CS354 Q2 — Memory & Addressing (Chunks 1–7)

Quiz-style practice matching the complete study reading. Terms = questions; definitions = answers with reasoning. Search [Chunk 1] through [Chunk 7] to study each chunk. Chunk 1 is starred. Chunk 7 allocator cards are labeled backup review. Original practice, not actual quiz questions.

[Chunk 1] Given int x = 12; int *p = &x;, what are x, p, and *p?

x is 12; p stores the address of x; *p is 12. The pointer value is an address, while dereferencing retrieves the pointed-to value.

[Chunk 1] If p stores the address of x, what does &p mean?

The address of the pointer variable p itself, not the address stored inside p.

[Chunk 1] Given int x = 4; int *p = &x; *p = 9;, what is x?

9. 9. Assigning through *p writes into x.

[Chunk 1] How do p = &y and *p = 7 differ?

p = &y changes which object p points to. *p = 7 changes the value of the object p currently points to.

[Chunk 1] Given int x = 8; int *p = &x; int **pp = &p;, what is **pp?

8. 8. First follow pp to p, then follow p to x.

[Chunk 1] Given int x; int *p = &x; int **pp = &p;, what are the types of pp, *pp, and **pp?

pp: int**; *pp: int*; **pp: int. Each dereference removes one pointer level.

[Chunk 1] In int *p, q;, which variables are pointers?

Only p is a pointer. q is an int. To declare both as pointers, write int *p, *q;.

[Chunk 1] A short* p points to 0x3000. Where is p + 4 if sizeof(short) is 2?

0x3008. Four elements × 2 bytes = 8 bytes.

[Chunk 1] An int* p points to 0x1000. Where is p + 3 if sizeof(int) is 4?

0x100C. Three elements × 4 bytes = 12 bytes.

[Chunk 1] For int a[10]; int *p = &a[2]; int *q = &a[7];, what is q - p?

5 elements, not 20 bytes. Pointer subtraction within the same array counts elements.

[Chunk 1] What does p + n use as its scale factor?

sizeof(*p), the size of the pointed-to type. Byte displacement = n × sizeof(*p).

[Chunk 1] Is dereferencing int *p = NULL valid? Explain.

No. NULL does not point to a valid object. Comparing p with NULL is valid; dereferencing it is not.

[Chunk 1] Why is dereferencing an uninitialized pointer unsafe?

Its stored address has not been established as the address of a live valid object.

[Chunk 1] C passes arguments by value. How can a pointer parameter change the caller’s variable?

The function receives a copy of the address. Dereferencing that copied address reaches the caller’s original object.

[Chunk 1] Trace: void f(int x, int *p){x=50; *p=60;} int a=1,b=2; f(a,&b); What are a and b?

a = 1; b = 60. x was a copied integer; *p accesses b.

[Chunk 1] A function assigns its pointer parameter p = &other. Does this reassign the caller’s pointer variable?

No. The pointer parameter is a copy. Reassigning it changes only that local copy.

[Chunk 1] Write an expression that reads x through int **pp when pp points to a pointer to x.

**pp

[Chunk 1] Explain what to draw for int x=3; int *p=&x; int **pp=&p;.

Three boxes: x holds 3; p holds x’s address and points to x; pp holds p’s address and points to p.

[Chunk 2] Rewrite a[3] using pointer arithmetic and dereferencing.

*(a + 3)

[Chunk 2] What does an array name usually decay to in an expression?

A pointer to its first element. The array itself is still an array object, not a pointer variable.

[Chunk 2] Given int a[6]; int *p=a;, what are sizeof(a) and sizeof(p) on course Linux (int 4, pointer 8)?

sizeof(a) = 24; sizeof(p) = 8. One measures the entire array; the other measures a pointer.

[Chunk 2] Why cannot sizeof(a) recover the original length inside void f(int a[])?

The array parameter is adjusted to a pointer, so sizeof(a) measures the pointer. Pass the length separately.

[Chunk 2] For int a[4][6] with 4-byte ints, find sizeof(a), sizeof(a[0]), and sizeof(a[0][0]).

96 bytes, 24 bytes, and 4 bytes respectively.

[Chunk 2] In row-major storage, what is the flat element index of row r, column c in C columns?

r * C + c. Multiply by sizeof(element) for the byte offset.

[Chunk 2] For int a[4][6], what is the byte offset of a[2][3] if ints are 4 bytes?

60 bytes: (2*6 + 3)*4.

[Chunk 2] For int a[3][4], how far do a + 1 and a[0] + 1 advance (int 4 bytes)?

a + 1 advances one 16-byte row. a[0] + 1 advances one 4-byte integer.

[Chunk 2] What type does int a[3][4] decay to?

A pointer to a row of 4 ints: int (*)[4]. It is not int**.

[Chunk 2] Why does a function indexing int a[][4] need the column dimension?

The column count determines the row stride, so the compiler can calculate a[r][c].

[Chunk 2] Can int a[7][5] be passed to a parameter declared int x[6][5]? Explain the dimensions.

Yes, in this ordinary array parameter form the first dimension adjusts away. The 5-column row type matches. Actual loops must still stay within the real array bounds.

[Chunk 2] Compare a rectangular int a[R][C] with an int** whose rows are separately allocated.

The rectangle stores all integers contiguously. int** leads to a table of row pointers; each row is a separate allocation and rows need not be adjacent.

[Chunk 2] How does board[r][c] access a separately allocated-row int**?

Read row pointer board[r], follow it, then index its c-th integer.

[Chunk 2] Why is an int** not interchangeable with a pointer to a contiguous rectangular row?

int** expects pointer entries in a table; a rectangular row pointer expects inline integer rows. Their storage interpretation differs.

[Chunk 2] A pointer table and 4 rows are separately malloc’d. How many frees, and in what order?

5 frees: free each row first, then free the pointer table.

[Chunk 2] A 4×6 integer board uses one flat malloc allocation. How many frees release it?

One free for that one allocation. Free counts depend on allocation structure, not the number of elements.

[Chunk 2] For ./tool 8 9 10, what is argc and what string is argv[2]?

argc = 4; argv[2] is "9". argv[0] is the program-name string.

[Chunk 2] For ./tool red blue green, what does *(argv + argc - 2) refer to?

argv[2], the string "blue". argc=4, so argc-2=2.

[Chunk 3] A local int *p points to malloc storage. Identify where p and *p’s object live.

p is typically on the stack; its target allocation is on the heap. Pointer storage and target storage are separate.

[Chunk 3] Classify int total=5; declared globally in the course memory model.

.data: nonzero-initialized global/static storage.

[Chunk 3] Classify an uninitialized global int counter; and state its initial value.

.bss; it starts at zero.

[Chunk 3] Classify a local static int saved=9; and explain its lifetime.

.data; the object persists for the program’s lifetime even though the name has local scope.

[Chunk 3] Where do machine instructions and string literals typically live?

Instructions: .text. String literals: .rodata.

[Chunk 3] Why is returning &x from a function with ordinary local int x invalid to use afterward?

x’s lifetime ends when the function returns. Returning its address does not extend its lifetime.

[Chunk 3] Distinguish scope from lifetime.

Scope is where a name can be used. Lifetime is how long the object exists. A local static has local scope but program-long lifetime.

[Chunk 3] Distinguish a memory leak from a dangling pointer.

Leak: allocated memory is not released and becomes unreachable. Dangling pointer: refers to an object whose lifetime ended, such as a freed allocation.

[Chunk 3] After free(p); p=NULL;, are other pointers to the old allocation safe?

No. Setting p to NULL changes only p; other aliases still dangle.

[Chunk 3] State course 64-bit Linux sizes of char, short, int, long, float, double, and pointer.

1, 2, 4, 8, 4, 8, and 8 bytes respectively, unless a problem specifies otherwise.

[Chunk 3] Do int* and char* have different sizes or different arithmetic scale factors?

Usually the same pointer size (8 bytes here), but different arithmetic scales: 4 bytes for int versus 1 for char.

[Chunk 3] Store 0xA1B2C3D4 at 0x6000 in little endian. Give bytes at increasing addresses.

0x6000:D4; 0x6001:C3; 0x6002:B2; 0x6003:A1. Least-significant byte is at the lowest address.

[Chunk 3] Store 0xA1B2C3D4 at 0x6000 in big endian. Give bytes at increasing addresses.

0x6000:A1; 0x6001:B2; 0x6002:C3; 0x6003:D4. Most-significant byte is at the lowest address.

[Chunk 3] Which byte address does a pointer to a multi-byte object identify?

The object’s lowest byte address, regardless of endian order.

[Chunk 3] Compare local char *p="cat"; with local char a[]="cat";. Which characters can be modified?

p points to a read-only string literal; modifying it is invalid. a is a writable local array containing c,a,t, and the zero terminator.

[Chunk 3] A global char a[80]="cat"; is used as a pointer. Which region does it address?

.data: the initialized global array itself. It is not the read-only literal target arrangement of char *p="cat";.

[Chunk 4] Rewrite p->score using dereference and member access.

(*p).score. The parentheses are needed because member access binds more tightly than unary *.

[Chunk 4] When do you use object.member versus pointer->member?

Use . for a struct/union object; use -> for a pointer to one.

[Chunk 4] Does typedef allocate storage or change a type’s memory layout?

No. It introduces a type alias. Declaring objects of that type allocates storage.

[Chunk 4] Layout char c; int i; short s; with sizes/alignments 1,4,2. Give offsets and total size.

c:0; padding:1-3; i:4-7; s:8-9; trailing padding:10-11. Total size 12, aligned to 4.

[Chunk 4] Layout short s; char c; int i; with sizes/alignments 2,1,4. Give offsets and size.

s:0-1; c:2; padding:3; i:4-7. Total size 8.

[Chunk 4] Explain the two alignment checks in a struct layout problem.

Align each member’s start to its required boundary; then round the entire struct size to its overall alignment so array elements remain aligned.

[Chunk 4] Why can reordering struct members change sizeof(struct)?

Different orders require different internal/trailing padding while preserving member alignment.

[Chunk 4] A struct has size 12. How many bytes does a pointer to it advance with p + 2?

24 bytes, including each struct’s padding.

[Chunk 4] Compare struct and union storage for int i and char c.

Struct members occupy distinct storage plus possible padding. Union members overlap at the same start; space is enough for the largest member with alignment rounding.

[Chunk 4] On the course model, why can reading a character view of a stored integer expose endianness?

It examines a byte of the integer’s memory representation. The first byte differs in little versus big endian.

[Chunk 4] Given int x=42; void *p=&x;, write an expression to read x via p.

*(int*)p. A void pointer needs an appropriate object-pointer type before dereferencing.

[Chunk 4] Does casting an address to another pointer type convert the underlying object?

No. A cast changes how the address is interpreted; it does not transform the stored object.

[Chunk 5] In P2, how do you locate row r, column c in the flat Cell array?

Index r*number_of_columns+c. Values are stored in row-major order.

[Chunk 5] What memory must be freed after transferring the int** P2 board into the flat Cell array?

Every separately allocated integer row, then the row-pointer table. The flat Cell allocation remains in use.

[Chunk 5] Which masks encode black, circle, and number in a P2 Cell byte?

Black:0x80; circle:0x40; number:0x1F. Number uses the low five bits.

[Chunk 5] Write an expression to extract a cell’s puzzle number without flags.

cell & 0x1F

[Chunk 5] Write a condition that tests whether cell is black.

(cell & 0x80) != 0

[Chunk 5] Write an update that sets the black flag while preserving the number.

cell |= 0x80; OR sets the bit without clearing the other bits.

[Chunk 5] Why is XOR with BLACK not a reliable operation for “mark black”?

XOR toggles the flag. An already-black cell would become unmarked instead of staying black.

[Chunk 5] Decode Cell 0x4D: puzzle number and flags.

Number13; circle set; black unset. 0x4D & 0x1F = 13.

[Chunk 5] Decode Cell 0x89: puzzle number and flags.

Number9; black set; circle unset. The full byte value is not the puzzle number.

[Chunk 5] State the three Hitori solution constraints.

No repeated surviving number in a row/column; no orthogonally adjacent black cells; all surviving cells remain orthogonally connected.

[Chunk 5] A cell is newly marked black. Which deduction applies to its neighbors, and why?

Circle deduction: orthogonal neighbors must survive because adjacent black cells are forbidden.

[Chunk 5] A cell is circled. What happens to other copies of its number in its row or column?

Blackout deduction: they must be blacked out to preserve uniqueness.

[Chunk 5] For 4,7,4 in adjacent row positions, what sandwich deduction follows? Explain.

Circle the middle 7. At least one 4 must be black; a black center would be adjacent to that black 4.

[Chunk 5] A row has an adjacent pair of 6s and another 6 elsewhere. What doublet deduction follows?

Black out the other 6. Exactly one adjacent 6 must survive: both black violates adjacency and both surviving violates uniqueness.

[Chunk 5] What is the reasoning behind a gate deduction?

If blacking out a cell disconnects surviving cells, it must remain available and be circled. This was optional extra-credit P2 logic.

[Chunk 5] Why do blackout() and circle() need already-marked early-return cases?

They can call each other recursively. Avoiding repeat work makes deduction chains terminate and prevents cycles; detect contradictory marks separately.

[Chunk 5] How many orthogonal neighbors does a board corner have, and what check prevents invalid access?

Two (for an ordinary board with at least two rows/columns). Check row/column bounds before visiting neighbors.

[Chunk 6] Which allocation function gives uninitialized contents, and which zero-initializes bytes?

malloc gives uninitialized storage; calloc zero-initializes count*size bytes.

[Chunk 6] Write the byte count needed to malloc an array of 6 ints.

6 * sizeof(int), not 6 alone.

[Chunk 6] What must you check before dereferencing a newly allocated pointer?

Check that allocation succeeded: the returned pointer is not NULL.

[Chunk 6] Why can realloc change the pointer address?

It may move the allocation to obtain enough space. Use its returned pointer after successful resizing.

[Chunk 6] If realloc fails, what happens to the original allocation?

It remains available. Preserve the original pointer until success; overwriting the only pointer with NULL loses access.

[Chunk 6] Does free(p) automatically set p and all aliases to NULL?

No. It releases the allocation; pointer variables retain their old values unless changed. Accessing the old allocation is invalid.

[Chunk 6] What are strlen("mouse") and the minimum bytes needed to store that string?

Length5; capacity6 bytes including the zero terminator.

[Chunk 6] What happens conceptually if a supposed C string lacks a terminator in accessible storage?

String functions can keep reading beyond the intended object, causing invalid access.

[Chunk 6] Does a == b compare C string contents when a and b are char pointers?

No. It compares addresses. Use strcmp for contents.

[Chunk 6] Interpret strcmp(a,b): zero, negative, and positive.

Zero: equal contents; negative: a sorts before b; positive: a sorts after b. Nonzero need not be exactly -1 or 1.

[Chunk 6] Joining strings of lengths 4 and 7 requires how much destination capacity?

At least12 bytes: 4+7+1 for the final terminator.

[Chunk 6] How do strcpy and strcat differ?

strcpy copies a string including its terminator. strcat appends to an existing terminated string. Both require sufficient writable destination space.

[Chunk 6] What does fopen return on failure, and what does mode "w" do?

Failure returns NULL. "w" opens for writing and creates or truncates the file.

[Chunk 6] What does fgets do about the terminator and a newline?

On success it zero-terminates the buffer; it may retain a read newline. One call may read only part of a long line.

[Chunk 6] Match stdin, stdout, stderr to uses and descriptor numbers.

stdin:input/0; stdout:normal output/1; stderr:error output/2.

[Chunk 6] Choose a GDB operation: stop at a specific line before investigating a bug.

Set a breakpoint at that line, then run or continue to reach it.

[Chunk 6] Choose a GDB operation: follow execution inside a called function.

Step into (step). Step over (next) instead executes the call without following its internal lines.

[Chunk 6] Choose a GDB operation: resume from a pause until the next breakpoint.

Continue.

[Chunk 6] Choose a GDB operation: inspect *p at the paused location.

Print the expression *p.