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C++ Standard Library strings. Libraries File I/O C++ string functions Class vector Algorithms Field Width Format Flags. Libraries. #include < iostream > - defines I/O functions Instance of istream : cin – standard input Instances of ostream : cout – standard output

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c standard library strings
C++ Standard Library strings
  • Libraries
  • File I/O
  • C++ string functions
  • Class vector
  • Algorithms
  • Field Width
  • Format Flags
  • #include <iostream> - defines I/O functions
    • Instance of istream:
      • cin – standard input
    • Instances of ostream:
      • cout – standard output
  • #include <fstream> - for file processing
  • #include <iomanip> - for formatting
  • #include <string.h>
    • for C style string functions
  • #include <string>
    • for C++ style string class and functions
  • #include <vector>
    • for the vector class (a vector is a type of array)
  • #include <algorithm>
    • for the sort() function, and other algorithms
stream input classes objects
Stream Input Classes & Objects
  • The istream class supports stream-input operations
    • The predefined object cin is an instance of the istream class
      • Connected to the standard input device (usually the keyboard)
      • cin >> x; //data “flows” in the directions of the arrows

//to the right

stream output classes objects
Stream Output Classes & Objects
  • The ostream class supports stream-onput operations
    • The predefined object cout is an instance of the ostream class
      • Connected to the standard output device (usually the computer screen)
      • cout << x; //data “flows” in the directions of the arrows

//to the left

file input
File Input
  • Syntax for file input: ifstreamobject(inputfile)
    • makes an ifstream object (variable) for file input


  • If the file cannot be opened, the ifstreamobject is NULL

if(NULL==fileInputStream) {

cout << "Cannot open file " << endl;

//quit program

return 1;


file input1
File Input
  • When reading from a file, use eof() function to check for the end of the file
    • Returns nonzero (true) when reach the end of the file, and zero (false) otherwise
  • Function getline(x, y) reads a line from input stream x into C++ style string y

string line; //C++ style string

while(!fileInputStream.eof()) {

getline(fileInputStream, line);

//output to screen



file output
File Output
  • Syntax for file input: ofstreamobject(outputfile)
    • makes an ofstreamobject (variable) for file output


  • If the file cannot be opened, the ofstreamobject is NULL

if(NULL==fileOutputStream) {

cout << "Cannot open file " << endl;

//quit program

return 1;


file output1
File Output
  • When writing to a file, use the ofstreamobject (variable) in place of cout

string line; //C++ style string

while(!fileInputStream.eof()) {

getline(fileInputStream, line);

//write to output file


//output to screen



  • See example file at: getline.cpp
c strings
C++ Strings
  • C++ strings are an array of characters with many built-in functions
  • String initialization:

string sentence = "This is a string.";

  • Can use the subscript operator [ ] to access each character

cout<<sentence[0]<<endl; //T

function find
Function find()
  • The find(x) function returns the index of the start of the matching string x

string sentence = "This is a string.";

cout<<"sentence.find(\"is\") = "<<sentence.find("is")<<endl; //sentence.find("is") = 2

function length
Function length()
  • Function length()will return the number of characters in the string

string sentence = "This is a string.";

cout<<"sentence.length() = "<<sentence.length()<<endl; //17

function substr
Function substr()
  • The function substr(pos,len)returns a substring, starting at character position pos and spans lencharacters

string sentence = "This is a string.";

intlength = sentence.length(); //17

cout<<sentence.substr(0,length/2)<<endl; //This is cout<<sentence.substr(length/2,length); //a string.

  • Standard Template Library (STL)
    • Also called the C++ Standard Library
    • Has template-based classes
    • Implements many common data structures and algorithms
    • Three components of STL
      • Containers
      • Iterators
      • Algorithms
  • Common data structures written as a template class
    • Three types
      • Sequence containers
      • Associative containers
      • Container adapters
    • First class containers
      • Sequence & associative containers
      • Have certain member functions that container adapters do not have
sequence containers
Sequence Containers
  • Linear data structures
  • vector
    • Rapid insertions & deletions at back
    • Direct access to any element
  • deque
    • Rapid insertions & deletions at front or back
    • Direct access to any element
  • list
    • Doubly-linked list
    • Rapid insertions & deletions anywhere
associative containers
Associative Containers
  • Contain key–value pairs
  • set
    • Rapid lookup, no duplicates allowed
  • multiset
    • Rapid lookup, duplicates allowed
  • map
    • One to one mapping, rapid key-based lookup, no duplicates allowed
  • multimap
    • One to one mapping, rapid key-based lookup, duplicates allowed
container adapters
Container Adapters
  • stack
    • Last-in-first-out
  • queue
    • First-in-first-out
  • priority_queue
    • Highest priority element is always the first element out
member functions
Member Functions
  • Common member functions for all STL containers
    • Default constructor, copy constructor, destructor
      • Each container has several overloaded constructors
    • empty()
      • True if no elements in container; false otherwise
    • size()
      • Number of elements in the container
    • operator=
      • Assigns one container to another
member functions ii
Member Functions II
  • operator<
    • True if 1st container is less than the 2nd container
    • Otherwise returns false
  • operator<=, >, >=, ==, !=
    • True if 1st is <=, >, >=, ==, or != 2nd
    • Otherwise returns false
  • swap
    • Swaps the elements of two containers
header files
Header Files




<queue> (has queue & priority_queue)


<map> (has map & multimap)

<set> (has set & multiset)


  • Iterators similar to pointers
    • Used to point to elements of 1st class containers
  • Operators
    • Dereferencing operator (*)
      • Dereferences an iterator, so you can use the element to which it points
    • Increment operator (++)
      • Moves the iterator to the next element of the container
iterators ii
Iterators II
  • Operators
    • begin()
      • Points to the 1st element of the container
    • end()
      • Points one element past the end of the container
      • Is used only in an equality or inequity comparisons
  • Iterator objects
    • iterator points to an element that can be modified
    • const_iterator points to a constant element
vector sequence container
Vector Sequence Container
  • Class vector is a data structure with continuous memory locations (an array)
    • A vector stores elements on the heap, so the size can grow and shrink as needed
    • Can use the subscript operator [ ], as well as the at( ) member function
    • Use function push_back() to add elements to the end of the vector object
    • function size() returns the number of elements
  • See examplevector.cpp
  • STL provides generic algorithms that can be used in most containers
    • Around 70 standard algorithms
  • To sort a vector, use the sort() function from the algorithm library

#include <algorithm>


sort(v2.begin(), v2.end());

field width
Field Width
  • Number of character positions in input or output
    • cout<<setw(n)
      • N is the field width
      • Otherwise fill characters are inserted as padding
      • If the value has more character than N, the full number or character string will be printed
field width1
Field Width

/*see width.cpp*/

#include <iostream>

#include <iomanip>

using namespace std;

int main(){


cout<<123<<endl; // 123

cout<<setw(5)<<123456<<endl; //123456

return 0;


format flags
Format Flags
  • Various format flags to control formatting
  • Controlled by member functions:
    • cout.setf(ios::??) – set a format
    • cout.unsetf(ios::??) – unset a format
    • cout.flags(ios::??) – set format
  • Or by parameterized stream manipulators:
    • cout<<setiosflags(ios::??) – set a format
    • cout<<resetiosflags(ios::??) – unset a format
format flags1
Format Flags
  • ios::right

– right justification

  • ios::left

– left justification

  • ios::internal
    • Number’s sign is left-justified
    • Number’s magnitude is right-justified
format flags2
Format Flags
  • See example code at: format.cpp
  • ios::scientific

– scientific notation

  • ios::uppercase
    • hex numbers, e in scientific notation become uppercase
  • ios::showpos
    • show “+” for positive numbers
format flags3
Format Flags

float originalFormat = cout.flags();

int d = 12345;


// 12345 12345



//12345 12345



//+ 12345

format flags4
Format Flags


cout<<setw(10)<<d<<endl; //+$$$$12345

cout<<setfill('*')<<setw(10)<<d<<endl; //+****12345


cout<<setfill(' ')<<setw(10)<<d<<endl; // 12345


cout<<hex<<12345<<endl; //0x3039


cout<<123.456<<endl; //1.234560E+002

boolean format
Boolean Format
  • Use stream manipulator "boolalpha" to display "bool" values as strings ("true" or "false")
  • Use "noboolalpha" to display as integers (0 or 1)

/*see bool.cpp*/


using namespace std;

int main(){

bool b = true;

cout<<"b="<<boolalpha<<b<<endl; //b=true

cout<<"b="<<noboolalpha<<b<<endl; //b=1

return 0;