Standard I/O Streams Library
Four Basic Stream Objects
- extern istream cin: The "standard input stream"
- extern ostream cout: The "standard output stream"
- extern ostream cerr: The "standard error stream"
- extern ostream clog: The "standard log stream"
Format Flags
Format Flags -- ios::adjustfield
- ios::left: Left-justify all output
- ios::right: Right-justify all output
- ios::internal: Left-justify sign or base indicator, and right-justify rest of number
Format Flags -- ios::basefield
- ios::dec: Display integers in base 10 (decimal) format. Is set initially.
- ios::oct: Display integers in base 8 (octal) format
- ios::hex: Display integers in base 16 (hexadecimal) format
Format Flags -- ios::floatfield
- ios::fixed: Use fixed point notation when displaying floating-point numbers (the usual convention)
- ios::scientific: Use exponential (i.e., scientific) notation when displaying floating-point numbers
- Neither is set initially and the behavior is obscure.
Format Flags -- misc
- ios::showbase: Show base indicator when displaying integer output
- ios::showpoint: Show decimal point when displaying floating-point numbers (default is 6 significant digits)
- ios::showpos: Show a leading plus sign (+) when displaying positive numbers
Format Flags -- misc
- ios::uppercase: Use uppercase E when displaying exponential or hexadecimal numbers
- ios::boolalpha: Use textual rather than numerical format to read and write boolean values (true and false, rather than 1 and 0)
- ios::skipws: Skip whitespace on input. Is set initially.
- ios::unitbuf: Flush output buffer after each insertion (which really has nothing to do with formatting)
istream
- What's istream
- The class from which cin is instantiated
ios_base::iostate
- eofbit: End-Of-File reached while performing an extracting operation on an input stream.
- failbit: The last input operation failed because of an error related to the internal logic of the operation itself.
- badbit: Error due to the failure of an input/output operation on the stream buffer.
- goodbit: No error. Represents the absence of all the above (the value zero).
istream::setstate
- iostate rdstate ( ) const;
- void setstate ( iostate state );: The same as clear ( rdstate() | state );
- bool eof ( ) const;
- bool good ( ) const;
- void clear ( iostate state = goodbit );
istream::operator>>
- operator>>(short& val);
- operator>>(unsigned short& val);
- operator>>(int& val);
- operator>>(unsigned int& val);
- operator>>(long& val);
- operator>>(unsigned long& val);
- operator>>(float& val);
- operator>>(double& val);
- operator>>(long double& val);
- operator>>(bool& val);
- operator>>(void*& val);
istream::operator>>
- operator>>(char* val);
- If extracted no characters, calls setstate(failbit).
istream::get
- int get();
- Extracts a character from the stream and returns its value (casted to an integer).
- istream& get ( char& c );
- Extracts a character from the stream and stores it in c.
- calls setstate(failbit) if stores no characters
istream::get
- istream& get (char* s, streamsize n, char delim );
- Extracts characters and stores in s until any of the following occurs:
- n-1 characters are stored
- encounters eof
- the next available character is delim (in this case delim is not extracted)
- calls setstate(failbit) if stores no characters
istream::get
- istream& get ( char* s, streamsize n );
- Same as above, except that delim is '\n'
Example
#include <iostream>
#include <fstream>
using namespace std;
int main () {
char c, str[256];
ifstream is;
cout << "Enter the name of an existing text file: ";
cin.get (str,256);
is.open (str); // open file
while (is.good()) // loop while extraction from file is possible
{
c = is.get(); // get character from file
if (is.good())
cout << c;
}
is.close(); // close file
return 0;
}
istream::getline
- istream& getline (char* s, streamsize n, char delim );
- Extracts characters and stores in s until any of the following occurs:
- n-1 characters are stored
- encounters end-of-file
- the next available character is delim (in this case delim is extracted)
- calls setstate(failbit) if stores no characters
Example
#include <iostream>
int main()
{
using namespace std;
const int line_buffer_size = 100;
char buffer[line_buffer_size];
int line_number = 0;
while (cin.getline(buffer, line_buffer_size, ’n’) || cin.gcount()) {
int count = cin.gcount();
if (cin.eof())
cout << "Partial final line";
// cin.fail() is false
else if (cin.fail()) {
cout << "Partial long line";
cin.clear(cin.rdstate() & ̃ios::failbit);
} else {
count--;
// Don’t include newline in count
cout << "Line " << ++line_number;
}
cout << " (" << count << " chars): " << buffer << endl;
}
}
istream::ignore
- istream& ignore ( streamsize n = 1, int delim = EOF );
- Extracts and discards characters until any of the following occurs:
- end-of-file occurs on the input sequence
- c == delim for the next available input character c (in which case c is extracted)
- n characters are extracted
istream::peek
- int peek();
- Returns traits::eof() if good() is false. Otherwise, returns rdbuf()->sgetc().
Example
#include <iostream>
using namespace std;
int main () {
char c;
int n;
char str[256];
cout << "Enter a number or a word: ";
c=cin.peek();
if ( (c >= '0') && (c <= '9') )
{
cin >> n;
cout << "You have entered number " << n << endl;
}
else
{
cin >> str;
cout << " You have entered word " << str << endl;
}
return 0;
}
ios_base::width, ios::fill
- streamsize width ( streamsize wide );
- char fill ( char fillch );
Example
#include <iostream>
using namespace std;
int main ()
{
cout << 100 << endl;
cout.width(10);
cout << 100 << endl;
cout.fill('x');
cout.width(15);
cout << left << 100 << endl;
return 0;
}
- smanip setw ( int n );
Example
#include <iostream>
using namespace std;
int main ()
{
cout << setw(7) << 269 << endl;
cout << 269 << endl;
return 0;
}
ios_base::precision
- streamsize precision ( streamsize prec );
Example
#include <iostream>
using namespace std;
int main () {
double f = 3.14159;
cout.unsetf(ios::floatfield); // floatfield not set
cout.precision(5);
cout << f << endl;
cout.precision(10);
cout << f << endl;
cout.setf(ios::fixed,ios::floatfield); // floatfield set to fixed
cout << f << endl;
return 0;
}