revert unwise data structure change

include/xlnt/workbook/workbook.hpp

@@ -26,6 +26,7 @@
 
 #include <functional>
 #include <iterator>
+#include <map>
 #include <memory>
 #include <string>
 #include <unordered_map>
@@ -760,15 +761,15 @@ public:
     /// </summary>
     std::size_t add_shared_string(const rich_text &shared, bool allow_duplicates = false);
 
-  	/// <summary>
-  	/// Returns a reference to the shared string ordered by id
-  	/// </summary>
-  	const std::unordered_map<std::size_t, rich_text> &shared_strings_by_id() const;
+    /// <summary>
+    /// Returns a reference to the shared string ordered by id
+    /// </summary>
+    const std::map<std::size_t, rich_text> &shared_strings_by_id() const;
 
-  	/// <summary>
-  	/// Returns a reference to the shared string related to the specified index
-  	/// </summary>
-  	const rich_text &shared_strings(std::size_t index) const;
+    /// <summary>
+    /// Returns a reference to the shared string related to the specified index
+    /// </summary>
+    const rich_text &shared_strings(std::size_t index) const;
 
     /// <summary>
     /// Returns a reference to the shared strings being used by cells

source/detail/implementations/workbook_impl.hpp

@@ -118,7 +118,7 @@ struct workbook_impl
 
     std::list<worksheet_impl> worksheets_;
     std::unordered_map<rich_text, std::size_t, rich_text_hash> shared_strings_ids_;
-    std::unordered_map<std::size_t, rich_text> shared_strings_values_;
+    std::map<std::size_t, rich_text> shared_strings_values_;
 
     optional<stylesheet> stylesheet_;
 

source/workbook/workbook.cpp

@@ -1332,7 +1332,7 @@ const manifest &workbook::manifest() const
     return d_->manifest_;
 }
 
-const std::unordered_map<std::size_t, rich_text> &workbook::shared_strings_by_id() const
+const std::map<std::size_t, rich_text> &workbook::shared_strings_by_id() const
 {
     return d_->shared_strings_values_;
 }