[2]; }; union U3 { char text; long long number; }; union U4 { char name[6]; unsigned int id; }; struct S { int index; union U1 item; union U4 person; void* next; } s; ``` **Questions to Consider:** 1. **How many bytes does each `union` declared in the code and `struct S` occupy?** 2. **If the memory address of `S` starts from 3000, what are the start addresses of `S.item.pointer` and `S.person.name[2]`?** 3. **If the compiler uses a simple memory alignment mechanism that aligns variables to 8-byte boundaries, what will be the size of `S`?** --- **Explanation and Analysis:** 1. **Union Sizes:** - Each union is sized according to its largest member. - `union U1`: Largest member is `double data` (8 bytes). - `union U2`: Largest member is `func` or `small[2]` (4 bytes each, totaling 8 bytes). - `union U3`: Largest member is `number` (8 bytes). - `union U4`: Largest member is `id` (4 bytes, but in practice unions are aligned to larger sizes). 2. **Struct S Size:** - Includes size of `index` (4 bytes), `union U1` (8 bytes), `union U4` (aligned to 8 bytes), and `next` (4 bytes). - Alignment adjustments may lead to additional padding. 3. **Address Calculations:** - Given starting address 3000, calculate addresses based on sizes and alignments. This exercise emphasizes understanding memory
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