cpp cheatsheet
1.0.0
Basierend auf Phillip M. Duxburys C ++-Cheatsheet und herausgegeben von Morten Nobel-Jørgensen. Der Cheatsheet -Fokus liegt sowohl auf der Sprache als auch auf gemeinsamen Klassen aus der Standardbibliothek. C ++ 11 Ergänzungen sind von isocpp.org C ++ 11 Cheatsheet inspiriert.
Ziel ist es, einen kurzen Überblick über die grundlegende, moderne C ++ (C ++ 14) zu geben.
Das Dokument wird unter https://github.com/mortennobel/cpp-teheetsheet gehostet. Kommentare und Feedback werden geschätzt.
// Comment to end of line
/* Multi-line comment */
# include < stdio.h > // Insert standard 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
# undef X // Remove definition
# if defined(X) // Conditional compilation (#ifdef X)
# else // Optional (#ifndef X or #if !defined(X))
# endif // Required after #if, #ifdef 255 , 0377 , 0xff // Integers (decimal, octal, hex)
2147483647L , 0x7fffffffl // Long (32-bit) integers
123.0 , 1.23e2 // double (real) numbers
' a ' , ' 141 ' , ' x61 ' // Character (literal, octal, hex)
' n ' , ' \ ' , ' ' ' , ' " ' // Newline, backslash, single quote, double quote
" string n " // Array of characters ending with newline and
" hello " " world " // Concatenated strings
true , false // bool constants 1 and 0
nullptr // Pointer type with the address of 0 int x; // Declare x to be an integer (value undefined)
int x= 255 ; // Declare and initialize x to 255
short s; long l; // Usually 16 or 32 bit integer (int may be either)
char c= ' a ' ; // Usually 8 bit character
unsigned char u= 255 ;
signed char s=- 1 ; // char might be either
unsigned long x =
0xffffffffL ; // short, int, long are signed
float f; double d; // Single or double precision real (never unsigned)
bool b= true ; // true or false, may also use int (1 or 0)
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
char s[]= " hello " ; // String (6 elements including ' ')
std::string s = " Hello " // Creates string object with value "Hello"
std::string s = R"( Hello
World )" ; // Creates string object with value "HellonWorld"
int * p; // p is a pointer to (address of) int
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}; // weekend is a type with values SAT and SUN
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 assign to
const int * p=a; // Contents of p (elements of a) are constant
int * const p=a; // p (but not contents) are constant
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 , uint8_t , int16_t ,
uint16_t , int32_t , uint32_t ,
int64_t , uint64_t // Fixed length standard 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 result int x; // Auto (memory exists only while in scope)
static int x; // Global lifetime even if local scope
extern int x; // Information only, declared elsewhere x=y; // Every expression is a statement
int x; // Declarations are statements
; // Empty statement
{ // 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 here int 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 CFunktionsparameter und Rückgabewerte können von jedem Typ sein. Eine Funktion muss entweder deklariert oder definiert werden, bevor sie verwendet wird. Es kann zuerst deklariert und später definiert werden. Jedes Programm besteht aus einer Reihe von globalen Variablenerklärungen und einer Reihe von Funktionsdefinitionen (möglicherweise in separaten Dateien), von denen eine sein muss:
int main () { statements... } // or
int main ( int argc, char * argv[]) { statements... } argv ist eine Reihe von argc -Zeichenfolgen aus der Befehlszeile. main 0 zurücksetzt, falls erfolgreich, 1 oder höher für Fehler.
Funktionen mit unterschiedlichen Parametern können denselben Namen (Überladung) haben. Operatoren außer :: . .* ?: Kann überladen werden. Vorrangreihenfolge ist nicht betroffen. Neue Betreiber dürfen nicht erstellt werden.
Die Betreiber werden durch Vorrang, höchste zuerst, gruppiert. Unary Operatoren und Zuordnung bewerten rechts nach links. Alle anderen sind von links nach rechts. Vorrang hat keinen Einfluss auf die Reihenfolge der Bewertung, die undefiniert ist. Es gibt keine Laufzeitprüfungen für Arrays außerhalb der Grenzen, ungültigen Zeiger usw.
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 directlyAlle Klassen haben einen Standardkopiekonstruktor, Zuweisungsoperator und Destruktor, der die entsprechenden Operationen in jedem Datenelement und jede Basisklasse wie oben gezeigt ausführt. Es gibt auch einen Standard-No-Argument-Konstruktor (zum Erstellen von Arrays erforderlich), wenn die Klasse keine Konstruktoren hat. Konstruktoren, Zuordnung und Zerstörer erben nicht.
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 parameters namespace N { class T {};} // Hide name T
N::T t; // Use name T in namespace N
using namespace N ; // Make T visible without N:: memory (Dynamic Memory Management) # 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>
math.h , cmath (schwimmende Punktmathematik) # 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 assert.h , cassert (Debugging Aid) # 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 iostream.h , iostream (ersetzt stdio.h ) # 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 << ...;}fstream.h , fstream (Datei E/A funktioniert wie cin , cout wie oben) # 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 string (Zeichenarray mit variabler Größe) # 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' vector (Array/Stack mit variabler Größe mit integriertem Speicherzuweisung) # 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 d deque (Array Stack -Warteschlange) deque<T> ist wie vector<T> , unterstützt aber auch:
# 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 utility (Paar) # include < utility > // Include utility (std namespace)
pair<string, int > a ( " hello " , 3 ); // A 2-element struct
a.first; // "hello"
a.second; // 3 map (assoziatives Array - normalerweise als binäre Suchbäume implementiert - avg. Zeitkomplexität: 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 unordered_map (assoziatives Array - normalerweise als Hash -Tabelle implementiert - avg. Zeitkomplexität: o (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(); // 1 set (Einzigartige Elemente speichern - normalerweise als binäre Suchbäume implementiert - avg. Zeitkomplexität: 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 set unordered_set (Einzigartige Elemente speichern - normalerweise als Hash -Set implementiert - avg. Zeitkomplexität: 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 algorithm (eine Sammlung von 60 Algorithmen für Sequenzen mit Iteratoren) # 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 chrono (Zeitbezogene Bibliothek) # 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 " ;thread (Multi-Threading-Bibliothek) # 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 " );future (Thread Support Library) # 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.
