fix: #226 use strerror_s/strerror_r if possible

toml/exception.hpp

@@ -2,8 +2,11 @@
 // Distributed under the MIT License.
 #ifndef TOML11_EXCEPTION_HPP
 #define TOML11_EXCEPTION_HPP
-#include <stdexcept>
+
+#include <array>
 #include <string>
+#include <stdexcept>
+
 #include <cstring>
 
 #include "source_location.hpp"
@@ -11,11 +14,60 @@
 namespace toml
 {
 
+namespace detail
+{
+
+inline std::string str_error(int errnum)
+{
+    // C++ standard strerror is not thread-safe.
+    // C11 provides thread-safe version of this function, `strerror_s`, but it
+    // is not available in C++.
+    // To avoid using std::strerror, we need to use platform-specific functions.
+    // If none of the conditions are met, it calls std::strerror as a fallback.
+#ifdef _MSC_VER // MSVC
+    constexpr std::size_t bufsize = 256;
+    std::array<char, bufsize> buf;
+    buf.fill('\0');
+    const auto result = strerror_s(buf.data(), bufsize, errnum);
+    if(result != 0)
+    {
+        return std::string("strerror_s failed");
+    }
+    else
+    {
+        return std::string(buf.data());
+    }
+#elif defined(_GNU_SOURCE)
+    constexpr std::size_t bufsize = 256;
+    std::array<char, bufsize> buf;
+    buf.fill('\0');
+    const char* result = strerror_r(errnum, buf.data(), bufsize);
+    return std::string(result);
+#elif (defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE >= 200112L) || (defined(_XOPEN_SOURCE) && _XOPEN_SOURCE >= 600)
+    constexpr std::size_t bufsize = 256;
+    std::array<char, bufsize> buf;
+    buf.fill('\0');
+    const int result = strerror_r(errnum, buf.data(), bufsize);
+    if (result != 0)
+    {
+        return std::string("strerror_r failed");
+    }
+    else
+    {
+        return std::string(buf.data());
+    }
+#else // fallback
+    return std::strerror(errnum);
+#endif
+}
+
+} // detail
+
 struct file_io_error : public std::runtime_error
 {
   public:
     file_io_error(int errnum, const std::string& msg, const std::string& fname)
-        : std::runtime_error(msg + " \"" + fname + "\": " + std::strerror(errnum)),
+        : std::runtime_error(msg + " \"" + fname + "\": " + detail::str_error(errnum)),
           errno_(errnum)
     {}
     int get_errno() const noexcept {return errno_;}