In the following example:

std::vector <int> squares;
squares.push_back(1);
squares.push_back(4);
squares.push_back(9);
squares.push_back(16);

std::map <std::string, int> ages;
ages["Daniel"] = 26;
ages["Jesse"] = 24;
out << ages;

YAML::Emitter out;
out << YAML::BeginSeq;
out << YAML::Flow << squares;
out << ages;
out << YAML::EndSeq;

You need to remove the 1st "out << ages;" for it to make sense with the output.

Good catch!

How should one emit a UTF-8-coded text? I recieve only "\xffffffd0\ffffffa7..."

@fromagxo, it's currently not implemented. I'll get to it... (soon?)

Is there a way to write out a NULL value? For instance:

out << YAML::BeginMap;
out << YAML::Key << "version" << YAML::Value << 1;
out << YAML::Key << "optional" << YAML::Value << YAML::Null; // here
out << YAML::Key << "name" << YAML::Value << "my name";

There is now :)

Your syntax should work fine now (it'll produce "~", the canonical null value). The reason I didn't previously implement it is that parsing empty doesn't work properly. I opened up  Issue 28 , if you're interested in following along.

Is there a way to update a node in an existing document? Or do you need to rewrite the whole document?

Currently, there's no way to modify an existing node. There may be one in the future, but I'm not sure.

Hi, first of all, thanks for all your work, YAML is awesome!

I stumbled across a problem while trying to emit empty lists and maps, for example it should be possible to have something like this in a YAML document:

emptyList: []
emptyMap: {}

This way, you already know that it's a sequence or a map, but currently, it's empty. However, when I emit YAML::BeginSeq directly followed by YAML::EndSeq, it gives me the following exception: src/emitter.cpp:348: void YAML::Emitter::EmitEndSeq(): Assertion curState == ES_DONE_WITH_BLOCK_SEQ_ENTRY' failed. The same happens for empty maps. And I wouldn't like to add ~ as an entry to the list as a workaround.

Thanks!

Oh, I already found what I was looking for: empty sequences or maps must be flowing, not blocky. But maybe you could automatically emit a flow-style sequence or map when it's empty?

Hi Micha,

Good idea! It's fixed (see  issue 51 ).

Hello, I'm finding it very hard to modify YAML documents.

I would like to parse a document and then add or remove nodes to it. I don't mind if I have to create a new document that's based on an old one, but it doesn't seem like the library provides much functionality for composing documents together or modifying documents.

Any help or documentation on how this can currently be achieved? Ie. how to use the Emitter to emit two nodes?

Thanks.

@kranar, there's unfortunately not a great way of doing this. I added a little explanation of how to use the current functionality. Does this help?

Thanks for the help. I did something similar to this to achieve what I wanted.

If i do :

~YAML::Emitter out;
out << YAML::BeginSeq;
out << YAML::BeginMap;
out << YAML::Key << "name" << YAML::Value << "Fred";
out << YAML::Key << "age" << YAML::Value << "42";
out << YAML::EndMap;
out << YAML::BeginMap;
out << YAML::Key << "name" << YAML::Value << "John";
out << YAML::Key << "age" << YAML::Value << "43";
out << YAML::EndMap;
out << YAML::EndSeq;

It produces:

-
  name:Fred
  age:42
-
  name:John
  age:42

How can I prodeuce this:

- name:Fred
  age:42
- name:John
  age:42

Thanks

@ze.p.smarques

Currently, there's no way. I've been thinking about how to effectively do that, and I haven't come up with a nice way. But it's going to happen somewhere down the road, I hope.

OK, thanks for the info.

I hope you do implement that, it would be awesome.

thanks

@ze.p.smarques, if you're interested in following along, it's  Issue 61 . I don't know when I'll get to it, though, but you can follow it and get an update when I do.

Hi,

is there a way to directly pass the output to an std::ostream (e.g. ofstream)?

e.g.

ofstream ofstr("output.yaml");
YAML::Emitter out(ofstr);
out << some_large_document;

// not necessary anymore:
// ofstr << out.c_str()

I guess it would speed up the process, especially on large files, if the output isn't fully cached in memory...

Thanks

@baeuml.kit

Not yet, but there will be. I plan to refactor the emitter soon, and I'm going to add hooks to directly output to an std::ostream or a YAML::Node.

@ze.p.smarques

I faced the same issue; a simple patch (0.2.4 sources or SVN) did the job for me:

In emitter.cpp change the function to:

// EmitBeginMap
void Emitter::EmitBeginMap()
{
    if(!good())
        return;

    // must have a long key if we're emitting a map
    m_pState->StartLongKey();

    PreAtomicWrite();

    EMITTER_STATE curState = m_pState->GetCurState();
    EMITTER_MANIP flowType = m_pState->GetFlowType(GT_MAP);
    if(flowType == Block) {
        if(curState == ES_WRITING_BLOCK_SEQ_ENTRY || curState == ES_WRITING_BLOCK_MAP_KEY || curState == ES_WRITING_BLOCK_MAP_VALUE) {
            if(curState != ES_WRITING_BLOCK_SEQ_ENTRY) // <----- Added!! ----->
                m_stream << "\n";
            m_pState->UnsetSeparation();
        }
        m_pState->PushState(ES_WAITING_FOR_BLOCK_MAP_ENTRY);
    } else if(flowType == Flow) {
        EmitSeparationIfNecessary();
        m_stream << "{";
        m_pState->PushState(ES_WAITING_FOR_FLOW_MAP_ENTRY);
    } else
        assert(false);

    m_pState->BeginGroup(GT_MAP);
}

Works (for me) as supposed:

- filename: /export0/20091127.stream
  writer-class: stream::writer_simple
  reader-class: stream::reader_simple
  typefactory:
    - compound-name: order
      definition:
        - name: id
          type: uint64_t
        - name: security
          type: uint32_t
        - name: volume
          type: uint32_t
        - name: value
          type: double
...
...

Hi. I've got a situation here... Just trying to feed your aliases-examlples to parsing. And I have a YAML::ParserException?? at GetNextDocument??(doc). Emitter produces correct output and fails on it's way back. (The commented code with a NULL works fine).

YAML::Emitter out;
out << YAML::BeginSeq;
out << YAML::Anchor("fred");
out << YAML::BeginMap;
out << YAML::Key << "name" << YAML::Value << "Fred";
out << YAML::Key << "age" << YAML::Value << 42;
out << YAML::EndMap;
out << YAML::Alias("fred");
out << YAML::EndSeq;
/*out << YAML::BeginSeq;
out << YAML::Anchor("fred") << YAML::Null;
out << YAML::Alias("fred");
out << YAML::EndSeq;*/
		

cout << "Here's the output YAML:\n" << out.c_str()<<endl;
std::stringstream stream(out.c_str());
YAML::Parser parser(stream);
YAML::Node doc;
parser.GetNextDocument(doc);

@Maestro,

I can't reproduce your error. I copied and pasted your code exactly and it worked. What version are you using, what compiler, what OS, etc.?

By the way, in the future, please post questions on http://stackoverflow.com and tag them as yaml-cpp.

@jbeder, I use msvc2008. XP64 and XP32 at work. The error is the same. I tried msvc2005 too with a lib built from project files provided in your FAQ section. The result is the same. I doubt it's about system. I just did a run through debug, and I can say that it successfully detects sequence and founds anchor, saves anchor step

if(m_pContent)
m_pContent->Parse(pScanner, state);

is skipped, and then in Sequence ParseBlock?() I have an exception at

if(token.type != Token::BLOCK_ENTRY && token.type != Token::BLOCK_SEQ_END)
				throw ParserException(token.mark, ErrorMsg::END_OF_SEQ);

Any suggestions? What happened to MAP-part parsing? Oh, I use 2.4. Just noticed that 2.5 is already available. I'll try it tomorrow.

@Maestro,

I just confirmed that this is indeed a bug in 0.2.4, but it's been fixed in 0.2.5.

@jbeder Yes, 0.2.5. passes the test. Thanks. Next time I'll need help I try that stackoverflow.com thing, do you check it on regular basis too?

@Maestro, absolutely, and I'm subscribed to the RSS feed for the tag yaml-cpp.

I was built your library on VS 2008 and included static library to my project. After starting application i got an exception when using

inline Emitter& operator << (Emitter& emitter, const char v) { return emitter.Write(std::string(v)); }

function

my method receive char* param .

YAML::Emitter emitter; 
emitter << YAML::BeginMap; 
emitter << YAML::Key << "param"; 
emitter << YAML::Value << param;

@sergey

1. What exception? 2. Is ‘param‘ null? 3. Please read the front page - post questions on stackoverflow.com

Hi

It says

error: no match for ‘operator==’ in ‘it.YAML::Iterator::first() == "foo"’

when I run the code in http://code.google.com/p/yaml-cpp/wiki/HowToEmitYAML#Using_Existing_Nodes

YAML::Node node; // suppose this is a parsed map of scalars to scalars

// and we want to replace the value of the key "foo" with "bar"

emitter << YAML::Key << it.first(); emitter << YAML::Value; if(it.first() == "foo")

emitter << "bar";

else

emitter << it.second();

How can I check if the current node is the "foo"?

Thanks in advance

Srimal.

@srimal, sorry, I forgot to update that with the removal of operator == on Nodes. Instead, use

if(it.first().to<std::string>() == "foo") { ... }

I small typo in the example: out << YAML::BeginSeq? << v.x << v.y << v.z << YAML:EndSeq?; the last : should be ::

@tomvd, thanks, corrected!

How can I emit the following?

# Food
- eggs
- cereals

# Drinks
- water
- coffee

I tried this:

YAML::Emitter out;
out << YAML::Comment("Food");
out << YAML::BeginSeq;
out << "eggs";
out << "cereals";
out << YAML::EndSeq;
out << YAML::Comment("Drinks");
out << YAML::BeginSeq;
out << "water";
out << "coffee";
out << YAML::EndSeq;

But that doesn't work. I found that creating multiple emmiters works tho:

std::string buffer;
{
YAML::Emitter out;
out << YAML::Comment("Food");
out << YAML::BeginSeq;
out << "eggs";
out << "cereals";
out << YAML::EndSeq;
buffer += out.c_str() + "\n";
}
{
YAML::Emitter out;
out << YAML::Comment("Drinks");
out << YAML::BeginSeq;
out << "water";
out << "coffee";
out << YAML::EndSeq;
buffer += out.c_str();
}

Is this really the only way?

@philippe:

YAML::Emitter out;
out << YAML::Comment("Food");
out << YAML::BeginSeq;
out << "eggs" << "cereals";
out << YAML::Newline << YAML::Newline;
out << YAML::Comment("Drinks");
out << "water" << "coffee";
out << YAML::EndSeq;
std::cout << out.c_str() << "\n";

(Note you need two newlines because the first moves it to the next line, and the second creates the blank space.)

By the way, in the future, please ask questions like this on stackoverflow.com.

Thanks! Btw, the bug with maps in a sequence that adds an additional newline is kinda annoying (see ze.p.sma...@gmail.com post from Dec 2, 2009). Is it fixed on trunk? Atm I fixed it by editing the source.

@philippe, yes that's fixed - it should even be in the 0.2.7 release.

It's not fixed in 0.2.7... see http://ideone.com/6Ok0L

@philippe, interesting. I filed that as a new bug,  Issue 135 . You said that you fixed it by editing the source; how did you fix this one? (If you like, please comment on the issue itself.)

Thanks!

I just commented the line inserting a new line in emmiter.cpp. This very likely broke something else, but for my use case "it works". I'm not sure what the right approach would be, but probably that you'd have to fiddle with m_pState->RequiresHardSeparation?().