What happens under the hood of std::cout?

std::cout is an instance of the class std::ostream. When data is output to std::cout (operator<<), a chain of actions is triggered:

1. Data formatting: Data is converted into a sequence of characters depending on the current output format (std::ios_base::fmtflags).
2. Buffering: The converted characters are placed into the stream's internal buffer (std::streambuf). This can be a string buffer (std::stringbuf), a file buffer (std::filebuf), or another specialized buffer.
3. Writing to the target device: When the buffer is full, or explicitly flushed (std::cout << std::endl, std::cout.flush()), or when associated with another stream (e.g., std::cin), data from the buffer is written to the output device (the console's standard output stream - stdout).

The connection to stdout is managed through the std::streambuf object associated with std::cout. This streambuf manages the transfer of data from the buffer to the operating system for printing on the console.

#include <iostream>
#include <streambuf> // For understanding streambuf usage

int main() {
    int value = 42;
    // The operator << triggers formatting and writing to cout's buffer
    std::cout << "The answer is: " << value << std::endl; // std::endl flushes the buffer and adds a newline
    return 0;
}