Q: Emitting JSON with yaml-cpp? I'm using yaml-cpp on a for a variety of things on my project.  Now I want to write out some data as JSON.  Since JSON is a subset of YAML, at least for the features I need, I understand it should be possible to set some options in yaml-cpp to output pure JSON.  How is that done?

A: yaml-cpp doesn't directly have a way to force JSON-compatible output, but you can probably emulate it.
YAML:Emitter Emitter;
emitter << YAML:: DoubleQuoted << YAML::Flow << /* rest of code */;


A: Jesse Beder's answer didn't seem to work for me; I still got multiple lines of output with YAML syntax. However, I found that by adding << YAML::BeginSeq immediately after << YAML::Flow, you can force everything to end up on one line with JSON syntax. You then have to remove the beginning [ character:
YAML::Emitter emitter;
emitter << YAML::DoubleQuoted << YAML::Flow << YAML::BeginSeq << node;
std::string json(emitter.c_str() + 1);  // Remove beginning [ character

Here is a fully worked example.
There's still a major issue, though: numbers are quoted, turning them into strings. I'm not sure whether this is an intentional behavior of YAML::DoubleQuoted; looking at the tests, I didn't see any test case that covers what happens when you apply DoubleQuoted to a number. This issue has been filed here.
