C++ Quick Reference Sheet from Hoomanb.com

C++ Quick Reference Sheet from Hoomanb.com

• 1.
  const int c=3; // Constants must be initialized, cannot assign C++ QUICK REFERENCE to const int* p=a; // Contents of p (elements of a) are constant int* const p=a; // p (but not contents) are constant PREPROCESSOR const int* const p=a; // Both p and its contents are constant const int& cr=x; // cr cannot be assigned to change x // Comment to end of line /* Multi-line comment */ STORAGE CLASSES #include <stdio.h> // Insert standard header file #include "myfile.h" // Insert file in current directory #define X some text // Replace X with some text int x; // Auto (memory exists only while in scope) #define F(a,b) a+b // Replace F(1,2) with 1+2 static int x; // Global lifetime even if local scope #define X extern int x; // Information only, declared elsewhere some text // Line continuation #undef X // Remove definition STATEMENTS #if defined(X) // Condional compilation (#ifdef X) #else // Optional (#ifndef X or #if !defined(X)) #endif // Required after #if, #ifdef x=y; // Every expression is a statement int x; // Declarations are statements ; // Empty statement LITERALS { // A block is a single statement int x; // Scope of x is from declaration to end of 255, 0377, 0xff // Integers (decimal, octal, hex) block 2147483647L, 0x7fffffffl // Long (32-bit) integers a; // In C, declarations must precede statements 123.0, 1.23e2 // double (real) numbers } 'a', '141', 'x61' // Character (literal, octal, hex) if (x) a; // If x is true (not 0), evaluate a 'n', '', ''', '"' // Newline, backslash, single quote, double else if (y) b; // If not x and y (optional, may be repeated) quote else c; // If not x and not y (optional) "stringn" // Array of characters ending with newline and 0 while (x) a; // Repeat 0 or more times while x is true "hello" "world" // Concatenated strings true, false // bool constants 1 and 0 for (x; y; z) a; // Equivalent to: x; while(y) {a; z;} do a; while (x); // Equivalent to: a; while(x) a; DECLARATIONS switch (x) { // x must be int case X1: a; // If x == X1 (must be a const), jump here int x; // Declare x to be an integer (value undefined) case X2: b; // Else if x == X2, jump here int x=255; // Declare and initialize x to 255 default: c; // Else jump here (optional) short s; long l; // Usually 16 or 32 bit integer (int may be } either) break; // Jump out of while, do, or for loop, or switch char c='a'; // Usually 8 bit character continue; // Jump to bottom of while, do, or for loop unsigned char u=255; signed char s=-1; // char might be either return x; // Return x from function to caller unsigned long x=0xffffffffL; // short, int, long are signed try { a; } float f; double d; // Single or double precision real (never catch (T t) { b; } // If a throws a T, then jump here unsigned) catch (...) { c; } // If a throws something else, jump here 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]) FUNCTIONS int a[]={0,1,2}; // Initialized array (or a[3]={0,1,2}; ) int a[2][3]={{1,2,3},{4,5,6}}; // Array of array of ints char s[]="hello"; // String (6 elements including '0') int f(int x, int); // f is a function taking 2 ints and returning int* p; // p is a pointer to (address of) int int char* s="hello"; // s points to unnamed array containing "hello" void f(); // f is a procedure taking no arguments void* p=NULL; // Address of untyped memory (NULL is 0) void f(int a=0); // f() is equivalent to f(0) int& r=x; // r is a reference to (alias of) int x f(); // Default return type is int enum weekend {SAT,SUN}; // weekend is a type with values SAT and SUN inline f(); // Optimize for speed enum weekend day; // day is a variable of type weekend f() { statements; } // Function definition (must be global) enum weekend {SAT=0,SUN=1}; // Explicit representation as int T operator+(T x, T y); // a+b (if type T) calls operator+(a, b) enum {SAT,SUN} day; // Anonymous enum T operator-(T x); // -a calls function operator-(a) typedef String char*; // String s; means char* s; T operator++(int); // postfix ++ or -- (parameter ignored) extern "C" {void f();} // f() was compiled in C
• 2.
  Function parameters andreturn 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 x << y // x shifted y bits to left (x * pow(2, y)) declarations and a set of function definitions (possibly in separate files), one of which must be: x >> y // x shifted y bits to right (x / pow(2, y)) x < y // Less than int main() { statements... } or x <= y // Less than or equal to int main(int argc, char* argv[]) { statements... } x > y // Greater than x >= y // Greater than or equal to argv is an array of argc strings from the command line. By convention, main returns status 0 if successful, 1 or higher for errors. x == y // Equals x != y // Not equals Functions with different parameters may have the same name (overloading). Operators except :: . .* ?: may be x & y // Bitwise and (3 & 6 is 2) overloaded. Precedence order is not affected. New operators may not be created. x ^ y // Bitwise exclusive or (3 ^ 6 is 5) EXPRESSIONS x | y // Bitwise or (3 | 6 is 7) x && y // x and then y (evaluates y only if x (not 0)) 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 x || y // x or else y (evaluates y only if x is false checks for arrays out of bounds, invalid pointers, etc. (0)) T::X // Name X defined in class T N::X // Name X defined in namespace N x = y // Assign y to x, returns new value of x ::X // Global name X x += y // x = x + y, also -= *= /= <<= >>= &= |= ^= t.x // Member x of struct or class t x ? y : z // y if x is true (nonzero), else z p->x // Member x of struct or class pointed to by p a[i] // i'th element of array a throw x // Throw exception, aborts if not caught 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 , y // evaluates x and y, returns y (seldom used) x++ // Add 1 to x, evaluates to original x (postfix) x-- // Subtract 1 from x, evaluates to original x typeid(x) // Type of x CLASSES typeid(T) // Equals typeid(x) if x is a T dynamic_cast<T>(x) // Converts x to a T, checked at run time class T { // A new type static_cast<T>(x) // Converts x to a T, not checked private: // Section accessible only to T's member reinterpret_cast<T>(x) // Interpret bits of x as a T functions const_cast<T>(x) // Converts x to same type T but not const protected: // Also accessable to classes derived from T public: // Accessable to all sizeof x // Number of bytes used to represent object x int x; // Member data sizeof(T) // Number of bytes to represent type T void f(); // Member function ++x // Add 1 to x, evaluates to new value (prefix) void g() {return;} // Inline member function --x // Subtract 1 from x, evaluates to new value void h() const; // Does not modify any data members ~x // Bitwise complement of x int operator+(int y); // t+y means t.operator+(y) !x // true if x is 0, else false (1 or 0 in C) int operator-(); // -t means t.operator-() -x // Unary minus T(): x(1) {} // Constructor with initialization list +x // Unary plus (default) T(const T& t): x(t.x) {} // Copy constructor &x // Address of x T& operator=(const T& t) {x=t.x; return *this; } // Assignment operator *p // Contents of address p (*&x equals x) ~T(); // Destructor (automatic cleanup routine) new T // Address of newly allocated T object explicit T(int a); // Allow t=T(3) but not t=3 new T(x, y) // Address of a T initialized with x, y operator int() const {return x;} // Allows int(t) new T[x] // Address of allocated n-element array of T friend void i(); // Global function i() has private access delete p // Destroy and free object at address p friend class U; // Members of class U have private access delete[] p // Destroy and free array of objects at p static int y; // Data shared by all T objects (T) x // Convert x to T (obsolete, use .._cast<T>(x)) static void l(); // Shared code. May access y but not x class Z {}; // Nested class T::Z x * y // Multiply typedef int V; // T::V means int x / y // Divide (integers round toward 0) }; x % y // Modulo (result has sign of x) void T::f() { // Code for member function f of class T this->x = x;} // this is address of self (means x=x;) x + y // Add, or &x[y] int T::y = 2; // Initialization of static member (required) x - y // Subtract, or number of elements from *x to *y T::l(); // Call to static member
• 3.
  struct T { // Equivalent to: class T { public: putc(c, f) // fprintf(f, "%c", c); virtual void f(); // May be overridden at run time by derived putchar(c); // putc(c, stdout); class fgets(s, n, f); // Read line into char s[n] from f. NULL if EOF virtual void g()=0; }; // Must be overridden (pure virtual) gets(s) // fgets(s, INT_MAX, f); no bounds check class U: public T {}; // Derived class U inherits all members of base fread(s, n, 1, f); // Read n bytes from f to s, return number read T fwrite(s, n, 1, f); // Write n bytes of s to f, return number class V: private T {}; // Inherited members of T become private written class W: public T, public U {}; // Multiple inheritance fflush(f); // Force buffered writes to f class X: public virtual T {}; // Classes derived from X have base T fseek(f, n, SEEK_SET); // Position binary file f at n directly ftell(f); // Position in f, -1L if error rewind(f); // fseek(f, 0L, SEEK_SET); clearerr(f); feof(f); // Is f at end of file? All classes have a default copy constructor, assignment operator, and destructor, which perform the ferror(f); // Error in f? corresponding operations on each data member and each base class as shown above. There is also a default no- perror(s); // Print char* s and error message argument constructor (required to create arrays) if the class has no constructors. Constructors, assignment, and clearerr(f); // Clear error code for f destructors do not inherit. remove("filename"); // Delete file, return 0 if OK rename("old", "new"); // Rename file, return 0 if OK TEMPLATES f = tmpfile(); // Create temporary file in mode "wb+" tmpnam(s); // Put a unique file name in char s[L_tmpnam] template <class T> T f(T t); // Overload f for all types template <class T> class X { // Class with type parameter T STDLIB.H, CSTDLIB (Misc. functions) X(T t); }; // A constructor template <class T> X<T>::X(T t) {} // Definition of constructor atof(s); atol(s); atoi(s);// Convert char* s to float, long, int X<int> x(3); // An object of type "X of int" rand(), srand(seed); // Random int 0 to RAND_MAX, reset rand() template <class T, class U=T, int n=0> // Template with default void* p = malloc(n); // Allocate n bytes. Obsolete: use new parameters free(p); // Free memory. Obsolete: use delete exit(n); // Kill program, return status n NAMESPACES system(s); // Execute OS command s (system dependent) getenv("PATH"); // Environment variable or 0 (system dependent) abs(n); labs(ln); // Absolute value as int, long namespace N {class T {};} // Hide name T N::T t; // Use name T in namespace N STRING.H, CSTRING (Character array handling functions) using namespace N; // Make T visible without N:: Strings are type char[] with a '0' in the last element used. C/C++ STANDARD LIBRARY strcpy(dst, src); // Copy string. Not bounds checked strcat(dst, src); // Concatenate to dst. Not bounds checked strcmp(s1, s2); // Compare, <0 if s1<s2, 0 if s1==s2, >0 if s1>s2 Only the most commonly used functions are listed. Header files without .h are in namespace std. File names are strncpy(dst, src, n); // Copy up to n chars, also strncat(), strncmp() actually lower case. strlen(s); // Length of s not counting 0 strchr(s,c); strrchr(s,c);// Address of first/last char c in s or 0 strstr(s, sub); // Address of first substring in s or 0 STDIO.H, CSTDIO (Input/output) // mem... functions are for any pointer types (void*), length n bytes memmove(dst, src, n); // Copy n bytes from src to dst FILE* f=fopen("filename", "r"); // Open for reading, NULL (0) if error memcmp(s1, s2, n); // Compare n bytes as in strcmp // Mode may also be "w" (write) "a" append, "a+" update, "rb" binary memchr(s, c, n); // Find first byte c in s, return address or 0 fclose(f); // Close file f memset(s, c, n); // Set n bytes of s to c fprintf(f, "x=%d", 3); // Print "x=3" Other conversions: "%5d %u %-8ld" // int width 5, unsigned int, long left just. CTYPE.H, CCTYPE (Character types) "%o %x %X %lx" // octal, hex, HEX, long hex "%f %5.1f" // float or double: 123.000000, 123.0 "%e %g" // 1.23e2, use either f or g isalnum(c); // Is c a letter or digit? "%c %s" // char, char* isalpha(c); isdigit(c); // Is c a letter? Digit? "%%" // % islower(c); isupper(c); // Is c lower case? Upper case? sprintf(s, "x=%d", 3); // Print to array of char s tolower(c); toupper(c); // Convert c to lower/upper case printf("x=%d”, 3); // Print to stdout (screen unless redirected) fprintf(stderr, ... // Print to standard error (not redirected) getc(f); // Read one char (as an int) or EOF from f MATH.H, CMATH (Floating point math) ungetc(c, f); // Put back one c to f getchar(); // getc(stdin); sin(x); cos(x); tan(x); // Trig functions, x (double) is in radians
• 4.
  asin(x); acos(x); atan(x);// Inverses STRING (Variable sized character array) atan2(y, x); // atan(y/x) sinh(x); cosh(x); tanh(x);// Hyperbolic exp(x); log(x); log10(x); // e to the x, log base e, log base 10 string s1, s2="hello"; // Create strings pow(x, y); sqrt(x); // x to the y, square root s1.size(), s2.size(); // Number of characters: 0, 5 ceil(x); floor(x); // Round up or down (as a double) s1 += s2 + ' ' + "world"; // Concatenation fabs(x); fmod(x, y); // Absolute value, x mod y s1 == "hello world" // Comparison, also <, >, !=, etc. s1[0]; // 'h' s1.substr(m, n); // Substring of size n starting at s1[m] TIME.H, CTIME (Clock) s1.c_str(); // Convert to const char* getline(cin, s); // Read line ending in 'n' clock()/CLOCKS_PER_SEC; // Time in seconds since program started time_t t=time(0); // Absolute time in seconds or -1 if unknown VECTOR (Variable sized array/stack with built in memory allocation) tm* p=gmtime(&t); // 0 if UCT unavailable, else p->tm_X where X is: sec, min, hour, mday, mon (0-11), year (-1900), wday, yday, isdst vector<int> a(10); // a[0]..a[9] are int (default size is 0) asctime(p); // "Day Mon dd hh:mm:ss yyyyn" a.size(); // Number of elements (10) asctime(localtime(&t)); // Same format, local time a.push_back(3); // Increase size to 11, a[10]=3 a.back()=4; // a[10]=4; a.pop_back(); // Decrease size by 1 ASSERT.H, CASSERT (Debugging aid) a.front(); // a[0]; a[20]=1; // Crash: not bounds checked a.at(20)=1; // Like a[20] but throws out_of_range() assert(e); // If e is false, print message and abort for (vector<int>::iterator p=a.begin(); p!=a.end(); ++p) #define NDEBUG // (before #include <assert.h>), turn off assert *p=0; // Set all elements of a to 0 vector<int> b(a.begin(), a.end()); // b is copy of a NEW.H, NEW (Out of memory handler) 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 set_new_handler(handler); // Change behavior when out of memory void handler(void) {throw bad_alloc();} // Default DEQUE (array/stack/queue) IOSTREAM.H, IOSTREAM (Replaces stdio.h) deque<T> is like vector<T>, but also supports: a.push_front(x); // Puts x at a[0], shifts elements toward back a.pop_front(); // Removes a[0], shifts toward front 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 UTILITY (Pair) c = cin.get(); // c = getchar(); cin.get(c); // Read char pair<string, int> a("hello", 3); // A 2-element struct cin.getline(s, n, 'n'); // Read line into char s[n] to 'n' (default) a.first; // "hello" if (cin) // Good state (not EOF)? a.second; // 3 // 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 << ...;} MAP (associative array) FSTREAM.H, FSTREAM (File I/O works like cin, cout as above) map<string, int> a; // Map from string to int a["hello"]=3; // Add or replace element a["hello"] for (map<string, int>::iterator p=a.begin(); p!=a.end(); ++p) ifstream f1("filename"); // Open text file for reading cout << (*p).first << (*p).second; // Prints hello, 3 if (f1) // Test if open and input available a.size(); // 1 f1 >> x; // Read object from file f1.get(s); // Read char or line f1.getline(s, n); // Read line into string s[n] ALGORITHM (A collection of 60 algorithms on sequences with iterators) ofstream f2("filename"); // Open file for writing if (f2) f2 << x; // Write to file min(x, y); max(x, y); // Smaller/larger of x, y (any type defining <) swap(x, y); // Exchange values of variables x and y IOMANIP.H, IOMANIP (Output formatting) sort(a, a+n); // Sort array a[0]..a[n-1] by < sort(a.begin(), a.end()); // Sort vector or deque cout << setw(6) << setprecision(2) << setfill('0') << 3.1; // print "003.10"