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C++ 11
Language enhancements and additions
Telerik Software Academy
Learning & Development Team
http://academy.telerik.com
Table of Contents (1)
1.
Runtime performance enhancements
 Rvalue references and move constructors
 Generalized constant expressions
2.
Usability enhancements






Initializer lists
Type inference
Range based for loop
Lambda functions and expressions
Null pointer constant
Right angle bracket
2
Table of Contents (2)
3.
Standard Template Library
 Tuple types
 Hash tables
 Extensible random number facility
4.
Algorithms
 Non-modifying / modifying sequence
 Sorting, minmax, heaps
Rvalue references
T&& and move constructor
Rvalues
 Lvalues
(references)
 Lie on the left side of assignments
 Identified by T&
 Rvalues (temporaries)
 Lie on the right side of assignments
 Identified by T&&
 Make move semantics possible
Rvalues
 Move constructors
on STL containers:
 Given a really big string (1GB)
string str(1<<30);
 Copies the big string
 Slow and allocates another 1GB of memory
string str_copied = str;
 Moves the contents of str to str_moved
 Fast and doesn't allocate another 1GB of memory
 str will be an empty string after the assignment
string str_moved = move(str);
6
Rvalues
 Move semantics on STL containers:
string append_char(string str, char ch) {
str += ch;
return move(str);
}
// Really big string (1GB)
string str(1<<30);
string str2 = append_char(move(str), '5');
7
Constant expressions
constexpr keyword
Constexpr

Allows constant expressions to be functions
// Array size must be a compile time constant
int A[5+10*23];
// constexpr keyword guarantees that
// a function is a compile time constant
constexpr int square(int x) {
return x*x;
}
int B[square(10)];

Restrictions (more relaxed in C++ 14)
 Function must be non-void
 Variables can not be declared
 Types can not be defined
 Only one statement allowed (return value)
Initializer lists
Initializing arrays, containers and other structures
Initializer lists
 Initializer
list ({value, value, … })
 Type initializer_list can be cast to:
 STL containers
 Pairs and tuples
 Custom structures
 Can be nested
 "=" can be omitted ( uniform initialization )
Initializer lists
Examples:
int array[] = {1, 3, 2, 5, 7}; // from C
vector<int> v = {1, 3, 2, 5, 7};
v = {1, 2, 3};
set<int> s = {1, 3, 2, 5, 7};
pair<int, int> SumAndDif(int a, int b) {
return {a+b, a-b};
}
map<string, int> Map = {
{"banana", 3},
{"apple", 7},
{"cherry", -5}
};
12
Initializer lists
Examples:
struct rgb {
double red;
double green;
double blue;
}
// Can be used on custom structures
rgb color = {1.0, 0.5, 0.0};
// Can be nested
vector<rgb> colors = {
{0, 0, 0},
{1, 1, 1},
{0.5, 0, 1},
{0.2, 0.8, 0.4}
};
13
Type inference
auto, decltype
Type inference
 Auto (auto
variable = value)
 Deduces type for variable from value
 Does not deduce const types
 Does not deduce reference (&) types
 Decltype (declype(expression))
 This is the type of the expression
 Can deduce const types
 Can deduce reference types
15
Type inference
 Examples:
int a0;
auto a1
auto a2
auto a3
auto a4
// int (apparently)
= a0; // int
= 7; // int
= 7-a0*(13+a1); // int
= 2ll; // long long
const char c0 = 'x'; // const char (apparently)
auto c1 = c0; // char (non-const)
const auto c2 = c0; // const char
char &r0 = c1; // char& (apparently)
auto r1 = r0; // char (non-reference)
auto &r2 = r0; // char&
int *p0 = &a0; // int* (apparently)
auto p1 = p0; // int*
Type inference
 Useful when working with iterators
map<string, int> Map;
for (map<string, int>::iterator it = Map.begin();
it != Map.end(); ++it) {
cout<< it->first <<" -> "<< it->second <<'\n';
}
// becomes
for (auto it = Map.begin(); it != Map.end(); ++it) {
cout<< it->first <<" -> "<< it->second <<'\n';
}
Type inference
 Examples:
int a;
// decltype(a) is int
// decltype((a)) is int&, because (a) is an lvalue
// decltype(0) is int, because 0 is an rvalue
const vector<int> v(1);
// decltype(v[0]) is const int&
Range based loops
Iterating over arrays and containers
Range based loops
 Iterating over range of elements
 C style arrays
 STL containers
 Initializer lists
 Any type with defined begin() and end() functions
20
Range based loops
 Accessing all elements
int A[10] = {1, 5, 9, 2, 4, 0, 2, 2, 7, 9};
for(int x:A) {
cout<<x<<'\n';
}
 Modifying all
elements
int A[10] = {1, 5, 9, 2, 4, 0, 2, 2, 7, 9};
for(int x:A) { // Copies each element in x
x *= 2; // A is not modified
}
for(int &x:A) { // Using reference
x *= 2; // A is modified
}
Range based loops
 Can be used on STL containers
vector<string> = {"Pencil", "Knife", "Ball"};
for(string &x:A) {
reverse(x);
}
 Combining with auto
map<string, int> Map;
for (pair<string, int> &x:Map) {
cout<<x.first<<" -> "<<x.second<<'\n';
}
// becomes
for (auto &x:Map) {
cout<<x.first<<" -> "<<x.second<<'\n';
}
Lambda functions
Definition and usage
Lambda functions
 [](int
x,int y) { return x+y; }
 Return type is decltype(x+y)
 Variable
capture
 []
 [variable]
 [&variable]
 [&]
 [=]
24
Lambda functions
Examples:
vector<int> v;
sort(v.begin(), v.end(), [](int x, int y) {
return abs(x) < abs(y);
});
int n; cin >> n;
sort(v.begin(), v.end(), [&n](int x, int y) {
return x%n < y%n;
});
Null pointer constant
nullptr constant
Null pointer constant
 nullptr – Constant
of type nullptr_t
 Can be cast to any pointer type
 Can not be cast to integer types
 Can be cast to bool ( it's false )
void f(int);
void f(char*);
// NULL is defined as 0 which is int
f(NULL); // calls f(int) – Wrong
f(nullptr); // calls f(char*) – Correct
27
Space Between
Right-angle brackets

Nested template declarations
 Before C++ 11 ">>" is always defined as right shift
C++ 03 and before
vector<vector<int> > items
C++ 11
vector<vector<int>> items
Space Between
Right-angle brackets

Nested template declarations
 Before C++ 11 ">>" is always defined as right shift
C++ 03 and before
vector<vector<int> > items;
Space required
before C++ 11
C++ 11
vector<vector<int>> items;
Space not required
in C++ 11
Tuples
Creating and using tuples
Tuple
 Tuple (#include
<tuple>)
 Creating tuples
 tuple<type1, type2, ...> t;
 tuple<type1, type2, ...> t(value1, value2, …);
 tuple<type1, type2, ...> t{value1, value2, …};
 make_tuple(value1, value2, …);
 Accessing tuple elements (get)
 Unpacking tuples (tie, ignore)
 Concatenating tuples (tuple_cat)
31
Tuples
Examples:
tuple<int, string, bool> tup(42, "hamster", true);
cout << get<0>(tup); // cout's 42
cin >> get<1>(tmp); // cin's a string
get<2>(tmp) = false;
// Unpacking the tuple in
// num and str, ignoring the Boolean
// tie creates a tuple of references
int num;
string str;
tie(num, str, ignore) = tup;
Tuples
Examples:
tuple<int, string, bool> tup(42, "hamster", true);
int n = 17;
auto tup2 = tuple_cat(tup, make_tuple(3.5), tup, tie(n));
// tup2 is of type tuple<int, string, bool, double,
int, string, double, int&>
n = 19; // last element in tup2 is reference to n
// (42, "hamster", true, 3.5, 42, "hamster", 19)
Hash tables
Unordered_(multi)set, unordered_(multi)map
Hash tables
 Unordered_(multi)set, unordered_(multi)map
 Same as (multi)set and (multi)map
 but unordered
 Key must have defined Hash function instead of
Compare
 Extracting elements one by one:
 Yields the elements in some order
Hash tables

Unordered_(multi)sets (#include<unordered_set>)
 unordered_set<Key,
Hash = hash<Key>,
Alloc = new>

Unordered_(multi)maps (#include<unordered_map>)
 unordered_map<Key, Value
Hash = hash<Key>,
Alloc = new>

Constant average times for operations
36
Random number facility
Random number generators and distributions
Random numbers
 Non-deterministic numbers
 random_device
 Random number engines
 Predefined generators
 Engine adaptors
 Distributions
 Uniform
 Normal
 Others
38
Random number generators
 linear_congruential_engine
 minstd_rand
 minstd_rand0
 mersenne_twister_engine
 mt19937
 mt19937_64
 subtract_with_carry_engine
 ranlux24_base
 ranlux48_base
Random number generators
adaptors
 discard_block_engine
 ranlux24
 ranlux48
 independent_bits_engine
 shuffle_order_engine
 knuth_b
Random number generators
Examples:
#include <random>
using namespace std;
int main() {
random_device rd;
// get a random number
cout << rd() << '\n';
mt19937 gen(seed); // seed can be rd()
// get a pseudo-random number
cout << gen() << '\n';
}
Random number distributions
 Uniform distributions
 uniform_int_distribution
 uniform_real_distribution
 generate_canonical
 Normal distributions
 normal_distribution
 Others
 Others
Random number distributions
Examples:
mt19937 gen{random_device{}()}; // generator
uniform_int_distribution<int> dice(1, 6);
// Gives number from 1 to 6 with equal probability
dice(gen);
uniform_real_distribution<double> reals(0.0, 10.0);
// Evenly distributed real numbers from 0 to 10
reals(gen);
normal_distribution<double> gauss(42, 5);
// Numbers close to 42 will be most probable
// 5 is standard deviation
gauss(gen);
Algorithms
New algorithms in <algorithm>
Algorithms

Non-modifying sequence operations
 all_of(first, last, predicate)
 any_of(first, last, predicate)
 none_of(first, last, predicate)

Modifying sequence operations
 move(first, last, d_first)
 move_backwards(first, last, d_last)
 shuffle(begin, end, generator)
 Uses the new random number functionality
 Replaces random_shuffle
45
Algorithms

Sorting operations
 is_sorted(begin, end)
 is_sorted_until(begin, end)

Min/max operations
 minmax(a, b)
 minmax_element(begin, end)
 is_permutation(first1, last1,
first2, last2)

Heap operations
 is_heap(begin, end)
 is_heap_until(begin, end)
46
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