How to use yaml-cpp in a C++ program on Linux?

Question

I have recently decided to use yaml as my configuration file technology, and am writing a c++ linux application on OpenSuse 11.3.

The problem is that even after successfully installing cmake, compilling yaml-cpp as shown on the yaml-cpp docs page, I still can't compile the simple demo programs on the yaml-cpp page here.

For example, when I try to compile the the monster.yaml and main.cpp example

my compiler on issuing the command gcc main.cpp, it issues the following errors:

main.cpp:24:25: error: ‘YAML’ does not name a type
main.cpp:24:35: error: expected unqualified-id before ‘&’ token
main.cpp:24:35: error: expected ‘)’ before ‘&’ token
main.cpp:24:35: error: expected initializer before ‘&’ token
main.cpp:30:25: error: ‘YAML’ does not name a type
main.cpp:30:35: error: expected unqualified-id before ‘&’ token
main.cpp:30:35: error: expected ‘)’ before ‘&’ token
main.cpp:30:35: error: expected initializer before ‘&’ token
main.cpp:35:25: error: ‘YAML’ does not name a type
main.cpp:35:35: error: expected unqualified-id before ‘&’ token
main.cpp:35:35: error: expected ‘)’ before ‘&’ token
main.cpp:35:35: error: expected initializer before ‘&’ token

I tried changing the include directive from #include "yaml-cpp/yaml.h" to #include <yaml.h>, since I'd installed the yaml lib, but this didn't solve anything.

so what did I do wrong?

Here is the problematic code pasted from lines 24 to 40:

void operator >> (const YAML::Node& node, Vec3& v) {
   node[0] >> v.x;
   node[1] >> v.y;
   node[2] >> v.z;
}

void operator >> (const YAML::Node& node, Power& power) {
   node["name"] >> power.name;
   node["damage"] >> power.damage;
}

void operator >> (const YAML::Node& node, Monster& monster) {
   node["name"] >> monster.name;
   node["position"] >> monster.position;
   const YAML::Node& powers = node["powers"];
   for(unsigned i=0;i<powers.size();i++) {
      Power power;
      powers[i] >> power;
      monster.powers.push_back(power);
   }
}

And here is a dump of the output of the sudo make install after I run the make command:

[ 81%] Built target yaml-cpp
[ 96%] Built target run-tests
[100%] Built target parse
Install the project...
-- Install configuration:      "Release"                                                                                                                                              
-- Installing: /usr/local/lib/libyaml-cpp.so.0.2.6
-- Up-to-date: /usr/local/lib/libyaml-cpp.so.0.2
-- Up-to-date: /usr/local/lib/libyaml-cpp.so
-- Up-to-date: /usr/local/include/yaml-cpp/aliasmanager.h
-- Up-to-date: /usr/local/include/yaml-cpp/anchor.h
-- Up-to-date: /usr/local/include/yaml-cpp/conversion.h
-- Up-to-date: /usr/local/include/yaml-cpp/dll.h
-- Up-to-date: /usr/local/include/yaml-cpp/emitfromevents.h
-- Up-to-date: /usr/local/include/yaml-cpp/emitter.h
-- Up-to-date: /usr/local/include/yaml-cpp/emittermanip.h
-- Up-to-date: /usr/local/include/yaml-cpp/eventhandler.h
-- Up-to-date: /usr/local/include/yaml-cpp/exceptions.h
-- Up-to-date: /usr/local/include/yaml-cpp/iterator.h
-- Up-to-date: /usr/local/include/yaml-cpp/ltnode.h
-- Up-to-date: /usr/local/include/yaml-cpp/mark.h
-- Up-to-date: /usr/local/include/yaml-cpp/node.h
-- Up-to-date: /usr/local/include/yaml-cpp/nodeimpl.h
-- Up-to-date: /usr/local/include/yaml-cpp/nodereadimpl.h
-- Up-to-date: /usr/local/include/yaml-cpp/nodeutil.h
-- Up-to-date: /usr/local/include/yaml-cpp/noncopyable.h
-- Up-to-date: /usr/local/include/yaml-cpp/null.h
-- Up-to-date: /usr/local/include/yaml-cpp/ostream.h
-- Up-to-date: /usr/local/include/yaml-cpp/parser.h
-- Up-to-date: /usr/local/include/yaml-cpp/stlemitter.h
-- Up-to-date: /usr/local/include/yaml-cpp/stlnode.h
-- Up-to-date: /usr/local/include/yaml-cpp/traits.h
-- Up-to-date: /usr/local/include/yaml-cpp/yaml.h
-- Up-to-date: /usr/local/include/yaml-cpp/anchordict.h
-- Up-to-date: /usr/local/include/yaml-cpp/graphbuilder.h
-- Installing: /usr/local/lib/pkgconfig/yaml-cpp.pc

Could there probably be some special directive / option that I have to append to the gcc command when compiling with libyaml? something like gcc main.cpp -libyaml ?

For more output from the compiler (gcc version 4.5.0 20100604 [gcc-4_5-branch revision 160292] (SUSE Linux)) :

/tmp/ccYltArL.o: In function `operator>>(YAML::Node const&, Monster&)':
main.cpp:(.text+0x1a8): undefined reference to `YAML::Node::size() const'
/tmp/ccYltArL.o: In function `main':
main.cpp:(.text+0x1fe): undefined reference to `std::basic_ifstream<char,      std::char_traits<char> >::basic_ifstream(char const*, std::_Ios_Openmode)'
main.cpp:(.text+0x215): undefined reference to   `YAML::Parser::Parser(std::basic_istream<char, std::char_traits<char> >&)'
main.cpp:(.text+0x224): undefined reference to `YAML::Node::Node()'
main.cpp:(.text+0x23e): undefined reference to    `YAML::Parser::GetNextDocument(YAML::Node&)'
main.cpp:(.text+0x29c): undefined reference to `std::cout'

and much more stuff than can fit here , finally ending in:

/tmp/ccYltArL.o:(.rodata._ZTIN4YAML14BadDereferenceE[typeinfo for YAML::BadDereference]+0x0): undefined reference to `vtable for    __cxxabiv1::__si_class_type_info'
/tmp/ccYltArL.o:(.rodata._ZTIN4YAML11KeyNotFoundE[typeinfo for YAML::KeyNotFound]+0x0): undefined reference to `vtable for  __cxxabiv1::__si_class_type_info'
/tmp/ccYltArL.o:(.rodata._ZTIN4YAML13InvalidScalarE[typeinfo for YAML::InvalidScalar]+0x0): more undefined references to `vtable for __cxxabiv1::__si_class_type_info' follow
/tmp/ccYltArL.o:(.rodata._ZTIN4YAML9ExceptionE[typeinfo for YAML::Exception]+0x8): undefined reference to `typeinfo for std::runtime_error'
/tmp/ccYltArL.o:(.eh_frame+0x18f): undefined reference to `__gxx_personality_v0'
collect2: ld returned 1 exit status

-- finally --

Solved it with Chris's soln (see below), though I actually found an even cleaner way of pre-loading 'custom' libraries, by using the ldconfig command to configure the library search path after i add the path to my libs into a *.conf file in /etc/ld.so.conf.d/. See the detailed guide here...

Answer 1

gcc isn't being instructed to look in /usr/local. You need to do it explicitly. Also, that really should be g++ and not gcc. So first make sure your include looks like this:

#include "yaml-cpp/yaml.h"

Then compile it like this:

g++ -I/usr/local/include -L/usr/local/lib -lyaml-cpp -o testprogram main.cpp