diff -r 0a40752e401d -r 40ab091e5dfa src/types/StringDataTypeWriter.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/types/StringDataTypeWriter.h	Sat Jul 21 19:04:37 2018 +0200
@@ -0,0 +1,46 @@
+#pragma once
+
+#include <string>
+#include <sstream>
+#include <iostream>
+#include <vector>
+#include <locale>
+#include <codecvt>
+
+#include "../DataTypeWriter.h"
+#include "../format.h"
+
+namespace relpipe {
+namespace writer {
+namespace types {
+
+using namespace relpipe::writer;
+/**
+ * The prototype does not recognize any encoding,
+ * it just works with c++ strings in encoding default to given platform. 
+ * In the real implementation of relational pipes, there will be DataTypes for particular encodings.
+ */
+class StringDataTypeWriter : public DataTypeWriter<string_t> {
+private:
+	IntegerDataTypeWriter integerType;
+	std::wstring_convert<std::codecvt_utf8<wchar_t>> convertor; // TODO: support also other encodings.
+public:
+
+	StringDataTypeWriter() : DataTypeWriter<string_t>(DATA_TYPE_ID_STRING, DATA_TYPE_CODE_STRING) {
+	}
+
+	void writeValue(std::ostream &output, const string_t &value) override {
+		std::string s = convertor.to_bytes(value);
+		integerType.writeValue(output, s.length());
+		output << s.c_str();
+	}
+
+	wstring toValue(const string_t &stringValue) override {
+		return stringValue;
+	}
+
+};
+
+}
+}
+}
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