rapidio

An easy-to-use C++ 20 Win32 header-only memory-mapping library

Quick Start

Creating a new file

To create a new file, call rapidio::FileView::CreateViewForNewFile(). You can then write to that file view by passing a std::string to view.Write() Note that CreateViewForNewFile() and CreateViewFromExistingFile() return a std::optional, and will return std::nullopt if the construction of the file view fails. Any errors are logged to STDERR.

#include <rapidio.hpp>
#include <string>

int main()
{
  using namespace rapidio;

  // Not necessary, but we can provide an initial size to our FileView making it already create a file of that size
  size_t wantedFileSize = 12; // Hello World!

  FileView fileView = FileView::CreateViewForNewFile("somefile.txt", wantedFileSize).value();
  fileView.Write("Hello World!");

  fileView.Write("We can easily write more data");
  // Done!
}

Accessing an existing file

To access an existing file, call rapidio::FileView::CreateViewFromExistingFile(). You must select either ReadWrite or ReadOnly access.

#include <rapidio.hpp>
#include <string>

int main()
{
  using namespace rapidio;

  FileView fileView = FileView::CreateViewFromExistingFile("somefile.txt", FileAccessMode::ReadOnly, FileOpenMode::OpenExisting).value();
  std::string helloWorld = fileView.Read(12);
  // Filepointer has moved 12 bytes
  std::string nextData = fileView.Read(24);
  // We can go back to the start of the file by calling Seek()
  fileView.Seek(0);
  std::string helloWorldAgain = fileView.Read(12);
  // Done!
}

Performance

You can find the (simple) benchmarks in the repository, run on a desktop with 32GB RAM, and AMD Ryzen 9 5900X 12-Core Processor @ 3.70 GHz

• RapidIO writing 100 MB to a new file (on average over 100 iterations): 60 milliseconds
• STL writing 100 MB to a new file (on average over 100 iterations): 226 milliseconds (~376% slower than RapidIO)
• RapidIO reading 100 MB of an existing file (on average over 100 iterations): 39 milliseconds
• STL reading 100 MB of an existing file (on average over 100 iterations): 833 milliseconds (~2135% slower than RapidIO)

Future Work

• Add Linux support
• Filemappings are currently re-mapped to the entire file when re-allocated, they should grow linearly
• Make this library no longer header-only to avoid including <Windows.h>