Compilation of the Hello Example doesn't work or something?

[jimisdam]

I followed the steps for compiling the source and when I compile the example hello, I get this:

> ➜  hello g++ -std=c++11 -I ../../include -I ../../deps -I ../../deps/include -I ../../include/sleepy_discord/IncludeNonexistent example0.cpp -L../../buildtools -L/usr/lib -lsleepy_discord -lcurl -lssl -lcrypto -lpthread -o example.out
../../buildtools/libsleepy_discord.a(client.o): In function `SleepyDiscord::CPRSession::setUrl(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)':
client.cpp:(.text._ZN13SleepyDiscord10CPRSession6setUrlERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE[_ZN13SleepyDiscord10CPRSession6setUrlERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE]+0x37): undefined reference to `cpr::Session::SetUrl(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
../../buildtools/libsleepy_discord.a(client.o): In function `SleepyDiscord::CPRSession::setBody(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const*)':
client.cpp:(.text._ZN13SleepyDiscord10CPRSession7setBodyEPKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE[_ZN13SleepyDiscord10CPRSession7setBodyEPKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE]+0x37): undefined reference to `cpr::Session::SetBody(cpr::Body&&)'
../../buildtools/libsleepy_discord.a(client.o): In function `SleepyDiscord::CPRSession::Post()':
client.cpp:(.text._ZN13SleepyDiscord10CPRSession4PostEv[_ZN13SleepyDiscord10CPRSession4PostEv]+0x33): undefined reference to `cpr::Session::Post()'
../../buildtools/libsleepy_discord.a(client.o): In function `SleepyDiscord::CPRSession::Patch()':
client.cpp:(.text._ZN13SleepyDiscord10CPRSession5PatchEv[_ZN13SleepyDiscord10CPRSession5PatchEv]+0x33): undefined reference to `cpr::Session::Patch()'
../../buildtools/libsleepy_discord.a(client.o): In function `SleepyDiscord::CPRSession::Delete()':
client.cpp:(.text._ZN13SleepyDiscord10CPRSession6DeleteEv[_ZN13SleepyDiscord10CPRSession6DeleteEv]+0x33): undefined reference to `cpr::Session::Delete()'
../../buildtools/libsleepy_discord.a(client.o): In function `SleepyDiscord::CPRSession::Get()':
client.cpp:(.text._ZN13SleepyDiscord10CPRSession3GetEv[_ZN13SleepyDiscord10CPRSession3GetEv]+0x33): undefined reference to `cpr::Session::Get()'
../../buildtools/libsleepy_discord.a(client.o): In function `SleepyDiscord::CPRSession::Put()':
client.cpp:(.text._ZN13SleepyDiscord10CPRSession3PutEv[_ZN13SleepyDiscord10CPRSession3PutEv]+0x33): undefined reference to `cpr::Session::Put()'
../../buildtools/libsleepy_discord.a(client.o): In function `SleepyDiscord::CPRSession::CPRSession()':
client.cpp:(.text._ZN13SleepyDiscord10CPRSessionC2Ev[_ZN13SleepyDiscord10CPRSessionC5Ev]+0x33): undefined reference to `cpr::Session::Session()'
client.cpp:(.text._ZN13SleepyDiscord10CPRSessionC2Ev[_ZN13SleepyDiscord10CPRSessionC5Ev]+0x5a): undefined reference to `cpr::Multipart::Multipart(std::initializer_list<cpr::Part> const&)'
client.cpp:(.text._ZN13SleepyDiscord10CPRSessionC2Ev[_ZN13SleepyDiscord10CPRSessionC5Ev]+0xa6): undefined reference to `cpr::Session::~Session()'
../../buildtools/libsleepy_discord.a(client.o): In function `SleepyDiscord::CPRSession::~CPRSession()':
client.cpp:(.text._ZN13SleepyDiscord10CPRSessionD2Ev[_ZN13SleepyDiscord10CPRSessionD5Ev]+0x34): undefined reference to `cpr::Session::~Session()'
../../buildtools/libsleepy_discord.a(cpr_session.o): In function `SleepyDiscord::CPRSession::setHeader(std::vector<SleepyDiscord::HeaderPair, std::allocator<SleepyDiscord::HeaderPair> > const&)':
cpr_session.cpp:(.text+0x11e): undefined reference to `cpr::Session::SetHeader(std::map<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, cpr::CaseInsensitiveCompare, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > > const&)'
../../buildtools/libsleepy_discord.a(cpr_session.o): In function `SleepyDiscord::CPRSession::setMultipart(std::initializer_list<SleepyDiscord::Part> const&)':
cpr_session.cpp:(.text+0x35d): undefined reference to `cpr::Session::SetMultipart(cpr::Multipart const&)'
../../buildtools/libsleepy_discord.a(cpr_session.o): In function `std::_Rb_tree<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::_Select1st<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, cpr::CaseInsensitiveCompare, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >::_M_get_insert_unique_pos(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)':
cpr_session.cpp:(.text._ZNSt8_Rb_treeINSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEESt4pairIKS5_S5_ESt10_Select1stIS8_EN3cpr22CaseInsensitiveCompareESaIS8_EE24_M_get_insert_unique_posERS7_[_ZNSt8_Rb_treeINSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEESt4pairIKS5_S5_ESt10_Select1stIS8_EN3cpr22CaseInsensitiveCompareESaIS8_EE24_M_get_insert_unique_posERS7_]+0x64): undefined reference to `cpr::CaseInsensitiveCompare::operator()(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) const'
cpr_session.cpp:(.text._ZNSt8_Rb_treeINSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEESt4pairIKS5_S5_ESt10_Select1stIS8_EN3cpr22CaseInsensitiveCompareESaIS8_EE24_M_get_insert_unique_posERS7_[_ZNSt8_Rb_treeINSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEESt4pairIKS5_S5_ESt10_Select1stIS8_EN3cpr22CaseInsensitiveCompareESaIS8_EE24_M_get_insert_unique_posERS7_]+0x11f): undefined reference to `cpr::CaseInsensitiveCompare::operator()(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) const'
../../buildtools/libsleepy_discord.a(cpr_session.o): In function `std::_Rb_tree_iterator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > std::_Rb_tree<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::_Select1st<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, cpr::CaseInsensitiveCompare, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >::_M_insert_<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::_Rb_tree<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::_Select1st<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, cpr::CaseInsensitiveCompare, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >::_Alloc_node>(std::_Rb_tree_node_base*, std::_Rb_tree_node_base*, std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >&&, std::_Rb_tree<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::_Select1st<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, cpr::CaseInsensitiveCompare, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >::_Alloc_node&)':
cpr_session.cpp:(.text._ZNSt8_Rb_treeINSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEESt4pairIKS5_S5_ESt10_Select1stIS8_EN3cpr22CaseInsensitiveCompareESaIS8_EE10_M_insert_IS8_NSE_11_Alloc_nodeEEESt17_Rb_tree_iteratorIS8_EPSt18_Rb_tree_node_baseSK_OT_RT0_[_ZNSt8_Rb_treeINSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEESt4pairIKS5_S5_ESt10_Select1stIS8_EN3cpr22CaseInsensitiveCompareESaIS8_EE10_M_insert_IS8_NSE_11_Alloc_nodeEEESt17_Rb_tree_iteratorIS8_EPSt18_Rb_tree_node_baseSK_OT_RT0_]+0x68): undefined reference to `cpr::CaseInsensitiveCompare::operator()(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) const'
collect2: error: ld returned 1 exit status

What's wrong with it? I'm using Fedora 28.

[yourWaifu]

It looks like you didn't link cpr, compile it and link (adding ../../deps/cpr/cpr/*.cpp should also work).

[jimisdam]

Thank you a lot, it worked! But, why would this happen, even following the given steps?

[yourWaifu]

Here how I understand it. take a look at this code.

void exampleFunction();

int main() {
    exampleFunction();
}

Although, this is valid code if exampleFunction is defined later. However, afterwards the linker will look for the definition of exampleFunction and not find it so it gives an similar to what you see above. Fixing this is very simple.

void exampleFunction();

int main() {
    exampleFunction();
}

void exampleFunction() {
    int a = 4;
    a = 3;
}