Is C `ifstream` Always Slower Than `fscanf`?

Improving IOStream Performance

Various C users that learned C prefer to continue using the printf / scanf family of functions even while coding in C , due to its accessible interface and localization capabilities. However, performance concerns may arise when comparing it to C 's ifstream. Notably, fscanf is observed to consistently outperform ifstream.

Optimization Techniques for IOStreams

To enhance IOStreams performance, consider the following techniques:

Buffering with pubsetbuf()

Increasing the buffer size reduces HDD hits and system calls, thus improving performance. Set the buffer by accessing the streambuf implementation using pubsetbuf().

char Buffer[N];

std::ifstream file("file.txt");

file.rdbuf()->pubsetbuf(Buffer, N);

Locale Handling

Locale can impact performance due to character conversion and complex system calls. Choose the default C locale, which is optimized for minimal conversion and uniformity across machines, to avoid this overhead.

Synchronization with sync_with_stdio()

This parameter did not exhibit notable performance improvements in our testing.

Benchmarks and Results

Our benchmarks using a simple test program reveal varying results across different platforms and compilers. The outcome suggests that the performance of IOStreams is implementation-dependent.

Here are the findings from various benchmarks:

g 4.7.2-2ubuntu1, -O3, Ubuntu 11.10 x86_64

• C 25% faster

g 4.4.5, -O3, Ubuntu Linux 10.10 x86_64

• C 17% faster

g i686-apple-darwin10-g -4.2.1 (GCC) 4.2.1, mac mini, 4GB ram

• C 111% slower

clang 3.8.0-2ubuntu4, Kubuntu 16.04 Linux 4.8-rc3

• C 66% faster

These results emphasize the significance of implementation quality in IOStreams performance optimization.

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