How can I add string pairs to a document of rapidjson

Question

I want to create a json string using rapidjson. But I got a error: unable to convert std::string to rapidjson::Type.

int x = 111;
string className = "myclass";

Document doc;
auto& allocator = doc.GetAllocator();

doc.AddMember("x", Value().SetInt(x), allocator);
doc.AddMember("className", className, allocator);

unordered_map<string, string>& map = sprite->toMap();
for (const auto& pair : map) {
    Value key(pair.first.c_str(), pair.first.size(), allocator);
    doc.AddMember(key, pair.second, allocator);
}

StringBuffer sb;
Writer<StringBuffer> writer(sb);

doc.Accept(writer);
log("json string: %s", sb.GetString());

Milo Yip · Accepted Answer · 2016-01-04T09:36:50.803

If #define RAPIDJSON_HAS_STDSTRING 1 (before including rapidjson header files, or defined in compiling flags), there are some extra APIs for std::string.

To make "copy-strings" (allocated duplicates of source strings) of std::string, you can use constructor with allocator:

for (auto& pair : map) {
    rapidjson::Value key(pair.first, allocator);
    rapidjson::Value value(pair.second, allocator);
    doc.AddMember(key, value, allocator);
}

Or make it a single statement:

for (auto& pair : map)
    doc.AddMember(
        rapidjson::Value(pair.first, allocator).Move(),
        rapidjson::Value(pair.second, allocator).Move(),
        allocator);

If you presume that the lifetime of strings are longer than doc, then you can use "const-string" instead, which is simpler and more efficient:

for (auto& pair : map)
    doc.AddMember(
        rapidjson::StringRef(pair.first),
        rapidjson::StringRef(pair.second),
        allocator);

I think the macro RAPIDJSON_HAS_STDSTRING should be documented better...

The #define RAPIDJSON_HAS_STDSTRING 1 ! – waas1919 Jul 22 '17 at 15:54 — waas1919, Jul 22 '17 at 15:54

Zen · Answer 2 · 2016-01-03T08:28:13.810

Now, I realise that I have made 2 mistake:
1. I should invoke doc.SetObject(); after doc is created.
2. How to create string in rapidjson.

Document doc;
doc.SetObject();
auto& allocator = doc.GetAllocator();

rapidjson::Value s;
s = StringRef(className.c_str());
doc.AddMember("className", s, allocator);

auto& map = sprite->toJson();
for (auto& pair : map) {
    rapidjson::Value key(pair.first.c_str(), pair.first.size(), allocator);
    rapidjson::Value value(pair.second.c_str(), pair.second.size(), allocator);
    doc.AddMember(key, value, allocator);
}

There should be some better way to do it.

How can I add string pairs to a document of rapidjson

2 Answers2