Why is C \'s `cin` Significantly Slower Than Python\'s `input()` for Reading Lines from Standard Input, and How Can Performance Be Improved?

Why is reading lines from stdin much slower in C than Python?

Problem:

When comparing Python and C code for reading lines of string input from stdin, Python code executes significantly faster. Despite ensuring proper C implementation, the Python equivalent outperforms it by an order of magnitude.

Default Settings and System Calls:

In Python, input buffering is enabled by default, leading to efficient large chunk reads and fewer system calls. In contrast, C streams are synchronized with stdio, compelling cin to skip input buffering and read characters individually. This choice, intended to prevent conflicts with stdio functions, inadvertently introduces significant overhead.

Performance Optimization:

To improve C performance, include the statement cin.sync_with_stdio(false) at the beginning of main. This disables stream synchronization and permits independent buffering, substantially enhancing input read speed.

Alternative Options:

Another high-performance alternative to cin is fgets, which employs stdio functions for direct input reading.

Comparison Results:

Implementation	Lines per Second
Python (default)	3,571,428
cin (default/naive)	819,672
cin (no sync)	12,500,000
fgets	14,285,714
wc (not fair comparison)	54,644,808

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