Stream Objects
Input Objects
Output Objects
A stream is a sequence of items with no clear boundary
In C++, a stream is a sequence of bytes
Input streams receive bytes from a source and store it in the application memory
Output streams forward bytes from the application memory into a destination
The iostream library defines a number of objects and functions to deal with command line inputs and outputs
The fstream library defines a number of objects and functions to deal with reading/writing from/to files
std::cin is an object of the class istream
std::cout is an object of the class ostream
Both initiated when compiling the iostream library
std::cin is frequently used with the overloaded extraction operator: >> (which can be chained)
std::cin >> var takes a user input and stores in the variable var
The application will try to match the type of the input to the type of var
std::cin uses whitespaces as separators
#include <iostream>
int main()
{
int i;
char c;
double x;
char s[4];
std::cout << "Enter an integer, a character,"
<< " a double and a string : " << std::endl;
//std::cin >> i;
//std::cin >> c;
//std::cin >> x;
//std::cin >> s;
// or, equivalently
std::cin >> i >> c >> x >> s;
std::cout << "Entered " << i << ' ' << c
<< ' ' << x << ' ' << s << std::endl;
return 0;
}
There can be overflown when reading into a char array
Use std::cin.get(c) to capture a single character
Use std::cin.get(s, size + 1) to capture a character array with a specific size
Use std::cin.getline() to capture strings with spaces
Flush the buffer with std::cin.ignore()if not sure!
std::cout is frequently used with the overloaded insertion operator
<< (which can be chained)
std::cout's output can be formatted using flags such as
fixed, setprecision, defaultfloat, etc.
The std::endl manipulator inserts a newline and flushes the buffer
C++ has a library to deal with file input/output (IO) operations:
fstream
It allows developers to open files for reading and writing in several modes:
ios::in open for reading
ios::out open for writing
ios::app open for appending
An ofstream object can be used to write files
It contains methods to open a file for streaming: open(), closing it: close(), as well as for checking if a file is open: is_open()
It overloads the insertion operator: << stream operator to write into a file
#include <iostream>
#include <fstream>
int main()
{
std::ofstream write_file;
write_file.open("test.txt", std::ios::out);
if (write_file.is_open())
{
write_file << "Add a line of text to file"
<< std::endl;
write_file << "Second line of text to file"
<< std::endl;
std::cout << "File written!" << std::endl;
}
else
{
std::cout << "Could not open file"
<< std::endl;
}
write_file.close();
return 0;
}
An ifstream object can be used to read files
It also contains methods to open a file for streaming: open(), closing it: close(), as well as for checking if a file is open: is_open()
It overloads the extraction operator: >>, stream operators to read from a file
Use getline() in case there are spaces in the captured array
#include <iostream>
#include <fstream>
int main()
{
std::ifstream read_file;
read_file.open("test.txt", std::ios::in);
if (read_file.is_open())
{
char aux[128];
// read one word from the file
read_file >> aux;
std::cout << aux << std::endl;
// read whole file word by word
while (read_file >> aux)
{
std::cout << aux << std::endl;
}
}
else
{
std::cout << "Could not open file"
<< std::endl;
}
read_file.close();
return 0;
}