<iostream> Objects Reference

&lt;iostream> Objects Reference

The `iostream header (short for "standard input/output stream") is where the magic of cout, cin` and friends lives. Every program that talks to the console needs it.

The four standard stream objects

All four live in the std namespace, so you normally write std::cout or add using namespace std;.

Stream objects flush behaviour

• cout - "character out". Buffered: output may sit in a buffer until it's flushed.
• cin - "character in". Blocking; waits for the user to press Enter.
• cerr - "character error". Unbuffered; error output appears immediately.
• clog - "character log." Buffered like cout, meant for log messages.

The insertion operator <<

Sends data into a stream. Works with any type that knows how to print itself:

cout << "Total: " << 42 << endl;

• << as an "insertion" operator writes to the output stream.
• Chains of << print in order, left to right.

The extraction operator >>

Pulls a value out of the INPUT stream:

int age;
cin >> age;

• Waits for the user to type a number and press Enter.
• Skips leading whitespace by default.
• With >>, the reading stops at the first whitespace - so it's not great for whole sentences.

The endl and flush manipulators

Both push buffered output to the screen. endl also starts a new line:

cout << "One" << endl;    // newline + flush
cout << "Two" << flush;   // flush, no newline

• endl = newline + flush.
• flush = flush only.
• Prefer '\n' for everyday line breaks (no flush cost); use endl when timing matters (progress bars, logs).

Reading a whole line with getline

cin >> stops at whitespace. When you want the whitespace included, use getline:

string name;
getline(cin, name);  // reads a whole line, including spaces

• Include <string> for std::string.
• After a cin >> x, an Enter may be left behind. Add cin.ignore(); before getline to swallow it.

Stream state: the lazy fix

• cin.fail() is true after a bad read (e.g. typing a letter where a number goes).
• cin.clear() resets the failed flag so cin works again.
• cin.ignore() discards whatever junk is left in the buffer.

Notes

• cout, while in the iostream` header, needs using namespace std; or a std::` prefix.
• cerr is for really gone wrong errors; clog` is for routine log messages.
• Insertion << and extraction >> aren't built-in magic for every type - if you write your own class, you overload them to make it printable.

TL;DR

• cout prints, cin reads, cerr/clog print errors/logs.
• << sends output; >> reads input.
• endl = newline + flush; flush = flush only.
• Wait for cin >> to skip spaces text, so prefer getline(cin, line).