The cout object is an instance of the ostream class in C++ programming language. This class is defined within the < iostream > header file, where all identifiers are encapsulated within the std namespace. Therefore, the complete reference to cout is std::cout.

Basic Data Type Support

The cout stream supports multiple data types including integers, floating-point numbers, characters, and strings. These data types are automatically converted to string format during output operations.

#include <iostream>
using namespace std;

int main() {
    int number = 1;
    bool flag = true;
    double value = 1.2;
    char symbol = 'c';
    
    cout << "number = " << number << endl
         << "flag = " << flag << endl
         << "symbol = " << symbol << endl
         << "value = " << value << endl;
    
    return 0;
}

File Stream Integration

Output operations can be redirected to file stream objects, enabling content to be written directly to files. The statement std::cout << std::endl; flushes the output buffer, ensuring immediate display of output content.

Character Encoding Considerations

To prevent character encoding issues when displaying Chinese text, use std::wcout for wide character string output. Additionally, include the compilation flag -finput-charset=UTF-8 to specify the input file encoding format.

Numeric Base Conversion

By default, cout displays numbers in decimal format. Alternative numeric bases can be specified using various manipulators:

#include <iostream>
#include <iomanip>
using namespace std;

int main() {
    int num = 90;
    
    cout << num << endl;                           // Default decimal
    cout << dec << num << endl;                 // Decimal format (same as default)
    cout << oct << num << endl;                 // Octal representation
    cout << hex << num << endl;                 // Hexadecimal with lowercase letters
    
    cout << setiosflags(ios::uppercase);          // Enable uppercase letters
    cout << hex << num << endl;                 // Hexadecimal with uppercase letters
    
    cout << setbase(8) << num << endl;          // Set base to 8 (octal)
    
    return 0;
}

Precision Control

To control decimal precision, include the #include <iomanip> header. The expression cout << fixed << setprecision(2) << 1.23456 << endl; formats floating-point numbers to two decimal places.

#include <iostream>
#include <iomanip>
using namespace std;

int main() {
    cout << fixed << setprecision(2) << 1.23456 << endl;
    cout << setprecision(2) << fixed << 1.23456 << endl;
    
    return 0;
}

The order of fixed and setprecision() does not affect the output result. C++ defaults to six significant digits for floating-point output. When integer digits exceed six, scientific notation is used. Precision can be modified through several methods:

• Using setprecision(n) sets the total significant digits for floating-point output
• Using setiosflags(ios::fixed) or fixed controls precision after the decimal point

#include <iostream>
#include <iomanip>
using namespace std;

int main() {
    double sample = 123.456789;
    
    cout << sample << endl;
    cout << setprecision(3) << sample << endl;
    cout << setprecision(9) << sample << endl;
    cout << setiosflags(ios::fixed);
    cout << sample << endl;
    cout << fixed << setprecision(3) << sample << endl;
    cout << setprecision(9) << fixed << sample << endl;
    
    return 0;
}

Sign and Decimal Point Display

Use showpoint and showpos manipulators to control sign and decimal point visibility:

#include <iostream>
#include <iomanip>
using namespace std;

int main() {
    double positive = 5, negative = -1.2;
    
    cout << positive << "\t\t" << negative << endl;
    cout << showpoint << positive << "\t\t" << negative << endl;
    cout << showpos << positive << "\t" << negative << endl;
    
    return 0;
}

Field Width and Alignment

By default, output is right-aligned. Use setw() along with left or right manipulators:

#include <iostream>
#include <iomanip>
using namespace std;

int main() {
    int value = 10;
    
    cout << setw(3) << value << endl;              // Default right alignment
    cout << setw(3) << left << value << endl;      // Left alignment
    cout << setw(3) << right << value << endl;     // Right alignment
    
    return 0;
}

Fill Character Specification

Use setfill() to specify fill characters for padding:

#include <iostream>
#include <iomanip>
using namespace std;

int main() {
    int hours = 14, minutes = 18, seconds = 10;
    
    cout << setw(2) << setfill('0') << hours 
         << ":" << minutes << ":" << seconds;
    
    return 0;
}