Based on Morten Nobel-Jørgensen's C++ Reference. Edited by Dov Kruger
A concise overview of basic, modern C++ (C++14).
Any line with a preprocessor directive (starting with #) is executed before the compiler, changing the source code before the compiler sees it.
// Comment to end of line
/* Multi-line comment */
#include <iostream> // Insert library header file
#include "myfile.h" // Insert file in current directory
#define X some text // Replace X with some text
#define F(a,b) a+b // Replace F(1,2) with 1+2
#define X \
some text // Multiline definition, replace X with "\nsome text"
#undef X // Remove definition
#if defined(X) // Conditional compilation (#ifdef X)
#else // Optional (#ifndef X or #if !defined(X))
#endif // reqd to end #if and #ifdefint x; // Define x to be an integer (for initial value see scope)
int x=255; // Define and initialize x to 255
short s; // at least 16 bits, <= int (signedness not specified)
long l; // At least 32 bits, >= int (signedness not specified)
char c='a'; // Usually 8 bit character, a single addressable value
unsigned char u=255;
signed char s=-1; // char might be either
unsigned long x =
0xffffffffL; // short, int, long are signed
float f; // single precision, 32 bits, 8 digits precision, range e+38
double d; // Double precision, 64 bits, 15 digits precision, range e+308
bool b=true; // true or false, may also use int (nonzero is true)
int a, b, c; // Multiple declarations
int a[10]; // Array of 10 ints (a[0] through a[9])
int a[]={0,1,2}; // Initialized array (or a[3]={0,1,2}; )
int a[2][2]={{1,2},{4,5}}; // Array of array of ints
int a[10] = {0,5}; // All unspecified elements are initialized to 0
char s[]="hello"; // Legacy C String (6 elements including '\0')
std::string s = "Hello" // C++ string object with value "Hello"
std::string s = R"(Hello
World)"; // Raw string may contain newline: "Hello\nWorld"
int* p; // p is a pointer to (address of) int
int *p; // same as above, spaces don't matter
int* p = NULL; // ancient C style pointer to nothing
int* p = 0; // old C++ style 0 means null pointer
int* p = nullptr; // modern C++ nullptr
const char* s="hello"; // s points to unnamed array containing "hello"
void* p=nullptr; // Address of untyped memory (nullptr is 0)
int& r=x; // r is a reference to (alias of) int x
enum weekend {SAT,SUN}; // old style enumerated type, SAT=0, SUN=1
weekend w = SAT; // set enumerated variable to value
weekend w = 0; // put in int equivalent to SAT
weekend w = 19; // C++ allows putting in a bad value
enum weekend day; // day is a variable of type weekend
enum weekend{SAT=0,SUN=1}; // Explicit representation as int
enum {SAT,SUN} day; // Anonymous enum
enum class Color {Red,Blue};// Color is a strict type with values Red and Blue
Color x = Color::Red; // Assign Color x to red
typedef String char*; // String s; means char* s;
const int c = 3; // Constants must be initialized, cannot be modified
const int* p=a; // Value pointed to by p cannot be modified
int* const p=a; // the pointer cannot change (but elements can)
const int* const p=a; // Both p and its contents are constant
const int& cr=x; // cr cannot be assigned to change x
int8_t,int16_t,int32_t,
int64_t // signed portable integer types
uint8_t,int16_t,uint32_t,
uint64_t // unsigned portable integer types
auto it = m.begin(); // Declares it to the result of m.begin()
auto const param = config["param"];
// Declares it to the const result
auto& s = singleton::instance();
// Declares it to a reference of the result255, 0377, 0xff // Integers (decimal, octal, hex)
10110011000b // integer (binary)
2147483647L, 0x7fffffffl // Long (>= 32-bit) integers
4200000000U, 0xFFFFFFFFU // unsigned int (32-bit)
123456789012345678ULL // unsigned long long
123.0f, -1.2345678e-38f // single precision floating point literals
123.0, 1.23456789012345e+308// double precision floating point literals
1.5L // long double literal
'a', '\141', '\x61' // Character (literal, octal, hex)
'\n', '\t', '\\', '\'', '\"'// Newline, tab, backslash, single quote, double quote
"string\n" // Array of characters ending with newline and \0
"hello" "world" // Concatenated strings
true, false // bool constants 1 and 0
nullptr // Pointer to nothing with the address of 0int x; // global variable, initialized to 0
int glob = 1921; // initialized global variable
static int y; // global lifetime, scope is this file, default = 0
extern int z; // someone else must have defined this global or linker error
void f() {
int x; // Auto (memory exists only while in scope, not initialized)
int a = 2; // auto, initialized every time function is entered
static int z; // initialized once at start of program to 0
static int w = 13; // initialized once at start of program to 13
}
if local scope
extern int x; // Information only, declared elsewhere; // Empty statement, does nothing
5+6; // Expression, no code generated
x=y; // Assignment
int x; // Declarations are statements
{ // A block is a single statement
int x; // Scope of x is from declaration to end of block
}
if (x) a; // If x is true (not 0), evaluate a
else if (y) b; // If not x and y (optional, may be repeated)
else c; // If not x and not y (optional)
while (x) a; // Repeat 0 or more times while x is true
for (x; y; z) a; // Equivalent to: x; while(y) {a; z;}
for (x : y) a; // Range-based for loop e.g.
// for (auto& x in someList) x.y();
do a; while (x); // Equivalent to: a; while(x) a;
switch (x) { // x must be int
case X1: a; // If x == X1 (must be a const), jump here
case X2: b; // Else if x == X2, jump here
default: c; // Else jump here (optional)
}
break; // Jump out of while, do, or for loop, or switch
continue; // Jump to bottom of while, do, or for loop
return x; // Return x from function to caller
try { a; }
catch (T t) { b; } // If a throws a T, then jump here
catch (...) { c; } // If a throws something else, jump hereint f(int x, int y); // f is a function taking 2 ints and returning int
void f(); // f is a procedure taking no arguments
void f(int a=0); // f() is equivalent to f(0)
f(); // Default return type is int
inline f(); // Optimize for speed
f() { statements; } // Function definition (must be global)
T operator+(T x, T y); // a+b (if type T) calls operator+(a, b)
T operator-(T x); // -a calls function operator-(a)
T operator++(int); // postfix ++ or -- (parameter ignored)
extern "C" {void f();} // f() was compiled in CFunction parameters and return values may be of any type. A function must either be declared or defined before it is used. It may be declared first and defined later. Every program consists of a set of a set of global variable declarations and a set of function definitions (possibly in separate files), one of which must be:
int main() { statements... } // or
int main(int argc, char* argv[]) { statements... }argv is an array of argc strings from the command line.
By convention, main returns status 0 if successful, 1 or higher for errors.
Functions with different parameters may have the same name (overloading). Operators except :: . .* ?: may be overloaded.
Precedence order is not affected. New operators may not be created.
Operators are grouped by precedence, highest first. Unary operators and assignment evaluate right to left. All others are left to right. Precedence does not affect order of evaluation, which is undefined. There are no run time checks for arrays out of bounds, invalid pointers, etc.
T::X // Name X defined in class T
N::X // Name X defined in namespace N
::X // Global name X
t.x // Member x of struct or class t
p-> x // Member x of struct or class pointed to by p
a[i] // i'th element of array a
f(x,y) // Call to function f with arguments x and y
T(x,y) // Object of class T initialized with x and y
x++ // Add 1 to x, evaluates to original x (postfix)
x-- // Subtract 1 from x, evaluates to original x
typeid(x) // Type of x
typeid(T) // Equals typeid(x) if x is a T
dynamic_cast< T>(x) // Converts x to a T, checked at run time.
static_cast< T>(x) // Converts x to a T, not checked
reinterpret_cast< T>(x) // Interpret bits of x as a T
const_cast< T>(x) // Converts x to same type T but not const
sizeof x // Number of bytes used to represent object x
sizeof(T) // Number of bytes to represent type T
++x // Add 1 to x, evaluates to new value (prefix)
--x // Subtract 1 from x, evaluates to new value
~x // Bitwise complement of x
!x // true if x is 0, else false (1 or 0 in C)
-x // Unary minus
+x // Unary plus (default)
&x // Address of x
*p // Contents of address p (*&x equals x)
new T // Address of newly allocated T object
new T(x, y) // Address of a T initialized with x, y
new T[x] // Address of allocated n-element array of T
delete p // Destroy and free object at address p
delete[] p // Destroy and free array of objects at p
(T) x // Convert x to T (obsolete, use .._cast<T>(x))
x * y // Multiply
x / y // Divide (integers round toward 0)
x % y // Modulo (result has sign of x)
x + y // Add, or \&x[y]
x - y // Subtract, or number of elements from *x to *y
x << y // x shifted y bits to left (x * pow(2, y))
x >> y // x shifted y bits to right (x / pow(2, y))
x < y // Less than
x <= y // Less than or equal to
x > y // Greater than
x >= y // Greater than or equal to
x & y // Bitwise and (3 & 6 is 2)
x ^ y // Bitwise exclusive or (3 ^ 6 is 5)
x | y // Bitwise or (3 | 6 is 7)
x && y // x and then y (evaluates y only if x (not 0))
x || y // x or else y (evaluates y only if x is false (0))
x = y // Assign y to x, returns new value of x
x += y // x = x + y, also -= *= /= <<= >>= &= |= ^=
x ? y : z // y if x is true (nonzero), else z
throw x // Throw exception, aborts if not caught
x , y // evaluates x and y, returns y (seldom used)class T { // A new type
private: // Section accessible only to T's member functions
protected: // Also accessible to classes derived from T
public: // Accessible to all
int x; // Member data
void f(); // Member function
void g() {return;} // Inline member function
void h() const; // Does not modify any data members
int operator+(int y); // t+y means t.operator+(y)
int operator-(); // -t means t.operator-()
T(): x(1) {} // Constructor with initialization list
T(const T& t): x(t.x) {}// Copy constructor
T& operator=(const T& t)
{x=t.x; return *this; } // Assignment operator
~T(); // Destructor (automatic cleanup routine)
explicit T(int a); // Allow t=T(3) but not t=3
T(float x): T((int)x) {}// Delegate constructor to T(int)
operator int() const
{return x;} // Allows int(t)
friend void i(); // Global function i() has private access
friend class U; // Members of class U have private access
static int y; // Data shared by all T objects
static void l(); // Shared code. May access y but not x
class Z {}; // Nested class T::Z
typedef int V; // T::V means int
};
void T::f() { // Code for member function f of class T
this->x = x;} // this is address of self (means x=x;)
int T::y = 2; // Initialization of static member (required)
T::l(); // Call to static member
T t; // Create object t implicit call constructor
t.f(); // Call method f on object t
struct T { // Equivalent to: class T { public:
virtual void i(); // May be overridden at run time by derived class
virtual void g()=0; }; // Must be overridden (pure virtual)
class U: public T { // Derived class U inherits all members of base T
public:
void g(int) override; }; // Override method g
class V: private T {}; // Inherited members of T become private
class W: public T, public U {};
// Multiple inheritance
class X: public virtual T {};
// Classes derived from X have base T directlyAll classes have a default copy constructor, assignment operator, and destructor, which perform the corresponding operations on each data member and each base class as shown above. There is also a default no-argument constructor (required to create arrays) if the class has no constructors. Constructors, assignment, and destructors do not inherit.
template <class T> T f(T t);// Overload f for all types
template <class T> class X {// Class with type parameter T
X(T t); }; // A constructor
template <class T> X<T>::X(T t) {}
// Definition of constructor
X<int> x(3); // An object of type "X of int"
template <class T, class U=T, int n=0>
// Template with default parametersnamespace N {class T {};} // Hide name T
N::T t; // Use name T in namespace N
using namespace N; // Make T visible without N::#include <memory> // Include memory (std namespace)
shared_ptr<int> x; // Empty shared_ptr to a integer on heap. Uses reference counting for cleaning up objects.
x = make_shared<int>(12); // Allocate value 12 on heap
shared_ptr<int> y = x; // Copy shared_ptr, implicit changes reference count to 2.
cout << *y; // Dereference y to print '12'
if (y.get() == x.get()) { // Raw pointers (here x == y)
cout << "Same";
}
y.reset(); // Eliminate one owner of object
if (y.get() != x.get()) {
cout << "Different";
}
if (y == nullptr) { // Can compare against nullptr (here returns true)
cout << "Empty";
}
y = make_shared<int>(15); // Assign new value
cout << *y; // Dereference x to print '15'
cout << *x; // Dereference x to print '12'
weak_ptr<int> w; // Create empty weak pointer
w = y; // w has weak reference to y.
if (shared_ptr<int> s = w.lock()) { // Has to be copied into a shared_ptr before usage
cout << *s;
}
unique_ptr<int> z; // Create empty unique pointers
unique_ptr<int> q;
z = make_unique<int>(16); // Allocate int (16) on heap. Only one reference allowed.
q = move(z); // Move reference from z to q.
if (z == nullptr){
cout << "Z null";
}
cout << *q;
shared_ptr<B> r;
r = dynamic_pointer_cast<B>(t); // Converts t to a shared_ptr<B>
#include <cmath> // Include cmath (std namespace)
sin(x); cos(x); tan(x); // Trig functions, x (double) is in radians
asin(x); acos(x); atan(x); // Inverses
atan2(y, x); // atan(y/x)
sinh(x); cosh(x); tanh(x); // Hyperbolic sin, cos, tan functions
exp(x); log(x); log10(x); // e to the x, log base e, log base 10
pow(x, y); sqrt(x); // x to the y, square root
ceil(x); floor(x); // Round up or down (as a double)
fabs(x); fmod(x, y); // Absolute value, x mod y#include <cassert> // Include iostream (std namespace)
assert(e); // If e is false, print message and abort
#define NDEBUG // (before #include <assert.h>), turn off assert#include <iostream> // Include iostream (std namespace)
cin >> x >> y; // Read words x and y (any type) from stdin
cout << "x=" << 3 << endl; // Write line to stdout
cerr << x << y << flush; // Write to stderr and flush
c = cin.get(); // c = getchar();
cin.get(c); // Read char
cin.getline(s, n, '\n'); // Read line into char s[n] to '\n' (default)
if (cin) // Good state (not EOF)?
// To read/write any type T:
istream& operator>>(istream& i, T& x) {i >> ...; x=...; return i;}
ostream& operator<<(ostream& o, const T& x) {return o << ...;}#include <fstream> // Include filestream (std namespace)
ifstream f1("filename"); // Open text file for reading
if (f1) // Test if open and input available
f1 >> x; // Read object from file
f1.get(s); // Read char or line
f1.getline(s, n); // Read line into string s[n]
ofstream f2("filename"); // Open file for writing
if (f2) f2 << x; // Write to file#include <string> // Include string (std namespace)
string s1, s2="hello"; // Create strings
s1.size(), s2.size(); // Number of characters: 0, 5
s1 += s2 + ' ' + "world"; // Concatenation
s1 == "hello world" // Comparison, also <, >, !=, etc.
s1[0]; // 'h'
s1.substr(m, n); // Substring of size n starting at s1[m]
s1.c_str(); // Convert to const char*
s1 = to_string(12.05); // Converts number to string
getline(cin, s); // Read line ending in '\n'#include <vector> // Include vector (std namespace)
vector<int> a(10); // a[0]..a[9] are int (default size is 0)
vector<int> b{1,2,3}; // Create vector with values 1,2,3
a.size(); // Number of elements (10)
a.push_back(3); // Increase size to 11, a[10]=3
a.back()=4; // a[10]=4;
a.pop_back(); // Decrease size by 1
a.front(); // a[0];
a[20]=1; // Crash: not bounds checked
a.at(20)=1; // Like a[20] but throws out_of_range()
for (int& p : a)
p=0; // C++11: Set all elements of a to 0
for (vector<int>::iterator p=a.begin(); p!=a.end(); ++p)
*p=0; // C++03: Set all elements of a to 0
vector<int> b(a.begin(), a.end()); // b is copy of a
vector<T> c(n, x); // c[0]..c[n-1] init to x
T d[10]; vector<T> e(d, d+10); // e is initialized from ddeque<T> is like vector<T>, but also supports:
#include <deque> // Include deque (std namespace)
a.push_front(x); // Puts x at a[0], shifts elements toward back
a.pop_front(); // Removes a[0], shifts toward front#include <utility> // Include utility (std namespace)
pair<string, int> a("hello", 3); // A 2-element struct
a.first; // "hello"
a.second; // 3map (associative array - usually implemented as binary search trees - avg. time complexity: O(log n))
#include <map> // Include map (std namespace)
map<string, int> a; // Map from string to int
a["hello"] = 3; // Add or replace element a["hello"]
for (auto& p:a)
cout << p.first << p.second; // Prints hello, 3
a.size(); // 1#include <unordered_map> // Include map (std namespace)
unordered_map<string, int> a; // Map from string to int
a["hello"] = 3; // Add or replace element a["hello"]
for (auto& p:a)
cout << p.first << p.second; // Prints hello, 3
a.size(); // 1set (store unique elements - usually implemented as binary search trees - avg. time complexity: O(log n))
#include <set> // Include set (std namespace)
set<int> s; // Set of integers
s.insert(123); // Add element to set
if (s.find(123) != s.end()) // Search for an element
s.erase(123);
cout << s.size(); // Number of elements in setunordered_set (store unique elements - usually implemented as a hash set - avg. time complexity: O(1))
#include <unordered_set> // Include set (std namespace)
unordered_set<int> s; // Set of integers
s.insert(123); // Add element to set
if (s.find(123) != s.end()) // Search for an element
s.erase(123);
cout << s.size(); // Number of elements in set#include <algorithm> // Include algorithm (std namespace)
min(x, y); max(x, y); // Smaller/larger of x, y (any type defining <)
swap(x, y); // Exchange values of variables x and y
sort(a, a+n); // Sort array a[0]..a[n-1] by <
sort(a.begin(), a.end()); // Sort vector or deque
reverse(a.begin(), a.end()); // Reverse vector or deque#include <chrono> // Include chrono
using namespace std::chrono; // Use namespace
auto from = // Get current time_point
high_resolution_clock::now();
// ... do some work
auto to = // Get current time_point
high_resolution_clock::now();
using ms = // Define ms as floating point duration
duration<float, milliseconds::period>;
// Compute duration in milliseconds
cout << duration_cast<ms>(to - from)
.count() << "ms";#include <thread> // Include thread
unsigned c =
hardware_concurrency(); // Hardware threads (or 0 for unknown)
auto lambdaFn = [](){ // Lambda function used for thread body
cout << "Hello multithreading";
};
thread t(lambdaFn); // Create and run thread with lambda
t.join(); // Wait for t finishes
// --- shared resource example ---
mutex mut; // Mutex for synchronization
condition_variable cond; // Shared condition variable
const char* sharedMes // Shared resource
= nullptr;
auto pingPongFn = // thread body (lambda). Print someone else's message
[&](const char* mes){
while (true){
unique_lock<mutex> lock(mut);// locks the mutex
do {
cond.wait(lock, [&](){ // wait for condition to be true (unlocks while waiting which allows other threads to modify)
return sharedMes != mes; // statement for when to continue
});
} while (sharedMes == mes); // prevents spurious wakeup
cout << sharedMes << endl;
sharedMes = mes;
lock.unlock(); // no need to have lock on notify
cond.notify_all(); // notify all condition has changed
}
};
sharedMes = "ping";
thread t1(pingPongFn, sharedMes); // start example with 3 concurrent threads
thread t2(pingPongFn, "pong");
thread t3(pingPongFn, "boing");#include <future> // Include future
function<int(int)> fib = // Create lambda function
[&](int i){
if (i <= 1){
return 1;
}
return fib(i-1)
+ fib(i-2);
};
future<int> fut = // result of async function
async(launch::async, fib, 4); // start async function in other thread
// do some other work
cout << fut.get(); // get result of async function. Wait if needed.#include <random>
std::default_random_engine gen; // generates bits
uint32_t x = gen(); // generate 32 bits
std::uniform_int_distribution<int> dist(1,6); // uniform number 1 to 6
int dice_roll = distribution(generator); // get a random number 1 to 6
std::poisson_distribution<int> pdist(5.2);
std::exponential_distribution<double> expo(3.5); // $p(x|\lambda)=\lambda{}e^{-\lambda{}x}$
std::gamma_distribution<double> gdist(2,2);
std::weibull_distribution<double> wdist(2,4);
std::linear_congruential_engine gen2; // different kinds of generators
std::mersenne_twister_engine gen3;
std::subtract_with_carry_engine gen4;
std::normal_distribution<double> N(0,1); // normal with mean=0 and variance=1