C++ Standard Libraries

using std namespace; is assumed for these libraries.

iostream
String Stream
cmath
ctime
cstdlib
iomanip
typeinfo
fstream
optional
cctype
pair
tuple
algorithm

iostream

Used for reading user input data from the terminal and outputting to the terminal.

#include <iostream>

Functions	Description
`istream& cin`	Input stream
`ostream& cout`	Output stream. Buffered by default.
`ostream& cerr`	Unbuffered(write to console immediately) error stream
`ostream& clog`	Buffered error stream
`ostream& operator<<(ostream&, constT&)`	Outputs value to stream.
`istream& operator>>(istream&, T&)`	Inputs value split by whitespace, returns false if invalid, newline stays in buffer
`endl`	`\n` and flushes the stream
`int istream.get()`	Gets the next char from the buffer or -1 for EOF
`ostream& ostream.put(char)`	Writes one character
`istream& istream.ignore()`	Ignores the next character
`int istream.peek()`	Returns the next character without indexing.
`bool eof()`	Checks end of file
`bool fail()`	Stream operation fail not from EOF like imputing the wrong type of character
`void istream.clear()`	Clears flags including EOF flag
`ostream& ostream.flush()`	Forces any buffered output to be writhen to the console.
`istream& istream.seekg(offset, pos)`	Moves input pointer to new pos. `ios::beg, cur, end` are common pos

Floats output 99 not 99.0
Can do multiple in one line: cin >> var1 >> var2
Discards white spaces: cin >> ws

String Stream

Used to treat a string as a stream.

#include <sstream>

Functions	Description
`ostringstream`	Output string stream. Used for `<<`s
`istringstream`	Input string stream. Used for `>>`s.
`stringstream`	Input and Output string stream
`stringstream ss(string)`	Creates a string stream
`ss << "string";`	Concatenates to the string stream, but not the constructor string.
`ss >> str;`	Puts the next word into str. Words are separated by spaces.

cmath

Floating point math operations.

#include <cmath>

Functions	Description
`pow(base, exponent)`
`sqrt(x)`
`fabs(x)`	absolute value
`ceil(x)`	Round up
`floor(x)`	Round down
`sin(x)`, `cos(x)`, `tan(x)`
`asin(x)`, `acos(x)`, `atan(x)`	Inverse trig function.
`log(x)`, `log10(x)`	Natural and base 10 log
`exp(x)`	e to the power of x
`fmod(x, y)`	x % y with the same sign as x
`hypot(x, y)`	$\sqrt(x^2 + y^2)$

Trig functions use radians

const double PI = 3.141592653589793;
double _toRadians(double degrees) { return degrees * (PI / 180.0); }
double _toDegrees(double radians) { return radians * (180.0 / PI); }

ctime

Time function.

#include <ctime>

Function	Description
`time_t time(t)`	Current time in seconds since epoch
`double difftime(t1, t2)`	Difference in seconds
`char* ctime(&t)`	Converts time_t to readable string
`tm* localtime(&t)`	Converts time_t to local time struct
`tm* gmtime(&t)`	Converts time_t to UTC time struct
`time_t mktime(&tm)`	Converts tm struct to time_t

cstdlib

Integer math operations.

#include <cstdlib>

Functions	Description
`int abs(x)`
`void srand(seed)`	Seeds random number generator
`int rand()`	Random int from `0` to `RAND_MAX`
`void exit(status)`	Terminates the program with status code. 1 - error

iomanip

Stream input and output formatting.

#include <iomanip>

Function	Description
`setw(n)`	Sets width of next input/output. ANy values larger are ignored.
`setprecision(n)`	Number of digits for floats.
`fixed`	`setprecision` counts after decimal point
`setfill(char)`	Sets extra characters for overflow with `setw(n)`
`right`	Justify right
`left`	Justify left

Examples:
- cout << setprecision(2) << 9.99999; Outputs: 10
- cout << fixed << setprecision(2) << 9.99999; Outputs: 10.00
- cout << setprecision(2) << 146.789; Outputs: 1.5e+02

typeinfo

Gets type of variable.

#include <typeinfo>
typeid(var).name() gives a string of the type of variable.

Returned	Type
`d`	double
`c`	char
`i`	integer
`P`	pointer
`K`	constant

fstream

Reading and writing to files.

#include <fstream>

Function	Description
`ifstream`	Reading from a file
`ofstream`	Writing to a file. Opens a new one if not found.
`fstream`	Reading and writing.
`fstream file("name.txt");`	Opens file
`file.open("name.txt");`	Also opens the file
`file.close();`	Closes a file
`file.is_open()`	Checks if it opened

A file acts like a regular buffer
- file << "concatenate";
- file >> input;
- getline(file, line);

optional

Value that may or may not be present. Helps avoid using null pointers or sentinel values(Ex: End of file).

#include <optional>

Function	Description
`bool has_value()`	Checks if value exists.
`const T& value()`	Gets value. Throws if empty.
`T value_or(default)`	Returns the value or a default if empty
`void reset()`	Makes value empty
`std::nullopt`	Empty value
`optional<int> x = 10;`	Assigns value
`T& emplace(ConstructorArgs...)`	Constructs a new value in place.

cctype

Character functions.

#include <cctype>

Function	Description
`char toupper(char)`	Upper case
`char tolower(char)`	Lower case
`bool isxdigit(char)`	Is hexadecimal numeric character
`bool isupper(char)`	Is upper case character
`bool isspace(char)`	Is a whitespace character. Spaces, tabs, and new lines
`bool ispunct(char)`	Is a punctuation/special character
`bool islower(char)`	Is lower case character
`bool isdigit(char)`	Is a digit
`bool isblank(char)`	Is a space or tab
`bool isalpha(char)`	Is lower or upper case letter
`bool isalnum(char)`	Is lower, upper, or number

pair

Key value pair.

#include <utility>

Function	Description
`.first`	Get or update first value
`.second`	Get or update second value
`pair<T1, T2> make_pair(T1, T2)`	Creates a pair by inferring the type.

tuple

Fixed size collection of values. Useful for returning multiple values from a function instead of using a struct.

#include <tuple>

Function	Description
`size_t tuple_size<decltype(tuple)>::value`	Number of elements in a tuple
`tuple<...> tuple_cat(t1, t2, ...)`	Concatenates tuple2 onto tuple
`T& get<I>(tuple)`	Get and set element at index `I`
`std::tie(v1, v2, ...) = tuple;`	Creates references of each tuple value.
`tuple<...> make_tuple(T1, T2, ...)`	Creates a tuple by inferring the types.

algorithm

Algorithms that use iterators.

#include <algorithm>

Function	Description
`void fill(iterator first, iterator last, value)`	Fills range with values.
`void sort(iterator first, iterator last)`	Sorts range in ascending order.
`OutputIt copy(InputIt first, InputIt last, OutputIt outFirst)`	Copies range to another. Returns outLast.
`iterator find(iterator first, iterator last, value)`	Finds the first occurrence of value.
`size_t count(iterator first, iterator last, value)`	Counts occurrences of value.
`void reverse(iterator first, iterator last)`	Reverses elements in range.