minor improvements

libscio.hpp

@@ -282,21 +282,26 @@ namespace sc {
                 byte_order _saved_byte_order {byte_order::undefined};
         };
 
-		class mapped_file : std::istream {
+        class mapped_file : public std::istream {
             public:
-				mapped_file() = default;
+                mapped_file();
                 mapped_file(const std::string& path);
 
+                // no copying
                 mapped_file(const mapped_file&) = delete;
                 mapped_file& operator=(const mapped_file&) = delete;
 
+                // moving allowed
                 mapped_file(mapped_file&& other);
                 mapped_file& operator=(mapped_file&& other);
 
                 ~mapped_file();
 
+                // it's an error to open an already opened mapped_file
                 void open(const std::string& path);
 
+                // direct (read-only) access to mapped memory
+                const char* mapping() const { return _mapping; }
                 size_t size() const { return _length; }
 
             private:

mapped_file.cpp

@@ -18,6 +18,8 @@
 
 using namespace sc::io;
 
+mapped_file::mapped_file() : std::istream {&_membuf} {}
+
 mapped_file::mapped_file(const std::string& path) : std::istream {&_membuf} {
     open(path);
 }
@@ -47,12 +49,15 @@ mapped_file::mapped_file(mapped_file&& other) {
 }
 
 mapped_file& mapped_file::operator=(mapped_file &&other) {
+    if (&other != this) {
         mapped_file mf {std::move(other)};
         std::swap(mf, *this);
+    }
     return *this;
 }
 
 void mapped_file::open(const std::string& path) {
+    if (_fd != -1) throw std::runtime_error("already open");
     _fd = ::open(path.c_str(), O_RDONLY);
     throw_if_min1_msg(_fd, "could not open file");
     struct stat st;