2 IO Stream | KaiGuoV5

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c++	function	action
`std::cin`	characters from stdin	reads from buffer
`std::cout`	characters to stdout	writes to buffer first, output to console when buffer full
`std::clog`	characters to stderr	writes to buffer first, output to console when buffer full
`std::cerr`	characters to stderr	immediatly writes to console

Stream Operators

Operator	Meaning	Example
`>>`	"get from"	source `>>` target
`<<`	"put to"	target `<<` source

work for fundamental types and strings (support for other types can be added)

>> reads until next whitespace character (space, tab, newline, …)

can be chained:

🚫

Avoid std::endl!

One often sees something like this in C++ code examples / tutorials:

Each call to std::endl flushes the output buffer and writes the output immediately.

This can lead to serious performance degradation, if done frequently.

C++'s I/O streams use buffers to mitigate the performance impact of (potentially expensive) system input or output operations. Output is collected until a minimum number of characters can be written. Overusing std::endl interferes with this mechanism.

✅

Do This Instead:

\n writes a line break

no premature flush of output buffer

only one call to operator << (each additional call can create a small overhead)

Only use std::endl if you absolutely need to make sure that some output needs to materialize immediately.