Mex example: need to map into stdlib.is_char_device

Author: scivision

.gitignore

@@ -1,5 +1,7 @@
 Filesystem.class
 code-coverage/
 test-results/
+.buildtool/
 *.asv
 docs/
+*.mex*

buildfile.m

@@ -1,16 +1,40 @@
 function plan = buildfile
 plan = buildplan(localfunctions);
+
 plan.DefaultTasks = "test";
+
+if ~isMATLABReleaseOlderThan("R2024a")
+  root = plan.RootFolder;
+  bin = fullfile(root, "bin");
+  if ~isfolder(bin), mkdir(bin), end
+  addpath(bin)
+
+  plan("clean") = matlab.buildtool.tasks.CleanTask;
+
+  if ispc
+    compiler_opt = "COMPFLAGS=/EHsc /std:c++17";
+  else
+    compiler_opt = "CXXFLAGS=-std=c++17";
+  end
+
+  plan("mex:is_char_device") = matlab.buildtool.tasks.MexTask("is_char_device.cpp", bin, ...
+    Options=compiler_opt);
+
+  plan("test").Dependencies = "mex";
+end
+
 end
 
+
 function checkTask(~)
 % Identify code issues (recursively all Matlab .m files)
 issues = codeIssues;
 assert(isempty(issues.Issues), formattedDisplayText(issues.Issues))
 end
 
 function testTask(~)
-  addpath(fileparts(mfilename("fullpath")))
+  t = fileparts(mfilename("fullpath"));
+  addpath(t)
 
   r = runtests(IncludeSubfolders=true, strict=true, UseParallel=true, OutputDetail="Concise");
 

is_char_device.cpp

@@ -0,0 +1,94 @@
+// C++ Matlab MEX function using C++17 <filesystem>
+// build examples:
+// * MSVC: mex COMPFLAGS="/EHsc /std:c++17" is_char_device.cpp
+// * GCC: mex CXXFLAGS="-std=c++17" is_char_device.cpp
+
+// https://www.mathworks.com/help/matlab/matlab_external/data-types-for-passing-mex-function-data-1.html
+
+#include "mex.hpp"
+#include "mexAdapter.hpp"
+
+#include <string>
+// note: <string_view> causes compile failures with MSVC at least
+
+#include <vector>
+#include <memory>
+
+#if defined(_MSC_VER)
+# define WIN32_LEAN_AND_MEAN
+# include <windows.h>
+#elif __has_include(<filesystem>)
+# include <filesystem>
+# include <system_error>
+#endif
+
+#include <sys/types.h>
+#include <sys/stat.h>
+
+static int fs_st_mode(std::string path)
+{
+// https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/stat-functions
+  struct stat s;
+
+  return stat(path.data(), &s) == 0 ? s.st_mode : 0;
+}
+
+
+static bool fs_is_char_device(std::string path)
+{
+// character device like /dev/null or CONIN$
+#if defined(_MSC_VER)
+  // currently broken in MSVC STL for <filesystem>
+  HANDLE h =
+    CreateFileA(path.data(), GENERIC_READ, FILE_SHARE_READ,
+                nullptr, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, nullptr);
+  if (h == INVALID_HANDLE_VALUE)
+    return false;
+
+  const DWORD type = GetFileType(h);
+  CloseHandle(h);
+  return type == FILE_TYPE_CHAR;
+#elif defined(__cpp_lib_filesystem)
+  std::error_code ec;
+  return std::filesystem::is_character_file(path, ec) && !ec;
+#else
+  // Windows: https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/fstat-fstat32-fstat64-fstati64-fstat32i64-fstat64i32
+  return S_ISCHR(fs_st_mode(path));
+#endif
+}
+
+
+class MexFunction : public matlab::mex::Function {
+public:
+  void operator()(matlab::mex::ArgumentList outputs, matlab::mex::ArgumentList inputs) {
+// boilerplate engine & ArrayFactory setup
+    std::shared_ptr<matlab::engine::MATLABEngine> matlabPtr = getEngine();
+
+    matlab::data::ArrayFactory factory;
+// boilerplate input checks
+    if (inputs.size() != 1) {
+      matlabPtr->feval(u"error", 0,
+        std::vector<matlab::data::Array>({ factory.createScalar("One input required") }));
+    }
+    if (inputs[0].getType() != matlab::data::ArrayType::MATLAB_STRING) {
+      matlabPtr->feval(u"error", 0,
+        std::vector<matlab::data::Array>({ factory.createScalar("Input must be a string") }));
+    }
+    if (inputs[0].getNumberOfElements() != 1) {
+      matlabPtr->feval(u"error", 0,
+        std::vector<matlab::data::Array>({ factory.createScalar("Input must be a scalar string") }));
+    }
+
+// Matlab strings are an array, so we use [0][0] to get the first element
+    std::string inputStr = inputs[0][0];
+
+// actual function algorithm / computation
+    bool y = fs_is_char_device(inputStr);
+
+// convert to Matlab output -- even scalars are arrays in Matlab
+// https://www.mathworks.com/help/matlab/matlab_external/create-matlab-array-with-matlab-data-cpp-api.html
+// https://www.mathworks.com/help/matlab/apiref/matlab.data.arrayfactory.html
+
+    outputs[0] =  factory.createArray<bool>({1,1}, {y});
+  }
+};

test/TestMex.m

@@ -0,0 +1,22 @@
+classdef TestMex < matlab.unittest.TestCase
+
+methods (Test)
+
+function test_is_char_device(tc)
+tc.assumeFalse(isMATLABReleaseOlderThan("R2024a"), "mex:is_char_device requires Matlab >= R2024a")
+
+% /dev/stdin may not be available on CI systems
+
+if ispc
+  b = is_char_device("NUL");
+else
+  b = is_char_device("/dev/null");
+end
+
+tc.verifyTrue(b)
+
+end
+
+end
+
+end