Is `scanf()` Really Faster Than `cin` in C : Fact or Fiction?

Is Using scanf() Faster than cin in C Programs?

A common belief among programmers is that using the stdio functions scanf() and printf() is faster than their C counterparts, cin and cout. This question explores this claim and provides empirical evidence.

True or False: scanf() is Faster than cin

As the provided answer demonstrates, scanf() can indeed be significantly faster than cin in C . In the given benchmark, scanf() outperformed cin by a factor of four when processing a large text file containing millions of numbers.

Why the Speed Difference?

The speed difference stems from the underlying implementation of the respective functions. scanf() is implemented in C's standard I/O library, which focuses on efficiency and speed. Cin, on the other hand, is implemented in C 's iostream library, which prioritizes type safety and support for a wide range of data types.

Best Practice: Use scanf() Over cin

Based on the performance results, it may be tempting to always opt for scanf() over cin. However, this practice is not recommended for several reasons:

• Reduced Portability: scanf() is a C-specific function that may not be available in all C implementations.
• Reduced Type Safety: scanf() does not provide type safety checks, which can lead to errors when encountering unexpected data types.
• Deprecated Syntax: scanf() uses a non-standard style of format specifiers, making code more difficult to read and maintain.

An Alternative: std::ios::sync_with_stdio(false)

If performance is a critical consideration, a compromise solution is to call std::ios::sync_with_stdio(false). This disables the synchronization between stdio and iostream, reducing overheads and improving the performance of iostream operations.

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