[New] Light-weight cross-platform memory-mapped file.

Author: buck-yeh

README.md

@@ -169,6 +169,7 @@
 
 ### System
 
+- [FileAsMem.h](include/bux/FileAsMem.h) - [Memory-mapped file](https://en.wikipedia.org/wiki/Memory-mapped_file)
 - [FsUtil.h](include/bux/FsUtil.h) - Utilities solely related to [\<filesystem\>](https://en.cppreference.com/w/cpp/header/filesystem)
 - [XConsole.h](include/bux/XConsole.h) - Cross-platform console functions.
 - [XPlatform.h](include/bux/XPlatform.h) - Conditionally defined macros, types, functions for as many platforms as possible.

include/bux/FileAsMem.h

@@ -0,0 +1,30 @@
+#pragma once
+#ifdef _WIN32
+#include <windows.h>
+#endif
+#include <filesystem>
+
+namespace bux {
+
+class C_FileAsMemory
+{
+public:
+
+    // Nonvirtuals
+    C_FileAsMemory(const std::filesystem::path& path);
+    ~C_FileAsMemory();
+    const char* data() const { return m_data; }
+
+private:
+
+    // Data
+    char*       m_data{};
+#ifdef _WIN32
+    HANDLE      m_handle{};
+#else
+    size_t      m_bytes{};
+    int         m_fd = -1;
+#endif
+};
+
+} // namespace bux

src/CMakeLists.txt

@@ -8,7 +8,7 @@ message(DEBUG "XCONSOLE_CPP = ${XCONSOLE_CPP}")
 add_library(bux STATIC
         AtomiX.cpp
         EZArgs.cpp EZScape.cpp
-        FA.cpp FileLog.cpp
+        FA.cpp FileAsMem.cpp FileLog.cpp
         LexBase.cpp LogStream.cpp LR1.cpp GLR.cpp ParserBase.cpp Logger.cpp ParaLog.cpp
         ScannerBase.cpp Serialize.cpp StrUtil.cpp SyncLog.cpp
         UnicodeCvt.cpp

src/FileAsMem.cpp

@@ -0,0 +1,54 @@
+#include "FileAsMem.h"
+#ifndef _WIN32
+#include <sys/mman.h>           // mmap(), munmap()
+#include <fcntl.h>              // open()
+#include <unistd.h>             // lseek()
+#endif
+#include <stdexcept>            // std::runtime_error
+
+namespace bux {
+
+C_FileAsMemory::C_FileAsMemory(const std::filesystem::path& path)
+{
+#ifdef _WIN32
+    const auto hFile = CreateFileW(path.c_str(), GENERIC_READ, FILE_SHARE_READ, nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
+    if (hFile == INVALID_HANDLE_VALUE)
+        throw std::runtime_error{"Failed to open \" + path.string() + \" for read-only"};
+
+    m_handle = CreateFileMappingW(hFile, nullptr, PAGE_READONLY, 0, 0, nullptr);
+    CloseHandle(hFile);
+    if (!m_handle)
+        throw std::runtime_error{"Failed to create file mapping"};
+
+    m_data = static_cast<char*>(MapViewOfFile(m_handle, FILE_MAP_READ, 0, 0, 0));
+    if (!m_data)
+        CloseHandle(m_handle);
+#else
+    m_fd = open(path.c_str(), O_RDONLY);
+    if (m_fd == -1)
+        throw std::runtime_error{"Failed to open \"" + path.string() + "\" for read-only"};
+
+    m_bytes = (size_t)lseek(m_fd, 0, SEEK_END);
+    auto data = mmap(nullptr, m_bytes, PROT_READ, MAP_PRIVATE, m_fd, 0);
+    if (data != MAP_FAILED)
+        m_data = static_cast<char*>(data);
+    else
+        close(m_fd);
+#endif
+}
+
+C_FileAsMemory::~C_FileAsMemory()
+{
+    if (m_data)
+    {
+#ifdef _WIN32
+        UnmapViewOfFile(m_data);
+        CloseHandle(m_handle);
+#else
+        munmap(m_data, m_bytes);
+        close(m_fd);
+#endif
+    }
+}
+
+} // namespace bux