Question 1

C programming — evaluate this self-referential structure declaration for correctness.  struct emp {  int ecode;  struct emp e; / pointer to the same struct type (self-reference) */ };  Is there any language error in the declaration above?

Accepted Answer

Introduction / Context: Self-referential structures are common in linked lists and trees. The question checks whether a struct can contain a pointer to its own type within its definition. Given Data / Assumptions: The member e is declared as struct emp *. No storage is allocated yet; only the type layout is set. Concept / Approach: C permits a struct to contain pointers to its own (incomplete) type in the same declaration. What is not permitted is embedding an instance (by value) of the same struct inside itself, which would make the size infinite. Pointers are fixed-size and therefore allowed. Step-by-Step Solution: 1) During the struct's declaration, the tag struct emp becomes known.2) A pointer to struct emp is a complete type size-wise, even if the pointed-to type is incomplete.3) Therefore the declaration is valid; no compile-time error occurs. Verification / Alternative check: This pattern underlies singly and doubly linked lists. Code that later allocates nodes and links e to other struct emp values compiles and runs normally. Why Other Options Are Wrong: Structure declaration error: Incorrect; this is the idiomatic style. Linker error: There is no external symbol involved here. Undefined behavior: Only occurs if you dereference an uninitialized pointer at runtime, not from the declaration itself. Common Pitfalls: Confusing self-referential pointers (valid) with embedding the struct by value (invalid). Final Answer: No error

Question 2

C programming — identify the compile-time issue in this bit-field struct definition and sizeof usage.  #include<stdio.h>  int main() {  struct a  {  float category:5; /* bit-field on float /  char scheme:4; / small bit-field on char (non-standard ex…

Accepted Answer

Introduction / Context: This item again tests the rule that bit-fields must be of integer type or _Bool. A float bit-field violates the language requirements in standard C. Given Data / Assumptions: struct a declares float category:5; and char scheme:4; Program prints sizeof(struct a). Concept / Approach: Bit-fields of floating types are not permitted. Some compilers may also restrict the underlying integer types for bit-fields; _Bool, signed int, and unsigned int are the portable choices. Therefore the error is specifically the float bit-field line, not the sizeof or printf call. Step-by-Step Solution: 1) Inspect member types: float for a bit-field violates the rule.2) Compilation fails before evaluating sizeof.3) If changed to unsigned int category:5;, the program compiles and sizeof can be printed. Verification / Alternative check: Replace float with unsigned int; compile succeeds confirming the diagnosis. Why Other Options Are Wrong: Invalid structure member in printf: printf is fine; it prints an int cast of sizeof. No error: Contradicted by the rule on bit-field types. sizeof on incomplete type: struct a is complete at the point of sizeof. Common Pitfalls: Assuming any type can be a bit-field, or blaming printf instead of the declaration. Final Answer: Error in this float category:5; statement

Question 3

C programming — spot the error related to forward declarations and prototypes. #include #include void modify(struct emp*); /* prototype uses struct emp before its declaration / struct emp { char name[20]; int age; }; int mai…

Accepted Answer

Introduction / Context: This question examines how C handles tags (struct names) with respect to declarations and prototypes. Using a structure tag in a function prototype before the tag is declared requires at least a forward declaration of the tag. Given Data / Assumptions: The function prototype void modify(struct emp); appears before struct emp is declared. No forward declaration (struct emp;) precedes the prototype. Concept / Approach: In C, identifiers must be declared before use. A struct tag introduces a distinct namespace. To mention struct emp in a prototype prior to the full definition, you must forward declare it: struct emp; After that, the prototype may use struct emp safely, and the full definition can follow. Step-by-Step Solution: 1) The prototype references struct emp before the compiler has seen any declaration of that tag.2) Without a prior tag declaration, the compiler reports that struct emp is unknown at the prototype.3) Fix: add a forward declaration line struct emp; above the prototype, or move the full struct definition above the prototype. Verification / Alternative check: Adding struct emp; makes the code compile; modify then increments age by 2 and the program prints "Sanjay 37". Why Other Options Are Wrong: Structure definition error: The definition itself is fine. No error: Violates declaration-before-use for the tag in standard C. Linker error: The issue is purely compile-time, not linking. Common Pitfalls: Assuming prototypes can reference undeclared tags; forgetting that struct tags form their own namespace and need forward declarations when used early. Final Answer: Error: in prototype declaration unknown struct emp

Question 4

C programming on a 16-bit platform — analyze this bit-field width for validity.  #include<stdio.h>  int main() {  struct bits  {  int i:40; /* 40 bits requested in a 16-bit environment */  } bit;   printf("%d", (int)sizeof(bit));  return 0; }  What …

Accepted Answer

Introduction / Context: Bit-field widths cannot exceed the number of bits available in the underlying type. On a 16-bit platform, the width of int is typically 16 bits. Requesting 40 bits is not representable and must be rejected by the compiler. Given Data / Assumptions: Assume int is 16 bits (typical for the stated platform). Member declaration uses int i:40. Concept / Approach: For a bit-field of type int, the maximum width is the number of value bits that type can store (implementation-defined but generally the bit width of int). If the requested width exceeds that, it is ill-formed or at least a constraint violation for that target. Step-by-Step Solution: 1) Determine int width on the target: 16 bits in this scenario.2) Compare requested width: 40 > 16, so it cannot fit.3) Compiler emits an error about an excessively large bit-field. Verification / Alternative check: Changing to unsigned int i:15; compiles. Using a wider implementation type (e.g., long) on wider platforms may also work, but not 40 bits on a 16-bit int. Why Other Options Are Wrong: 2 or 4: These are guesses at sizeof and miss the primary compile-time constraint. Invalid member access: Access is not the issue; the declaration is. Common Pitfalls: Assuming bit-field widths are portable across platforms; forgetting the underlying type's width limits. Final Answer: Error: Bit field too large

Question 5

C language concept — are nested unions allowed in C?  Statement: Nested unions are allowed.

Accepted Answer

Introduction / Context: This conceptual question asks whether a union may contain another union (directly or via a member that is itself a union) in standard C. Understanding type composition rules helps in designing compact variant data structures. Given Data / Assumptions: The statement claims nested unions are allowed. No specific code is given; we consider standard C behavior. Concept / Approach: Standard C permits composing structs and unions from other structs and unions. A union member can be another union or a struct, and vice versa. Restrictions apply only to incomplete types and to members that would create infinite recursion by value (but pointers to the same type are fine). Step-by-Step Solution: 1) Recall that structs and unions are aggregate types and may contain other aggregate types as members.2) A union U can have a member union V; the layout reserves enough space for the largest member.3) Self-embedding by value would be invalid due to infinite size, but nesting distinct unions is valid. Verification / Alternative check: Example compiles: union V { int x; float y; }; union U { union V v; int k; } u; This is valid in standard C. Why Other Options Are Wrong: Incorrect / C++ only / extensions only: These contradict the standard's allowance for aggregate nesting. Common Pitfalls: Confusing “nested by value” with “self-referential by pointer”; only the latter avoids infinite size problems. Final Answer: Correct

Question 6

C language concept — can a structure be nested inside another structure?  Statement: A structure can be nested inside another structure.

Accepted Answer

Introduction / Context: Nested (or composite) aggregates are common in data modeling. This item checks whether C permits struct-within-struct design, which is frequently used for grouping related fields hierarchically. Given Data / Assumptions: The statement claims a structure may be nested inside another structure. We consider standard, portable C. Concept / Approach: Standard C allows a struct member to be another struct type by value. This is a straightforward inclusion where the outer struct contains the entire inner struct as a sub-object. Self-embedding by value is not allowed because it would make the size infinite, but nesting different struct types (or the same via pointers) is fine. Step-by-Step Solution: 1) Define an inner struct type before using it as a member of the outer struct.2) Example: struct Address { int pin; }; struct Person { struct Address addr; int age; };3) This compiles and produces a Person whose layout includes the full Address sub-object. Verification / Alternative check: Compilers handle nested structs routinely; accessing fields uses dot chaining like p.addr.pin. Why Other Options Are Wrong: Incorrect / Not allowed: Contradict the standard. Only via pointers: Unnecessarily restrictive; by-value nesting is allowed for different types. Common Pitfalls: Trying to embed a struct inside itself by value (invalid). Use a pointer for self-reference instead. Final Answer: Correct

Question 7

In C programming, can a union contain members of different sizes, and what does that imply for its overall size allocation?

Accepted Answer

Introduction / Context: Unions in C allow multiple members to share the same memory location. This question checks whether union members may have different sizes and what that means for storage and alignment. Given Data / Assumptions: Standard C (C11/C17 rules apply). Union has two or more members of potentially different types. Typical platform alignment rules apply. Concept / Approach: The size of a union is at least the size of its largest member, possibly rounded up for alignment. All members overlap at offset 0, so only one member is meaningfully stored at a time. Step-by-Step Solution: 1) Consider a union with int and double members.2) sizeof(int) might be 4; sizeof(double) might be 8.3) sizeof(union) becomes at least 8 (the larger member), not 4 + 8.4) Different member sizes are allowed; the union allocates memory to accommodate the largest. Verification / Alternative check: Check sizeof for several unions on your platform; it always matches the largest member (with alignment considered). Why Other Options Are Wrong: Option B: Claims equal sizes are required — not true in C. Option C: Not implementation freedom; the standard allows differing sizes. Option D: No packing pragmas are required for this rule. Option E: Same alignment is not a prerequisite for differing sizes. Common Pitfalls: Assuming unions sum member sizes; they do not. Confusing unions with structs regarding layout and storage is common. Final Answer: Correct — union members may have different sizes; the union's size equals that of its largest member.

Question 8

In C, when should you use the -> operator to access members, and what kinds of types does it work with?

Accepted Answer

Introduction / Context: This tests knowledge of C member-access operators: the dot (.) and arrow (->). Understanding when each applies prevents common pointer and syntax errors. Given Data / Assumptions: We are writing standard C. We have both structure and union types available. We may have variables and pointers to these aggregate types. Concept / Approach: Use . with an actual object (non-pointer). Use -> with a pointer to an object. The rule applies identically to structs and unions: . for objects, -> for pointers. Step-by-Step Solution: 1) If s is a struct value, s.member uses .2) If ps is a pointer to struct, ps->member is shorthand for (*ps).member.3) The same rule holds for unions and pointers to unions.4) Therefore, -> is correct when you have a pointer to a struct or union. Verification / Alternative check: Compile small examples: accessing via ps->x compiles if ps is a pointer; using ps.x will fail. Similarly for unions. Why Other Options Are Wrong: Option B: . is required for non-pointer objects, not ->. Option C: Arrays do not use -> for element or member access. Option D: . and -> are not interchangeable. Option E: -> also works with pointers to unions, not only structures. Common Pitfalls: Forgetting to dereference pointers before using . leads to errors; -> already performs that dereference syntactically. Final Answer: Use -> when you have a pointer to a struct or a pointer to a union.

Question 9

C enumerations: choose the correct statement about scope, values, and size control.

Accepted Answer

Introduction / Context: Enumerations (enum) in C define named integer constants. This question checks understanding of default values, scope, and whether the programmer can control the storage size of enum types directly. Given Data / Assumptions: Standard C behavior for enums. Default enumeration values and scope rules apply. Concept / Approach: By default, the first enumerator is 0 and subsequent ones increase by 1 unless you explicitly assign values. Enums can be declared at file scope or block scope. The underlying type is implementation-defined; the programmer cannot portably force its size in classic C versions. Step-by-Step Solution: 1) Check A: C allows explicit assignments but does not require them, so A is wrong.2) Check B: You cannot portably fix enum storage size; B is wrong.3) Check C: Enums can be defined inside a block; the identifiers then have block scope — this is correct.4) Check D: Not all enums are global; scope depends on where they are declared — D is wrong.5) Check E: Default starts from 0, not 1 — E is wrong. Verification / Alternative check: Write a small program with an enum inside a function; its identifiers are not visible outside that block. Why Other Options Are Wrong: Option A: Explicit assignment is optional. Option B: Underlying type is implementation-defined; no portable direct control. Option D: Scope is not automatically global. Option E: Default start is 0, not 1. Common Pitfalls: Assuming enums always start at 1 or thinking they create global names automatically is a frequent misconception. Final Answer: An enumeration can be declared with block scope so its effect is local to that block.

Question 10

In C, does the . operator access members from a structure variable (as opposed to a pointer)?

Accepted Answer

Introduction / Context: Member access syntax is fundamental in C. The . operator and the -> operator apply to different operand types. Given Data / Assumptions: A structure (or union) value. A pointer to such a value may also exist. Concept / Approach: Use . when you have an actual object; use -> when you have a pointer. This rule is identical for structs and unions. Step-by-Step Solution: 1) Let s be a struct value: access as s.member.2) Let ps be a pointer: access as ps->member (i.e., (*ps).member).3) Therefore . is correct for variables, while -> is for pointers. Verification / Alternative check: Compilers enforce this; using . on a pointer produces an error unless you dereference first. Why Other Options Are Wrong: Option B: Reverses the rule. Option C: C has no public/private for structs. Option D: Nesting does not change the operator rule. Option E: . and -> are not interchangeable. Common Pitfalls: Forgetting to dereference pointers or assuming both operators behave the same leads to confusing errors. Final Answer: Correct — use . with a structure (or union) variable, not a pointer.

Question 11

In C, can a structure contain a nested union as one of its members?

Accepted Answer

Introduction / Context: C supports aggregate nesting: structs can contain other structs or unions, and vice versa. This is common in low-level data layouts and protocol headers. Given Data / Assumptions: Standard C features apply. We are defining a struct with multiple members. Concept / Approach: A struct can include a union member directly. The union occupies space within the struct according to its own size and alignment, and the struct’s size reflects all members plus padding. Step-by-Step Solution: 1) Define union U with several fields.2) Define struct S { int x; union U u; }.3) This compiles and is portable; the union is a regular member.4) Access union members via s.u.member (or s_ptr->u.member for pointers). Verification / Alternative check: Write a minimal example and inspect sizeof(S); it includes space for the union and necessary padding. Why Other Options Are Wrong: Option B: The standard permits this nesting. Option C: Unions can have multiple members. Option D: No special pragmas are required. Option E: This is valid in both C and C++. Common Pitfalls: Misunderstanding the difference between struct (members laid out sequentially) and union (members overlapping) when nested. Final Answer: Correct — a structure may include a union member.

Question 12

In C, can bit-fields be declared inside a union?

Accepted Answer

Introduction / Context: Bit-fields compactly represent flags or small integers within a structure. This question checks whether bit-fields are legal inside unions. Given Data / Assumptions: We are in standard C. Bit-field syntax uses a colon with a width in a struct declaration. Concept / Approach: C permits bit-fields only in structures, not in unions. Bit-fields describe allocation within a single struct member record; unions overlay members and therefore do not support bit-field declarations. Step-by-Step Solution: 1) Declare struct with unsigned flags: unsigned a:1; unsigned b:3; — valid.2) Attempt to place the same declarations directly in a union — this is not allowed by the language rules.3) Therefore, use a struct (possibly nested inside a union) if bit-fields are required. Verification / Alternative check: Try compiling a union containing bit-field syntax; conforming compilers will reject it or issue diagnostics. Why Other Options Are Wrong: Option B: Asserts the opposite of the standard rule. Option C/D/E: Add conditions that the standard does not define; they remain disallowed. Common Pitfalls: Confusing what can be placed in unions versus structs. A typical workaround is a union that contains a struct-with-bitfields as one alternative member. Final Answer: Correct — C forbids bit-fields inside unions; use structs for bit-fields.

Question 13

In C, may a structure contain a pointer to the same structure type (self-referential struct)?

Accepted Answer

Introduction / Context: Self-referential structures are fundamental for dynamic data structures such as linked lists, trees, and graphs. C supports this pattern via pointers. Given Data / Assumptions: We are defining a struct type. We intend to include a pointer to the same struct type. Concept / Approach: A struct cannot include a complete object of its own type (infinite size), but it can include a pointer to its own type because pointer size is fixed. This enables recursive data structures. Step-by-Step Solution: 1) struct Node { int data; struct Node *next; } is valid C.2) The pointer permits links between nodes without requiring the struct to know its total size in advance.3) Allocation happens dynamically (e.g., malloc) and nodes are chained via the pointer. Verification / Alternative check: Compile a minimal linked-list node definition; it is universally accepted by C compilers. Why Other Options Are Wrong: Option B: C permits referencing the same type via pointers. Option C: No need to use void *; a typed self-pointer is preferred. Option D: Scope does not limit this capability. Option E: Other members are allowed alongside the pointer. Common Pitfalls: Attempting to embed a complete instance (not a pointer) of the same struct type causes an incomplete type recursion error. Final Answer: Correct — self-referential structures via pointers are allowed.

Question 14

In C, can a structure contain members of similar or dissimilar (heterogeneous) types?

Accepted Answer

Introduction / Context: Structures in C are used to group related data, often of different types. This question checks awareness that structs are heterogeneous aggregates. Given Data / Assumptions: Standard C struct semantics. Mixing types like int, char, double is common. Concept / Approach: A struct can hold fields of different types in sequence. The compiler arranges members with padding to meet alignment requirements; there is no constraint that members be identical types. Step-by-Step Solution: 1) Define struct S { int id; char tag; double value; } — this is valid.2) The size reflects each member plus any padding.3) Access members using . or -> according to whether you have an object or a pointer. Verification / Alternative check: Checking sizeof(S) demonstrates inclusion of heterogeneous members and potential padding. Why Other Options Are Wrong: Option B: No single-type restriction exists. Option C/D: Alignment and member count do not impose such limits. Option E: The concept applies directly to C. Common Pitfalls: Ignoring padding when serializing structures or interfacing with hardware/ABI boundaries. Final Answer: Correct — structures may contain similar or dissimilar types.

Question 15

In C, is it possible to create an array of pointers to structures?

Accepted Answer

Introduction / Context: Arrays and pointers are core to C programming. Many real programs manage collections of dynamically allocated structures using arrays of pointers. Given Data / Assumptions: We have a user-defined structure type. We may need multiple instances managed via pointers. Concept / Approach: C permits arrays of any object type, including pointer types. Therefore, an array of struct pointers is entirely valid and useful when objects are dynamically allocated and shared. Step-by-Step Solution: 1) Declare struct Box { int w, h; };2) Declare struct Box *arr[10]; — an array of 10 pointers to Box.3) Allocate each element separately (e.g., malloc) and assign to arr[i].4) Access via arr[i]->w, arr[i]->h. Verification / Alternative check: Compile and run a small program that fills and reads from an array of struct pointers; it works portably. Why Other Options Are Wrong: Option B: Arrays can hold pointers. There is no such restriction. Option C/D/E: These impose non-existent limitations on member makeup, scope, or length. Common Pitfalls: Forgetting to allocate or free each pointed-to object, and mixing up arr[i].member versus arr[i]->member. Final Answer: Correct — arrays of pointers to structures are fully supported.

Question 16

Given char = 1 byte, int = 2 bytes, and long int = 4 bytes, will the structure below always occupy exactly 7 bytes? Explain considering alignment and padding. struct ex { char ch; int i; long int a; }

Accepted Answer

Introduction / Context: This question evaluates understanding of structure layout, alignment, and padding in C. Even when individual member sizes are known, the overall size must satisfy alignment constraints, which often introduces padding bytes. Given Data / Assumptions: char = 1 byte, int = 2 bytes, long int = 4 bytes. Structure: struct ex { char ch; int i; long int a; }. Conventional alignment: int aligned to 2, long aligned to 4 (typical). Concept / Approach: Members are placed in order. The compiler may insert padding so each member starts at an address multiple of its alignment. The structure size itself is also rounded up to a multiple of the strictest member alignment. Step-by-Step Solution: 1) ch at offset 0 uses 1 byte.2) To align i (2-byte), 1 byte of padding is inserted so i starts at offset 2.3) i occupies 2 bytes (offsets 2–3), so next free offset is 4.4) a (4-byte) is naturally aligned at offset 4 and consumes 4 bytes (4–7).5) Total so far is 8 bytes, not 7, and it also satisfies 4-byte alignment of the largest member. Verification / Alternative check: Use sizeof(struct ex) on a target system with the stated sizes; it will typically report 8 bytes. Different ABIs may differ, but 7 is not generally achievable with standard alignment. Why Other Options Are Wrong: Option A/C/D/E: These ignore alignment rules; changing language mode, warnings, or operators does not alter layout and padding requirements. Common Pitfalls: Simply summing member sizes, forgetting padding between members, and ignoring final structure alignment to the largest member's requirement. Final Answer: No — alignment and padding mean the structure typically occupies 8 bytes, not 7.

Question 17

In C programming, can we directly declare an array whose elements are bit-fields, or must bit-fields be members of a struct only? Explain the correct approach with a short note on why arrays of plain bit-fields are not allowed.

Accepted Answer

Introduction / Context: Bit-fields in C are a special way to pack named fields into an integer type inside a struct. This question checks whether a programmer can declare an array whose elements are bit-fields themselves, or whether bit-fields are only valid as members inside a struct. Understanding how bit-fields are defined and stored is essential for writing portable, correct C code. Given Data / Assumptions: C language, not C++. Standard bit-field syntax like unsigned int x:3; used only inside a struct. Need to decide if arr[i] can be declared directly as a bit-field element. Concept / Approach: In C, a bit-field is not a type on its own; it is a declarator that modifies a struct member. Therefore, bit-fields must be declared as members of a struct (or union). Arrays require an element type, but a bit-field does not constitute a standalone type, so an array of raw bit-fields is ill-formed. The correct approach is to put the bit-field inside a struct and then make an array of that struct. Step-by-Step Solution: 1) Recognize that `unsigned int:3` is not a type; it is a field width applied to a struct member. 2) Arrays require a complete element type such as int, char, or a struct type. 3) Because a bit-field is not a complete type, `unsigned int:3 arr[10];` is invalid. 4) Correct pattern: define a struct with a bit-field member, then declare an array of that struct. Example: `struct Flags { unsigned int f:3; }; struct Flags arr[10];` Verification / Alternative check: Try compiling `unsigned int:3 arr[10];`—a conforming compiler issues an error because the element lacks a proper type. The struct-array version compiles and works across compilers. Why Other Options Are Wrong: Option B: Suggests raw bit-field arrays; this is not allowed since a bit-field is not a standalone type. Option C: Width 1 does not change the rule; still not a type. Option D: C++ also requires bit-fields to be members; raw bit-field arrays are not valid there either. Option E: CHAR_BIT size is unrelated; portability does not make the construct valid. Common Pitfalls: Confusing a bit-field declaration with a type; assuming any bit width makes it a type; relying on non-portable extensions. Final Answer: No: declare a struct with bit-fields and make an array of that struct.

Question 18

In C, is the size of a union always exactly equal to the size of its longest (largest) member, or can alignment/padding make the union larger?

Accepted Answer

Introduction / Context: Unions overlay their members at the same memory location. This question probes understanding of how a union’s size is determined by the largest member and how alignment constraints may add padding, affecting the final size. Given Data / Assumptions: Standard C implementation with typical alignment rules. Union has members of possibly different sizes and alignment requirements. Concept / Approach: The C standard permits implementations to add padding so that any member can be accessed with proper alignment. Therefore, union size must be at least the size of its largest member, but may be rounded up to satisfy the strictest alignment requirement among its members. Step-by-Step Solution: 1) Identify the largest member size among all union members. 2) Determine the strictest alignment required by any member. 3) Compute the union size as a value not less than the largest member and possibly rounded up to the alignment boundary. 4) Conclude that equality is common but not guaranteed; alignment can increase size. Verification / Alternative check: On many systems, `sizeof(union)` equals `max(sizeof(member_i))`. On others, `sizeof(union)` may be larger to ensure that placing the union inside arrays or structs keeps members aligned. Why Other Options Are Wrong: Option B: Ignores alignment; not guaranteed. Option C: Unions do not sum sizes; that is for structs (and even then with padding). Option D: Bit-fields do not make a union smaller than its largest member. Option E: Optimization level does not change language alignment rules. Common Pitfalls: Assuming equality across all platforms; ignoring alignment when laying out data; relying on a specific `sizeof` in portable code. Final Answer: At least the largest member; may be larger due to alignment.

Question 19

In C, can a structure safely include a member that points to an object of the same structure type (a self-referential struct), and when is this useful?

Accepted Answer

Introduction / Context: Self-referential structures are a core technique in systems programming and data structures. This concept underlies linked lists, trees, and graphs implemented in C. Given Data / Assumptions: We are talking about a member that is a pointer to the same struct type. No attempt to embed a struct instance by value within itself. Concept / Approach: C allows a struct to contain a pointer to its own type because the pointer has a known, fixed size. What is not allowed is embedding an instance of the same struct by value (that would cause infinite regress and incomplete type sizing). A typical pattern is: struct Node { int data; struct Node *next; }; Step-by-Step Solution: 1) Declare the struct tag: `struct Node { ... };` 2) Inside, include a pointer to the same tag type: `struct Node *next;` 3) Use it to chain nodes: `head->next = new_node;` 4) Build lists, trees, or graphs using these pointers. Verification / Alternative check: Compilers accept such declarations and standard libraries and textbooks rely on them for classic data structures. Why Other Options Are Wrong: Option B: Incorrect; pointers to the same type are explicitly supported. Option C: A typedef is convenient but not required. Option D: Works in both C and C++. Option E: Volatile is unrelated to self-reference. Common Pitfalls: Attempting to embed a full struct of its own type by value; forgetting memory management, leading to leaks or cycles; confusion between tag names and typedef names. Final Answer: Yes—via a pointer member; this is how linked structures are built.

Question 20

C I/O and serialization: If we write the following struct instance with fwrite(), can we read it back with fread() and get the original data reliably across runs and machines?  struct emp {  char n;  int age; }; struct emp e = "CuriousTab", 15; / po…

Accepted Answer

Introduction / Context: This tests understanding of binary serialization in C. Writing a struct that contains pointers using fwrite() does not copy the objects those pointers reference. It only writes the immediate bytes of the struct itself, including raw pointer values that are meaningful only in the original process address space. Given Data / Assumptions: struct emp has a pointer member `char *n` and an int `age`. We call `fwrite(&e, sizeof(e), 1, fp)` to write the struct bytes. We later call `fread()` expecting to reconstruct the same logical data. Concept / Approach: Pointers store addresses, not the data they point to. `fwrite()` writes the pointer value (an address), which becomes meaningless when read back in another process or on another machine. To serialize correctly, either store the string content (e.g., write the characters and length) or redesign the struct to embed a fixed array, or use a proper serialization format. Step-by-Step Solution: 1) `sizeof(e)` covers the size of `char *` plus `int` and padding. 2) `fwrite()` outputs these raw bytes; the string literal data is not included. 3) On `fread()`, the pointer bytes are read back as an address that is invalid in the new process. 4) Correct pattern: store string contents explicitly (length + bytes) or use `char name[LEN];` in the struct and write that array. Verification / Alternative check: If you change process, restart, or move to a different machine or architecture, reading back the raw pointer yields undefined or useless addresses, demonstrating non-portability. Why Other Options Are Wrong: Option B: Misunderstands how fwrite works; it does not follow pointers. Option C/D: Optimization or text mode does not serialize pointed-to data. Option E: Member order does not solve the fundamental pointer issue. Common Pitfalls: Assuming fwrite serializes entire object graphs; ignoring endianness/ABI; forgetting to write string lengths; mixing text and binary I/O improperly. Final Answer: No—pointers are not serialized; write the pointed-to data explicitly or avoid pointers.

Structures, Unions, Enums Questions