[C++] Use Json shortcuts so US_ASCII can be encoded and UTF-8 in shortest format.

Author: mjpt777

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/cpp/CppGenerator.java

@@ -529,14 +529,25 @@ private CharSequence generateVarData(final String className, final List<Token> t
  indent + " std::string s = get%1$sAsString();\n\n" +
  indent + " for (auto c = s.cbegin(); c != s.cend(); c++)\n" +
  indent + " {\n" +
- indent + " if (*c == '\"' || *c == '\\\\' || ('\\x00' <= *c && *c <= '\\x1f'))\n" +
+ indent + " switch (*c)\n" +
  indent + " {\n" +
- indent + " oss << \"\\\\u\"" + " << std::hex << std::setw(4)\n" +
- indent + " << std::setfill('0') << (int)(*c);\n" +
- indent + " }\n" +
- indent + " else\n" +
- indent + " {\n" +
- indent + " oss << *c;\n" +
+ indent + " case '\"': oss << \"\\\\\\\"\"; break;\n" +
+ indent + " case '\\\\': oss << \"\\\\\\\\\"; break;\n" +
+ indent + " case '\\b': oss << \"\\\\b\"; break;\n" +
+ indent + " case '\\f': oss << \"\\\\f\"; break;\n" +
+ indent + " case '\\n': oss << \"\\\\n\"; break;\n" +
+ indent + " case '\\r': oss << \"\\\\r\"; break;\n" +
+ indent + " case '\\t': oss << \"\\\\t\"; break;\n\n" +
+ indent + " default:\n" +
+ indent + " if ('\\x00' <= *c && *c <= '\\x1f')\n" +
+ indent + " {\n" +
+ indent + " oss << \"\\\\u\"" + " << std::hex << std::setw(4)\n" +
+ indent + " << std::setfill('0') << (int)(*c);\n" +
+ indent + " }\n" +
+ indent + " else\n" +
+ indent + " {\n" +
+ indent + " oss << *c;\n" +
+ indent + " }\n" +
  indent + " }\n" +
  indent + " }\n\n" +
  indent + " return oss.str();\n" +