C++ Pointers

Front 1

int i = 2;
int j = ++i;
j++;
cout << i << " ";
cout << j << " ";
cout << (&i == &j) << endl;

Back 1

3 4 false

Front 2

int i = 2;
int& j = ++i;
j++;
cout << i << " ";
cout << j << " ";
cout << (&i == &j) << endl;

Back 2

4 4 true

Front 3

const int a[] = {2,3,4}

creates an array where in C++

Back 3

stack

Front 4

final int[] a = {2,3,4}

creates what on where in Java

Back 4

reference, heap

Front 5

final int[] a = {2,3,4}

changing possible?

Back 5

reference to array in Java is immutable, but array contents are mutable

Front 6

const int a[] = {2,3,4}

changing possible?

Back 6

no

Front 7

int i = 2
int& j = ++i

explain

Back 7

reference ties j to i (so changing j changes i)

Front 8

Object's equals() compares ..., not ...

Back 8

references, not contents

Front 9

C++ const vars must be ... when declared

Back 9

initialized

Front 10

type*, e.g. int*

means

Back 10

reads as pointer to an int and denotes the address of the var which is of type int

Front 11

*variable, e.g. *p

Back 11

p is an int* and reads "value at address". So ++p means incrementing the pointer (or address), whereas ++*p means incrementing the value at the address (stored by p) by 1.

Front 12

type&, e.g. int& j = ++i

Back 12

this should be read as the "address of an int stored in j has been assigned the incremented value of i", which means i and j are now tied forever so whenever i changes, j changes to match it and vice versa. This also means j is another name for i and cannot be assigned to another value later (I think) and you also can't increment j like ++*j since j isn't an address. It'd the equivalent of saying ++*i which doesn't make sense. If you print both of i and j's address in memory, they both have the same address.

Front 13

variable&, e.g. int* p = &j,

Back 13

says that the "address of" j is stored in a pointer to an int and that pointer is called p in this case.

Front 14

void g(int* p){ ++p;}

int main () {
int j = 3;
g(&j);
cout << j }

prints what

Back 14

3

Front 15

void g(int* p){
++*p;
cout << *p
}

int main () {
int j = 3;
g(&j);
cout << j

}

prints what, explain

Back 15

3
4
(p == &j) = true (even if p dies after going back to main)

Front 16

void g(int& p){ ++p;}

int main () {
int j = 4;
g(j);
cout << j }

prints what. explain

Back 16

5, p is another name for j (big picture)

Front 17

void h(int& r) is a method whose argument demands a ... that cannot be ...

Back 17

l-value that cannot be 0 since it's a null address

Front 18

& should be read as ...

Back 18

address-of operator

Front 19

* should be read as ...

Back 19

value-at-address operator

Front 20

int i = 2;
++-i;

explain (C++)

Back 20

++-i will throw an error bc C++ requires an l-value as increment operand

Front 21

int i = 2
++++i

explain (C++)

Back 21

++++i is allowed bc C++ requires an l-value as increment operand

Front 22

int a[] = {2, 3, 4};
assert(a[1] == 3); // array index
++a[1];
a[1] is

Back 22

4

Front 23

const int a[] = {2,3,4};
const int b[] = a;
cout << "a address: " << &a << "\nb address: " << &b << endl;

Back 23

runtime error: initializer fails to determine size of 'b' not bc it's const though, but bc int[] needs to be initialized w/specific size

Front 24

int a[] = {2,3,4};
int b[] = a;
cout << "a address: " << &a << "\nb address: " << &b << endl;

Back 24

runtime error: initializer fails to determine size of 'b' bc int[] needs to be initialized w/specific size

Front 25

int j = 2;
int* p = &j;
++*p;
cout << j << endl;

Back 25

3

Front 26

int j = 2;
int* p = &j;
++*p;
cout << *p << endl;

Back 26

3

Front 27

int j = 2;
int* p = &j;
++*p;
cout << (p == &j) << endl;

Back 27

true

Front 28

int j = 2;
int* p = &j;
++*p;
cout << (*p == &j) << endl;

Back 28

ISO C++ forbids comparison between pointer and integer [-fpermissive]

Front 29

final int[] a = {2, 3, 4};
final int[] b = a;
print (a == b);
++b[1];
print a[1]
print b[1]
print (a == b)

Back 29

JAVA
true
4
4
true

Front 30

final int[] a = {2, 3, 4};
final int[] b = a.clone();
print (a == b);
++b[1];
print a[1]
print b[1]
print (a == b)

Back 30

JAVA
false
3
4
false

Front 31

int k = 2;
int& r = k;
++r;
cout << r << endl;
cout << k << endl;

Back 31

3
3

Front 32

int i = 2;
int* p = &i;
int*& r = p;
++*r;
cout << i

Back 32

3

Front 33

int i = 2;
int* p = &i;
int*& r = p;
++*r;
cout << *p

Back 33

3

Front 34

int i = 2;
int* p = &i;
int*& r = p;
++*r;
cout << *r

Back 34

3

Front 35

int i = 2;
int* p = &i;
int*& r = p;
++*r;
cout << (&r == &p)

Back 35

true

Front 36

int a[] = {2,3,4};
int* p = &a[0];
(*p == a[0])

Back 36

true

Front 37

int a[] = {2,3,4};
int* p = &a[0];
(p == a)

Back 37

true

Front 38

int a[] = {2,3,4};
int* p = &a;
(*p == a[0])

Back 38

error: cannot convert ‘int (*)[3]’ to ‘int*’ in initialization

Front 39

int a[] = {2,3,4}
sizeof(a) with respect to sizeof(&a[0])

Back 39

not equal

Front 40

int a[] = {2,3,4}
sizeof(a)

Back 40

12

Front 41

int a[] = {2,3,4}
sizeof(a[1])

Back 41

8

Front 42

int a[] = {2,3,4}
++a

Back 42

error: lvalue required as left operand of assignment

Front 43

int a[] = {2,3,4}
++*(a+1)

Back 43

same as ++a[1]

Front 44

int a[] = {2,3,4}
a[3] == 0

Back 44

undefined

Front 45

int a[] = {2,3,4}
int* b = a
a == b

Back 45

true

Front 46

int a[] = {2,3,4}
int* b = a
sizeof(a)

Back 46

12

Front 47

int a[] = {2,3,4}
int* b = a
sizeof(b)

Back 47

8

Front 48

int a[] = {2,3,4}
int* b = a
++b[1]

Back 48

4

Front 49

int a[] = {2,3,4}
int* b = a
++b[1]
a[1]

Back 49

4

Front 50

int a[] = {2,3,4}
int* b = a
b[1]

Back 50

3

Front 51

int a[] = {2,3,4}
int* b = a
&a is the same as what

Back 51

&b[0] and &a[0]

Front 52

int a[] = {2,3,4}
int* b = a
*b

Back 52

2

Front 53

int a[] = {2,3,4}
int* b = a
*b[0]

Back 53

error: invalid type argument of unary '*' (have 'int')

Front 54

int a[] = {2,3,4}
int* b = a
&b is the same as what

Back 54

none of the addresses. the pointer's address is where the pointer lives so it should not be the same as anything in the array. &b[0] does contain the same as &a[0] though

Front 55

bool equal_1 (int* b, int* e, int* c) {
while (b != e) {
if (*b != *c)
return false;
++b;
++c;}
return true;}

template <typename II1, typename II2>
bool equal_2 (II1 b, II1 e, II2 c) {
while (b != e) {
if (*b != *c)
return false;
++b;
++c;}
return true;}

main() {
int a[] = {2, 3, 4};
int b[] = {2, 3, 4, 5};

assert(equal (a, a + 3, b));
assert(equal_1(a, a + 3, b));
assert(equal_2(a, a + 3, b));

list<int> x(a, a + 3);
list<int> y(b, b + 4);

assert(equal (x.begin(), x.end(), y.begin()));
// assert(equal_1(x.begin(), x.end(), y.begin()));
assert(equal_2(x.begin(), x.end(), y.begin()));

}

Back 55

// error: cannot convert ‘std::_List_iterator<int>’ to ‘int*’ for argument ‘1’ to ‘bool equal_1(int*, int*, int*)’

Front 56

java
Integer x = new Integer(2);
Integer y = new Integer(2);
x == y

Back 56

false

Front 57

java
Integer x = new Integer(2);
Integer y = new Integer(2);
x.intValue() == y.intValue();

Back 57

true

Front 58

java
Integer x = new Integer(2);
Integer y = new Integer(2);
++x;
++y;
x == y;

Back 58

true

Front 59

java
Integer x = 128;
Integer y = 128;
x == y;

Back 59

false, cache: [-128, 127]

Front 60

java
Long x = 128L;
Long y = 128L;
x == y

Back 60

false

Front 61

java
Integer x = 127;
Integer y = 127;
x == y;

Back 61

true, cache: [-128, 127]

Front 62

java
Long x = 127L;
Long y = 127L;
x == y

Back 62

true

Front 63

java
Long x = (long) 2
compiles?

Back 63

yes

Front 64

java
Long x = 2
compiles?

Back 64

no

Front 65

java
long x = 2
compiles?

Back 65

yes

Front 66

java
long j = 2;
// Integer x = j; // doesn't compile
Integer x = (Integer) j
compiles?

Back 66

no, error: inconvertible types

Front 67

java
long j = 2;
// Integer x = j; // doesn't compile
Integer x = (int) j
compiles?

Back 67

yes

Front 68

java
int[] a = {2, 3, 4};
Integer[] b = a
compiles?

Back 68

no, error: incompatible types

Front 69

java
int[] a = {2,3,4}
Integer[] b = {2,3,4}
compiles?

Back 69

yes

Front 70

java
String s = "abc"
String t = "abc"
s == t

Back 70

true, literal Strings are cached

Front 71

java
String s = "abc"
String t = "ab" + "c"
s == t

Back 71

true

Front 72

java
String s = "abc"
String u = "ab"
String v = "c"
String t = u + v
s == t

Back 72

no, t doesn't have literal String

Front 73

java
String s = "abc"
String u = "ab"
String v = "c"
String t = u + v
s.equals(t)

Back 73

true

Front 74

unary ‘&’ operand requires

Back 74

l-value

Front 75

c++
const char* a = "abc"
char** pointerofa = &a

Back 75

error: invalid conversion from const char** to char**

Front 76

c++
const char* a = "abc"
char* pointerofa = &a

Back 76

error: cannot convert const char** to char* in initialization

Front 77

c++
const char* a = "abc"
char* pointerofa = a

Back 77

error: invalid conversion from const char* to char*

Front 78

c++
const char* a = "abc"
char* pointerofa = *a

Back 78

error: invalid conversion from char to char*. recall *a gives you the char 'a' from the string "abc" so you're trying to make it a pointer to a char

Front 79

c++
const char* a = "abc"
char pointerofa = *a

Back 79

ok, same as
char pointerofa = 'a'

Front 80

c++
const char* a = "abc"
const char* b = "abc"
&a == &b

Back 80

false

Front 81

c++
const char* a = "abc"
const char* b = "abc"
a == b

Back 81

true as contents of a and b are equal

Front 82

c++
const char* a = "abc"
const char* b = "abc"
*a == *b

Back 82

true as *a and *b is the char 'a'

Front 83

c++
const char* a = "abc"
a = "def"
compiles?

Back 83

yes, the address of the new a is the same as when it was declared, but content is different

Front 84

c++
char[]* a = "abc"

Back 84

error: expected unqualified-id before ‘[’ token

Front 85

c++
const char* a = "abc"
&(*a)

Back 85

abc
why?

Front 86

c++
const char* a = "abc"
char p = *a
&(p)

Back 86

a
why

Front 87

c++
const char* a = "abc"
*a

Back 87

letter a

Front 88

c++
const char* a = "abc"
char p = *a
p

Back 88

letter a

Front 89

C++
const char* a = "abc"
const char* addressOfLetterA = &(*a)

Back 89

a is forever the pointer of "abc" with const char * so if you want to store the address of "abc" somewhere else, use const char*.
addressOfLetterA and a will have the same memory address

Front 90

char* salutation = "Hello world!";

Back 90

/* 'salutation' addresses immutable memory */ If you need to change the content, use:
char salutation[] = "Hello world!";

Front 91

& requires what kind of value?

Back 91

l-value

Front 92

const char a[] = "abc";
const char b[] = "abc";
cout << *a << endl;
cout << *b << endl;

Back 92

a
a

Front 93

const char a[] = "abc";
const char b[] = "abc";
cout << &a << endl;
cout << &b << endl;

Back 93

a and b have different addresses

Front 94

c++
char* a = "abc"
char* r = &(*a)
do a and r's address match?

Back 94

no

Front 95

c++
const char* a = "abc"
const char* r = &(*a)
do a and r's address match?

Back 95

yes

Front 96

char a[] = "abc";
char b[] = "abc";
cout << &a << endl;
cout << &b << endl;

Back 96

a and b have different addresses

Front 97

java
int[] a = {2, 3, 4};
a.equals(new int[]{2, 4, 4});

Back 97

false

Front 98

java
int[] a = {2, 3, 4};
Arrays.equals( a, new int[]{2, 4, 4} );

Back 98

true

Front 99

int a[] = {2,3,4};
a == &a

Back 99

error

Front 100

int a[] = {2,3,4};
a == &a[0]

Back 100

true

Front 101

size_t s = 10;
int a[s] = {2,3,4};
cout << a[4]

Back 101

error: variable-sized object ‘a’ may not be initialized

Front 102

int a[10] = {2,3,4};
cout << a[4]

Back 102

0

Front 103

int a[] = {2, 3, 4};
int* const b = a;
a == b

Back 103

true

Front 104

int a[] = {2, 3, 4};
const size_t s = sizeof(a) / sizeof(a[0]);
int b[s];
copy(a, a + s, b);
a == b

Back 104

false

Front 105

int a[] = {2, 3, 4};
const size_t s = sizeof(a) / sizeof(a[0]);
int b[s];
copy(a, a + s, b);
equal(a, a + s, b)

Back 105

true

Front 106

int a[] = {2, 3, 4};
const size_t s = sizeof(a) / sizeof(a[0]);
int b[s];
copy(a, a + s, b);
a[0] == b[0]

Back 106

true bc content is the same//used to be false.
a == &a[0] is also true even if
a == b is false.
&a[0] != &b[0]

Front 107

int a[] = {2, 3, 4};
const size_t s = sizeof(a) / sizeof(a[0]);
int b[s];
copy(a, a + s, b);
a[1] == b[1]

Back 107

true bc content is the same. addresses of a[1] and [b1] are not the same

Front 108

int a[] = {2, 3, 4};
const size_t s = sizeof(a) / sizeof(a[0]);
int b[s];
copy(a, a + s, b);
++a[1];
a[1] == b[1]

Back 108

false bc content changed

Front 109

int a[] = {2, 3, 4};
int b[] = {5, 6, 7};
b = a;

Back 109

error: invalid array assignment

Front 110

difference between c string and c++ string

Back 110

C string is a char array whose last element is '\0'.
The == operation checks if the references are the same. You need strcmp for content.
C++ string is an object. The == operator checks the content.

Front 111

const ptrdiff_t s = 10;
const int v = 2;
int* const a = new int[s]; //initialized w/0
fill(a, a + s, v);
assert(count(a, a + s, v) == s);
assert(a[1] == v);
a == &a[0]
// ++a//error: increment of read-only variable

Back 111

true, before and after fill operation, addresses of a and a[0] are the same (const)

Front 112

const size_t s = 10;
const int v = 2;
int* const a = new int[s];
fill(a, a + s, v);
int* const b = a;
assert(&a[1] == &b[1]);
int* const c = a; //ok
b = c;

Back 112

error: assignment of read-only variable 'b'

Front 113

const size_t s = 10;
const int v = 2;
int* const a = new int[s];
fill(a, a + s, v);
int* b = new int[s];
fill(b, b + s, v);
// b = a; // memory leak
copy(a, a + s, b);

Back 113

copy overwrites, i guess? if you do "b = a" that creates a new int[]?

Front 114

allocator<int> x;
const ptrdiff_t s = 3;
const int v = 2;
int* const a = x.allocate(s); //*a is 0
int* b = a;
int* e = a + s;
while (b != e) {
x.construct(b, v); //*b is v
++b;}
assert(count(a, a + s, v) == s);
b = a; //assigning the beginning of a to b
while (b != e) {
--e;
x.destroy(e);}
x.deallocate(a, s);

Back 114

int* b = a where a is * to int/array can result in b being used as a *

Front 115

struct A {
int i;
void f () {
}
};
struct B : A {
int j;
void f () {
}
};

A a[] = {B(), B(), B()}; // slice
a[1].f(); //which struct's f() gets called

Back 115

A::f();

Front 116

A* const a = new B[10]; // dangerous
a[0].f(); // A::f()
// a[1].f(); // undefined
// delete [] a; // undefined
static_cast<B*>(a)[1].f(); // B::f()
delete [] static_cast<B*>(a); // ~B::B() and ~A::A()

Back 116

struct A {int i; void f () {}};
struct B : A {int j; void f () {}};

Front 117

const size_t s = 10;
const int v = 2;
vector<int> x(s, v);
assert(x.size() == s);
assert(x[0] == v);
vector<int> y(x);
assert(x.size() == y.size());
assert( x[1] == y[1]);
assert(&x[1] != &y[1]);
vector<int> z(2 * s, v);
x = z;
assert(x.size() == z.size());
assert( x[1] == z[1]);
assert(&x[1] != &z[1]);

Back 117

content is the same. addresses are not

Front 118

struct A {
A () {cout << "A() ";} // default constructor
A (int) {cout << "A(int) ";} // int constructor
A (const A&) {cout << "A(A) ";} // copy constructor
~A () {cout << "~A() ";} // destructor
A& operator = (const A&) {cout << "=(A) "; return *this;}}; // copy assignment operator

int main () {
{
A a[5] = {2, 3, 4};
cout << endl;
}
cout << endl;

Back 118

A(int) A(int) A(int) A() A()
~A() ~A() ~A() ~A() ~A()

Front 119

struct A {
A () {cout << "A() ";} // default constructor
A (int) {cout << "A(int) ";} // int constructor
A (const A&) {cout << "A(A) ";} // copy constructor
~A () {cout << "~A() ";} // destructor
A& operator = (const A&) {cout << "=(A) "; return *this;}}; // copy assignment operator

int main () {
{
A x;
cout << endl;

A* a = new A[5];
cout << endl;

fill(a, a + 5, x);
cout << endl;

delete [] a;
cout << endl;
}
cout << endl;

return 0;}

Back 119

A()
A() A() A() A() A()
=(A) =(A) =(A) =(A) =(A)
~A() ~A() ~A() ~A() ~A()
~A()

Front 120

public static void main (String[] args) {
{
final long[] a = {2, 3, 4};
arraycopy(a, 0, a, 1, 2);
assert Arrays.equals(a, new long[]{2, 2, 3});
}

{
final long[] a = {2, 3, 4};
arraycopy(a, 1, a, 0, 2);
assert Arrays.equals(a, new long[]{3, 4, 4});
}}}

public static void arraycopy (long[] a, int i, long[] b, int j, int s) {

Back 120

public static void arraycopy (long[] a, int i, long[] b, int j, int s) {
if (j < i) {
int n = 0;
while (n != s) {
b[j + n] = a[i + n];
++n;}}
else {
int n = s;
while (n != 0) {
--n;
b[j + n] = a[i + n];}}}

Front 121

{
int i = 2;
int* p = &i;
int** pp = &p;
int** qq = pp;
++**qq;
cout << i << " ";
++qq;
cout << (pp == &p) << endl;
}

{
int i = 2;
int* p = &i;
int** pp = &p;
int**& qq = pp;
++**qq;
cout << i << " ";
++qq;
cout << (pp == &p) << endl;
}

Back 121

3 true
3 false