C++

Question 1

lvalue

Answer 1

a locatable (in memory) value.
a left hand value.
an “assignable” value.

http://eli.thegreenplace.net/2011/12/15/understanding-lvalues-and-rvalues-in-c-and-c

Question 2

rvalue

Answer 2

not an lvalue.
temporary object.
not addressable in memory

http://eli.thegreenplace.net/2011/12/15/understanding-lvalues-and-rvalues-in-c-and-c

Question 3

c++11 move semantics

Answer 3

allows rvalue -> lvalue assignment?

Question 4

Big 3

Answer 4

Relevent for class managing non trivial resources (ie heap data).
Consists of destructor, copy constructor and copy assignment operator (= overload)
If one is necessary to be defined, likely ALL are necessary due to complexities of class semantics.

Question 5

Big 5

Answer 5

Big3 + c++11 move semantics.

+move construtor and move assignment

Question 6

Copy and Swap Idiom

Answer 6

Relates to Big 3 and copy assignment.
Describes implementation of copy assignment.
Makes copy assignment simple and exception safe.
Requires definition of copy constructor, destructor and swap function.
1. create temp object (or in c++11 use passed in rvalue)
2. swap destination object and temp object data (pointer)
3. destroy temp object (c++11 rvalue destroyed automatically)

https://stackoverflow.com/questions/3279543/what-is-the-copy-and-swap-idiom

Question 7

Template Function Syntax

Answer 7

template
T Foo(Bar b){}
or
void Foo(T b){}

Question 8

braced initialization

Answer 8

int a{0};
preferred as its more widely compatible in different situations.
one caveat is that if you’re overloading constructors and one constructor takes std::initializer_list then that will be preferred to all other constructors - even though they may be more sensible.

Question 9

pimpl idiom to reduce build times (less header dependencies)

Answer 9

Basically moves all of class implementation to .cpp so header doesn't have to include details of members.
Therefore clients don't have to include those headers either.
Unique_ptr is preferred, but comes with gotcha's.

Question 10

smart pointers c++11/14

Answer 10

performance of unique_ptr almost matches raw.
prefer unique_ptr for single ownership.
shared_ptr is at least 2x as large as unique/raw and concurrent performance is a problem.
prefer shared_ptr for shared ownership.
prefer make_unique/make_shared to new.

Question 11

use constexpr when applicable

Answer 11

constexpr functions can produce compile-time results.

ex: size std::array based on function output at compile-time.

Question 12

use noexcept when applicable

Answer 12

improves ability for compiler to optimize.

Question 13

override

Answer 13

declare functions as override when thats what you’re doing.

avoids potential bugs where its actually not overriding but rather calling a separate function.

Question 14

prefer delete to private undefined functions

Answer 14

to disable copying, declare the copy constructor and delete: ex: Constructor() = delete;

Question 15

enum classes

Answer 15

use them!!!

no need for pre/appending name as they are in their own namespace.

Question 16

alias declarations

Answer 16

using foobar = std::vector;

can be used with templates more easily than typedef.

Question 17

nullptr

Answer 17

use it!!!

way! better than 0 or NULL which are basically hacks.

Question 18

auto

Answer 18

prefer, but has gotcha’s:
ex: auto bSomething = funcReturnsStdVectOfBools()[n];
in this unique case (amongst others) behavior is undefined.
The rvalue returned is of type std::vector::reference and the desired behavior is for this to be converted to a bool type not a &bool type - since a reference to the rvalue would result in undefined behavior. But this is just what auto bSomething will do.
The following is necessary:
ex: auto bSomething = static_castfunc…()[n];

Question 19

Template Class Syntax

Answer 19

template
class Foo
{};

Question 20

TDD in C++

Answer 20

1. write test (won’t compile because no source)
2. write source stubs (test now compiles, but fails)
3. fill in source till test passes
4. refactor so code is best possible form (and passes)

http://www.drdobbs.com/cpp/test-driven-development-in-cc/184401572

Question 21

Virtual Destructors

Answer 21

When a derived class is deleted by its base pointer a base virtual destructor is required to avoid undefined behavior.
Abstract interfaces require it.

Question 22

strace

Answer 22

trace system calls

Question 23

valgrind

Answer 23

heap memory analyzer

Question 24

gprof, oprofile, perf

Answer 24

performance analyzers

Question 25

gcov

Answer 25

code coverage analyzer

Question 26

perf

Answer 26

observe, collect stats on system.

CPU, I/O, software, scheduling.

Question 27

random numbers C/C++

Answer 27

C:
#include 
#include 
srand(time(NULL)); // seed, once per thread
rand(); // returns random number
C++:
#include 
#include 
srand((unsigned)time(0)); // seed, once per thread
rand(); // returns random number

Question 28

C unions

Answer 28

ex:
union Data {
   int i;
   float f;
   char str[20];
} data;
Aliasing single memory as different types.
Purpose is to time share memory with different types.

Question 29

C++ &&

Answer 29

rvalue reference.

overloaded construct/copy operators to use rvalues.

Question 30

C measuring time (clock_t)

Answer 30

#include 
clock_t start = clock(), diff;
doSomething();
diff = clock() - start;
unsigned ms = (diff * 1000)/CLOCKS_PER_SEC;

Question 31

C/C++ main signature

Answer 31

int main(int argc, char** argv)
int main(int argc, char* argv[])
int main(void)

Question 32

C struct packing

Answer 32

struct variables will align to memory so order/group them to optimally fill memory words (8bytes on 64bit)

64bit system (pointers are 8bytes):
struct foo {
int b; //4 bytes (will consume 8 bytes to align)
void* p; // 8 bytes
};
values will need to align in memory.

Question 33

const char*
char* const
const char* const

Answer 33

point to const char
const pointer to char
const pointer to const char

Question 34

space float vs. double

Answer 34

double takes 2x the space as it has double accuracy

typically float=4bytes, double=8

Question 35

C I/O

Answer 35

#include 
#include 
printf("%s, %c, %p, %u, %d\n", string, char, pointer, unsigned, int);

Question 36

C++ I/O

Answer 36

#include 
#include 
cout << "hello" << a << f << endl;
string input;
getline(cin, input);
cout << intput;

Question 37

C heap allocation/deallocate

Answer 37

struct node* head = malloc(sizeof(struct node));

free(head);

Question 38

C++ heap allocation/deallocation

Answer 38

struct node* head = new struct node();
delete head;
int array[] = new int[10];
delete [] array;

Question 39

Virtual Template Function?

Answer 39

Virtual methods mean a run-time vtable lookup.
Templates are resolved at compile-time.
Not compatible.