Implement error handling

include/tmp/directory.hpp

@@ -44,7 +44,7 @@ class directory final : public path {
     /// for temporary files. If a prefix is provided to the constructor, the
     /// directory is created in the path <temp dir>/prefix/. The prefix can be
     /// a path consisting of multiple segments.
-    explicit directory(std::string_view prefix = "") : path(prefix, mkdtemp) {}
+    explicit directory(std::string_view prefix = "") : path(prefix, callback) {}
 
     /// Concatenates this directory path with a given @p source
     std::filesystem::path operator/(std::string_view source) const {
@@ -58,6 +58,14 @@ class directory final : public path {
     directory& operator=(directory&&) noexcept = default;    ///< move-assignable
     directory(const directory&) = delete;                    ///< not copy-constructible
     auto operator=(const directory&) = delete;               ///< not copy-assignable
+
+protected:
+    static void callback(char* path) {
+        if (mkdtemp(path) == nullptr) {
+            auto ec = std::error_code(errno, std::system_category());
+            throw error("Cannot create temporary directory", ec);
+        }
+    }
 };
 
 }    // namespace tmp

include/tmp/file.hpp

@@ -79,14 +79,22 @@ class file final : public path {
     file(const file&) = delete;                    ///< not copy-constructible
     auto operator=(const file&) = delete;          ///< not copy-assignable
 
+protected:
+    static void callback(char* path) {
+        if (mkstemp(path) == -1) {
+            auto ec = std::error_code(errno, std::system_category());
+            throw error("Cannot create temporary file", ec);
+        }
+    }
+
 private:
     bool binary;    ///< This file write mode
 
     /// Creates a unique temporary file using the system's default location
     /// for temporary files. If a prefix is provided to the constructor, the
     /// directory is created in the path <temp dir>/prefix/. The prefix can be
     /// a path consisting of multiple segments.
-    explicit file(std::string_view prefix, bool binary) : path(prefix, mkstemp),
+    explicit file(std::string_view prefix, bool binary) : path(prefix, callback),
                                                           binary(binary) {}
 
     /// Returns a stream for this file

include/tmp/path.hpp

@@ -44,17 +44,18 @@ class path {
     }
 
 protected:
+    /// Exception type that should be used by subclasses to signal errors
+    using error = std::filesystem::filesystem_error;
+
     std::filesystem::path underlying;    ///< This file path
 
     /// Creates a unique temporary path using the given constructor function
-    template<typename C>
-    explicit path(std::string_view prefix, C constructor) {
+    explicit path(std::string_view prefix, void(*callback)(char*)) {
         const auto parent = std::filesystem::temp_directory_path() / prefix;
         std::filesystem::create_directories(parent);
 
         std::string arg = parent / "XXXXXX";
-        constructor(arg.data());
-
+        callback(arg.data());
         this->underlying = std::move(arg);
     }