CSE 232: C++ Input/Output Manipulation

Built-In and Simple User Defined Types in C++ • int, long, short, char (signed, integer division)

– unsigned versions toounsigned int, unsigned long, etc.

– C++ guarantees a char is one byte in size– Sizes of other types are platform dependent– Can determine using sizeof() , <climits> INT_MAX

• float, double (floating point division)– More expensive in space and time– Useful when you need to describe continuous quantities

• bool– Logic type, takes on values true, false

• enumerationsenum primary_colors {red, blue, yellow};

• Exercise: enumerate truth, character, string, decimal

CSE 232: C++ Input/Output Manipulation

C-style Strings • Arrays of characters“hello, world!” // 14 positions w/ ‘\0’ char greeting[6] = “hello”; char *audience = “world”;

• Can reference specific positions as characters– Useful for some input checking tasks

isalnum (greeting[i]) // array syntax isdigit (audience + i) // pointer syntax

• Can also reference as an entire string– Using functions found in the <cstring> library

if (strcmp (s, “hello”) == 0){...} if (strlen (s) == 1){...}

• Exercise: check argv[1] for “true” or “false”• Exercise: check argv[1] for single character input

CSE 232: C++ Input/Output Manipulation

Program Argument Checking

• Character based checking– There are also useful functions in the <cctype> library– See page 249 of Prata C++ Primer Plus, 5th Ed.

isdigit() // in ‘0’to ‘9’(decimal digit)isxdigit() // in ‘0’to ‘9’, ‘A’ to ‘F’, // or ‘a’ to ‘f’ (hexadecimal digit)isalpha() // in ‘A’ to ‘Z’ or ‘a’ to ‘z’ (letter)islower() // in ‘a’ to ‘z’ (lowercase letter)isupper() // in ‘A’ to ‘Z’ (uppercase letter)isalnum() // alphanumeric (letter or decimal digit)ispunct() // punctuation characterisblank() // blank (space or horizontal tab)

• Exercise: check whether any of the strings passed by argv represent unsigned decimal integers – we’ll allow leading zeroes but not a + or –– if so, print them on separate lines using cout

CSE 232: C++ Input/Output Manipulation

C++ string Class

#include <iostream>#include <string>using namespace std;int main (int, char*[]) { string s; // empty s = “”; // empty s = “hello”; s += “, ”; s = s + “world!”; cout << s << endl; return 0;}

• <string> header file• Various constructors• Assignment operator• Overloaded operators

+= + < >= == []• The last one is really

useful: indexes stringif (s[0] == ‘h’) …

CSE 232: C++ Input/Output Manipulation

Using C++ vs. C-style Strings

#include <string>#include <cstring> // strcmp ...using namespace std;int main (int, char*[]){ char * w = “world”; string sw = “world”; char * h = “hello, ”; string sh = “hello, ”; cout << h << endl; cout << sh << endl; sh += sw; // cannot say h += w; cout << sh << endl; return 0;}

• C-style strings are contiguous arrays of char– Often accessed through pointers

to char (char *)• C++ string class (template)

provides a rich set of overloaded operators

• Often C++ strings do “what you would expect” as a programmer

• Often C-style strings do “what you would expect” as a machine designer

• In this course we’ll focus on the programmer role

CSE 232: C++ Input/Output Manipulation

C++ Input/Output Stream Classes

#include <iostream>using namespace std;int main (int, char*[]){ int i; // cout == std ostream cout << “how many?” << endl; // cin == std istream cin >> i; cout << “You said ” << i << “.” << endl; return 0;}

• <iostream> header file– Use istream for input– Use ostream for output

• Overloaded operators<< ostream insertion operator>> istream extraction operator

• Other methods– ostream: write, put– istream: get, eof, good, clear

• Stream manipulators– ostream: flush, endl, setwidth,

setprecision, hex, boolalpha

CSE 232: C++ Input/Output Manipulation

C++ File I/O Stream Classes

#include <fstream>using namespace std;int main (){ ifstream ifs; ifs.open (“in.txt”); ofstream ofs (“out.txt”); if (ifs.is_open () && ofs.is_open ()) { int i; ifs >> i; ofs << i; } ifs.close (); ofs.close (); return 0;}

• <fstream> header file– Use ifstream for input– Use ofstream for output

• Other methods– open, is_open, close– getline– seekg, seekp

• File modes– in, out, ate, app, trunc, binary

CSE 232: C++ Input/Output Manipulation

C++ String Stream Classes

#include <iostream>#include <fstream>#include <sstream>using namespace std;int main (){ ifstream ifs (“in.txt”); if (ifs.is_open ()) { string line_1, word_1; getline (ifs, line_1); istringstream iss (line_1); iss >> word_1; cout << word_1 << endl; } return 0;}

• <sstream> header file– Use istringstream for input– Use ostringstream for output

• Useful for scanning input– Get a line from file into string– Wrap string in a stream– Pull words off the stream

• Useful for formatting output– Use string as format buffer– Wrap string in a stream– Push formatted values into

stream– Output formatted string to file

CSE 232: C++ Input/Output Manipulation

Using C++ String Stream Classes#include <string>#include <cstring>#include <sstream>using namespace std;int main (int argc, char *argv[]){ if (argc < 3) return 1; ostringstream argsout; argsout << argv[1] << “ ” << argv[2]; istringstream argsin (argsout.str()); float f,g; argsin >> f; argsin >> g; cout << f << “ / ” << g << “ is ” << f/g << endl; return 0;}

• Program gets arguments as C-style strings

• But let’s say we wanted to input floating point values from the command line

• Formatting is tedious and error-prone in C-style strings (sprintf etc.)

• iostream formatting is friendly• Exercise: check whether any

of the strings passed by argv are unsigned decimal integers (leading zeroes still ok)– print their sum if there are any– otherwise print the value 0