Spectre/System/File: add getErrorMessage()

include/Spectre/System/File.h

@@ -4,6 +4,7 @@
 
 #include <stdio.h>
 #include <string>
+#include <system_error>
 
 namespace sp {
 
@@ -54,6 +55,8 @@ public :
 	// Close the file.
 	void close();
 
+	std::string getErrorMessage() const;
+
 	// Get the current position in the file.
 	size_t pos();
 
@@ -103,6 +106,9 @@ public :
 private :
 
 	FILE *m_handle;
+
+	// Error
+	mutable std::error_condition m_error;
 };
 
 } //namespace sp