undefined reference error when building program using shared library that link static library

See also questions close to this topic

• Trouble finding output in ARMsim

  Hi I'm currently working on a project and I feel dumb for not knowing this, but I'm having trouble seeing some outputs in my code. I've attached an image of what I'm seeing below and I've checked the console, stdout, and watchView and nothing is showing. Is there something I didn't include in my code or something I'm overlooking?

  Edit: I realize it might be important to say that my end goal is to analyze the integers in integer.dat and look at stuff like the total number of integers in the file and any number of occurrences of the same integer(if any)

  .equ SWI_Open, 0x66 @open file
  .equ SWI_Close,0x68 @ close file
  .equ SWI_PrChr,0x00 @display an ascii char to stdout
  .equ SWI_PrStr,0x69 @write string to file or stdout
  .equ SWI_PrInt,0x6b @write an integer to file
  
  .equ SWI_RdInt,0x6c @read an integer from a fike
  .equ Stdout,1 @set output goal to be stdout
  .equ SWI_Exit, 0x11 @prevent execution
  
  .global_start:
  .text
  
  
  
  @print an preliminary message to the screen
  mov R0,#Stdout @print an initial message
  ldr R1, = Message1 @load cope with of message1 label
  swi SWI_PrStr @display message to stdout
  
  
  @------------open file----------
  ldr r0, = integerFile  @set call for input document
  mov r1,#0       @mode is input
  swi SWI_Open @open record for input
  bcs InFileError @check bring-bit(C): if =1 then error
  
  
  @--------file error handling------------
  InFileError:
  mov R0,#Stdout
  ldr R1, = errMsg
  swi SWI_PrStr
  
  
  
  integerFile: .asciz "input.dat"
  errMsg: .asciz "failed to open input.dia"
  Message1: .asciz "Hello\n"
  

  
• Does this statement turn into a nop?

  I am wondering if the code below, when the line #define PRINT_STATEMENT is commented out, will take many CPU cycles to execute on an ARM microcontroller:

  #define PRINT_STATEMENT       1
  
  #if PRINT_STATEMENT
     #define PRINT_DBG(...)     printf(__VA_ARGS__)
  #else
     #define PRINT_DBG(...)
  #endif
  
  int main(){
     PRINT_DBG("Hello World\n");
     return 0;
  }
  

  I tested commenting out the #define PRINT_STATEMENT line on an online C compiler and can see that the print statement did not get executed. However, I am still wondering if the program were to be flashed onto an ARM microcontroller (with arm_gcc), will that line be turned into a nop operation?

  Thank you!
• Having trouble loading address in ARM

  Hi I'm doing a personal project in ARMsim. I am trying to open a document and display a message from the file but an error keeps appearing, "undefined symbol message1." Can anyone help?

  .equ SWI_Close,0x68 @ close a file 
  .equ SWI_PrChr,0x00 @write an ascii char to stdout
  .equ SWI_PrStr,0x69 @write a null-ending string
  .equ SWI_PrInt,0x6b @write an integer
  
  .equ SWI_RdInt,0x6c @read an integer from a fike
  .equ Stdout,1 @set output goal to be stdout
  .equ SWI_Exit, 0x11 @prevent execution
  
  .global_start:
  .text
  
  
  @print an preliminary message to the screen
  mov R0,#Stdout @print an initial message
  ldr R1, = Message1 @load cope with of message1 label
  swi SWI_PrStr @display message to stdout ```
  
• How to getStats() in WebRTC iOS SDK in Swift?

  I am trying to get ICE Candidate Pair Stats in iOS SDK in Swift. I see this specific interface: statsForTrack but I am unsure about how to use it. Has anybody done this before?
• What's the difference between Simulcast and SVC in WebRTC?

  After reading about Scalable Video Coding (SVC) and Simulcast on these links, I cannot tell what are the advantages of using one versus the other.

  So I am curious, what are the differences, pros, and cons between SVC and Simulcast?

  Does it make sense to use both techniques together?

  Thanks
• websocket client does not recieve event emitted from server

  I was trying to create video conferencing application where one user create offer and emit to signalling server and the signalling server will forward the data to another peer but the problem is when the peer 1(javascript client) emit OFFER event it reaches the server and it triggering the offer method on server and from server i will get data from peer 1 and emit the data to peer 2(javascript client) using sio.emit() but the peer 2 does not receiving OFFER event

  Client Code

      <script>
    var peersocket = null
    const socket = io("ws://localhost:8000?id={{ data['id'] }}")
    const my_per = document.getElementById("my_per") 
    const my_video = document.getElementById("my_video")
    const remote = document.getElementById("remote")
    const peer = new RTCPeerConnection();
    peer.addEventListener("track",function(e){
      console.log("track")
      remote.srcObject = e.streams[0]
    })
    console.log(navigator.mediaDevices)
    navigator.mediaDevices.getUserMedia({
      video:true,
      audio:true
    }).then(stream=>{
         my_video.srcObject = stream
         stream.getTracks().forEach(track=>{
           peer.addTrack(track,stream)
         })
         return
    }).then(_=>{
      socket.on("ANSWER",function(data){
        console.log("GOT ANSWER")
              peer.setRemoteDescription(data["answer"]).then(_=>{
                console.log("connected")
              })
      });
      socket.on("OFFER",function(data){
        console.log("GOT OFFER")
         peersocket = data["from"]
         peer.setRemoteDescription(data["offer"]).then(_=>{
             peer.createAnswer().then(answer=>{
               return peer.setLocalDescription(answer)
             }).then(_=>{
                 socket.emit("ANSWER",{
                    "to":peersocket,
                    "answer":peer.localDescription
                 })
             })
         })
        
      })
        socket.on("PEER_JOINED",function(data){
          console.log("PEER Joined")
          peersocket = data["sid"]
          peer.createOffer().then(offer=>{
            return peer.setLocalDescription(offer)
        }).then(_=>{
             return new Promise((resolve,reject)=>{
               console.log(peer)
                console.log("peer.iceConnectionState"+"[front Promise]")
                if  (peer.iceGatheringState == "complete"){
                      console.log("peer.iceConnectionState"+"[Promise]")
                      resolve()
                }else{
                    function statechange(e){
                        console.log(peer.iceGatheringState)
                        console.log("peer.iceConnectionState"+"[stateChange]")
                        if(peer.iceGatheringState == "complete"){
                            peer.removeEventListener("icegatheringstatechange",statechange)
                            resolve()
                        }
                    }
                    peer.addEventListener("icegatheringstatechange",statechange)
                }
             })
        }).then(_=>{
          console.log("EMITTING OFFER")
            socket.emit("OFFER",{
               "to":peersocket,
               "offer":peer.localDescription
            })
        })
        })
      
    }).catch(err=>{
      console.log(err)
    })
   
   
  
  </script>
  

  Peer 1 output

  PEER Joined
  EMITTING OFFER
  

  Peer 2 output

   no output in console
  

  Server code

  @sio.on('connect')
  async def connect(sid,env):
      interview_id = env["QUERY_STRING"].split("&")[0].split("=")[1]
      request = sio.get_environ(sid)['aiohttp.request']
      session = await get_session(request)
      user_id = session["id"]
      clients[user_id] = {
          "socket":sid,
          "interview_id":interview_id
      }
      result = db["interviews"].find_one({
          "_id": ObjectId(interview_id)
      })
      if user_id == str(result["interviewer_id"]):
          result = clients.get(result["interviewee_id"],0)
          print("=================")
          print("im interviewer")
          print(sid,"my socket id")
          #print(str(result["socket"]),"interviewee socket id")
          print("=================")
          if result !=  0:
              await sio.emit("PEER_JOINED",data={"sid":sid},to=result["socket"]) 
      else:
          result = clients.get(result["interviewer_id"],0)
          print("=================")
          print("im interviewee")
          print(sid,"my socket id")
          print(str(result["socket"]),"interviewer socket id")
          print("=================")
          if result !=  0:
            
              await sio.emit("PEER_JOINED",data={"sid":sid},to=result["socket"])      
  @sio.on("OFFER")
  async def offers(sid,data):
      new  = {
          "to":data["to"],
          "offer":data["offer"],
          "from":sid
      }
      print("OFFER",new["to"])
      await sio.emit("OFFER",data=new,to=new["to"])
  @sio.on("ANSWER")
  async def answers(sid,data):
      await sio.emit("ANSWER",data=data,to=data["to"])
  

  Terminal

   **OUTPUT FROM SERVER TERMINAL**
      =================
      im interviewer
      qBiuTDKXv8f_5s4oAAAD my socket id
      =================
      im interviewee
      TS3UnfTu8rJiIcdtAAAF my socket id
      qBiuTDKXv8f_5s4oAAAD interviewer socket id
      =================
      OFFER TS3UnfTu8rJiIcdtAAAF
  
• bazel build: failing to link external non-bazel shared library

  I am experimenting with Bazel for the first time. I am trying to build a shared library using Bazel-3.7.2. The shared library has an external non-Bazel library dependency. After Bazel build I get the new shared library ".so" file. But using ldd I cannot find the external dependency.

  The WORKSPACE file looks as follows. Here libxed.so is the extern shared library.

  # xed library
  new_local_repository(
      name = "libxed",
      path = "dependencies/xed/kits/xed-install-base",
      build_file_content = """
  cc_library(
      name = "libxed",
      srcs = ["lib/libxed.so"],
      hdrs = glob([
          "include/xed/*.h",
      ]),
      visibility = ["//visibility:public"],
  )
  """,
  )
  
  # xed header files
  new_local_repository(
      name = "libxed_headers",
      path = "dependencies/xed/kits/xed-install-base/include/xed",
      build_file_content = """
  cc_library(
      name = "xed",
      hdrs = glob([
          "*.h",
      ]),
      visibility = ["//visibility:public"],
  )
  """,
  )
  

  The BUILD file:

  load("@rules_cc//cc:defs.bzl", "cc_binary", "cc_library")
  
  cc_library(
      name = "themis",
      srcs = glob(
          ["src/main.cpp",
          "src/tools/Themis/*.cpp",
          ],
      ),
      hdrs = glob([
          "includes/tools/Themis/mytool.hpp",
      ]),
      strip_include_prefix = "includes",
      linkopts = ["-pthread", "-lrt", "-lunwind", "-ldl"],
      deps = [
         "@libxed_headers//:xed",
         "@libxed//:libxed",
      ],
      visibility = ["//visibility:public"],
  )
  

  After building the library it creates libthemis.so.

  ldd bazel-bin/libthemis.so
          linux-vdso.so.1 (0x00007ffe410ab000)
          libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f70e7de8000)
          libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f70e7a4a000)
          librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f70e7842000)
          libunwind.so.8 => /usr/lib/x86_64-linux-gnu/libunwind.so.8 (0x00007f70e7627000)
          libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f70e7423000)
          libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f70e7204000)
          libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f70e6e13000)
          /lib64/ld-linux-x86-64.so.2 (0x00007f70e8171000)
          libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f70e6bfb000)
          liblzma.so.5 => /lib/x86_64-linux-gnu/liblzma.so.5 (0x00007f70e69d5000)
  

  Here libthemis.so does not include libxed.so. Note that I can build the Themis library with Cmake correctly. How can I fix the Bazel build?
• undefined symbol: _ZTI13my_plugin_api during Boost::DLL tutorial

  I have problem running the very first example of Boost::DLL tutorial. At some point I just copied code from the git repo to be sure I didn't do any mistake. Didn't help. Both executable and shared lib compile and link properly. However, I still get the same error when running the program:

  terminate called after throwing an instance of 'boost::wrapexcept<boost::system::system_error>'
    what():  boost::dll::shared_library::load() failed (dlerror system message: ./libmy_plugin_sum.so: undefined symbol: _ZTI13my_plugin_api): Exec format error
  Interrupt (memory dump)
  

  The funny thing is I don't even have to try to import plugin to get this error... My question is what is happening and why?

  My abstract base (in file my_plugin_api.hpp):

  #include <boost/config.hpp>
  
  #include <string>
  
  class BOOST_SYMBOL_VISIBLE my_plugin_api {
  public:
      virtual std::string name() const = 0;
      virtual float calculate(float x, float y) = 0;
  
      virtual ~my_plugin_api();
  };
  

  My executable code (file main.cpp):

  #include <boost/dll/import.hpp> // for import_alias
  #include <iostream>
  #include "my_plugin_api.hpp"
  
  namespace dll = boost::dll;
  
  boost::dll::fs::path get_path(char* str) {
      return boost::dll::fs::path(str);
  }
  
  int main(int argc, char* argv[]) {
  
      boost::dll::fs::path lib_path = get_path(argv[1]);             // argv[1] contains path to directory with our plugin library
      boost::shared_ptr<my_plugin_api> plugin;            // variable to hold a pointer to plugin variable
      std::cout << "Loading the plugin" << std::endl;
      
      auto multiply = dll::import<double(double, double)>(   //importing single function from library
          lib_path/"my_plugin_sum",
          "multiply",
          dll::load_mode::append_decorations
      );
  
      std::cout << multiply(1.5,1.5) << "\n";
  }
  
  

  Now, the important part, the library code (file plugin.cpp):

  #include <iostream>
  
  #include <boost/config.hpp> // for BOOST_SYMBOL_EXPORT
  #include <boost/dll/alias.hpp>
  
  #include "my_plugin_api.hpp"
  
  namespace my_namespace {
  
  class my_plugin_sum : public my_plugin_api {
  public:
      my_plugin_sum() {
          std::cout << "Constructing my_plugin_sum" << std::endl;
      }
  
      std::string name() const {
          return "sum";
      }
  
      float calculate(float x, float y) {
          return x + y;
      }
     
      ~my_plugin_sum() {
          std::cout << "Destructing my_plugin_sum ;o)" << std::endl;
      }
  };
  
  extern "C" BOOST_SYMBOL_EXPORT my_plugin_sum plugin;
  my_plugin_sum plugin;
  
  } // namespace my_namespace
  
  extern "C" {
      BOOST_SYMBOL_EXPORT
      double multiply(double x, double y) { return x*y; }
  }
  

  Additional info:

  • System version: Ubuntu 20.10 (x64)
  • Compiler version: g++ (Ubuntu 10.2.0-13ubuntu1) 10.2.0
  • Boost version: 1.75.0
  • Executable compiled with: g++ main.cpp -o boost-plugin -ldl -lboost_filesystem
  • SO library compiled with: g++ -shared -fPIC -fvisibility="hidden" -o libmy_plugin_sum.so plugin.cpp

  It is enough to remove the following two lines of library code:

  extern "C" BOOST_SYMBOL_EXPORT my_plugin_sum plugin;
  my_plugin_sum plugin;
  

  and error disappears.

  Part of result of nm -C -D libmy_plugin_sum.so (run on version that generates error):

  0000000000011510 u guard variable for boost::system::detail::to_std_category(boost::system::error_category const&)::map_
  000000000000a9dc W my_plugin_api::my_plugin_api()
  000000000000a9dc W my_plugin_api::my_plugin_api()
                   U my_plugin_api::~my_plugin_api()
  000000000000a87c W boost::system::system_error::~system_error()
  .
  .
  .
  00000000000ad12 W std::operator==(std::_Rb_tree_iterator<std::pair<boost::system::error_category const* const, std::unique_ptr<boost::system::detail::std_category, std::default_delete<boost::system::detail::std_category> > > > const&, std::_Rb_tree_iterator<std::pair<boost::system::error_category const* const, std::unique_ptr<boost::system::detail::std_category, std::default_delete<boost::system::detail::std_category> > > > const&)
                   U std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*)
                   U typeinfo for my_plugin_api
  0000000000010ce0 V typeinfo for boost::system::system_error
  0000000000010d40 V typeinfo for boost::system::error_category
  

  List of objects of library version that doesn't cause any problems doesn't contain any my_plugin_api entry at all.

  EDIT:

  When looking at non-demangled symbols (nm -D libmy_plugin_sum.so) I get this:

  0000000000011510 u _ZGVZN5boost6system6detail15to_std_categoryERKNS0_14error_categoryEE4map_
  000000000000a9e2 W _ZN13my_plugin_apiC1Ev
  000000000000a9e2 W _ZN13my_plugin_apiC2Ev
                   U _ZN13my_plugin_apiD2Ev
  000000000000a882 W _ZN5boost6system12system_errorD0Ev
  
  ...
  
                   U _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc@@GLIBCXX_3.4
                   U _ZTI13my_plugin_api
  0000000000010ce0 V _ZTIN5boost6system12system_errorE
  
  ...
  
  000000000000d2a0 V _ZTSN5boost6system6detail22generic_error_categoryE
                   U _ZTV13my_plugin_api
                   U _ZTVN10__cxxabiv117__class_type_infoE@@CXXABI_1.3
  
• How to Import a registered Phaser3 GameObject from an external library; How to distribute Phaser3 GameObjects

  I think my question is "How do I distribute Phaser3 GameObjects in libraries which can be reused".

  Here is the issue:

  Below, in Base.js, is a Base custom GameObject, which I want to be reusable in lots of Phaser3 games.

  import Phaser from "phaser"
  
  export default class Base extends Phaser.GameObjects.Graphics {
    constructor(scene, x, y) {
      super(scene, x, y)
      this.fillStyle(0x770000).fillRect(x, y, 100, 100)
    }
  }
  
  Phaser.GameObjects.GameObjectFactory.register("base", function (x, y) {
    const base = new Base(this.scene, x, y)
    this.displayList.add(base)
    return base
  })
  

  This is how I consume the GameObject in a scene. Vanilla stuff.

  import Phaser from "phaser"
  import Base from "@localLibrary/base/lib/Base"   // <-- This fails to fire the `register` function. 
  # import Base from "./Base"  // <-- This works. 
  
  export default class PopitScene extends  Phaser.Scene  {
    create() {
      this.add.base(200, 200)
    }
  }
  

  When I try to import my GameObject file from a different repo, it fails to fire the register function, and the error message I get is: scene.add.base is not a function

  In this instance, I have installed the library npm i file:../base inside a folder called game1

  project
    |- base
    |- game1
    |- game2
  

  And the goal is to have different games reusing the same GameObjects inside the base library.
• Presence of risc-v float instructions for the (rv64ima-lp64) soft float compilaton

  I compiled glibc 2.33 for risc-v 64-bit(rv64ima-lp64) using the riscv-gnu-toolchain.

  The glibc was configured with following flags

  ./configure --host=riscv64-unknown-linux-gnu --prefix=${PREFIX} --disable-werror --enable-shared --enable-obsolete-rpc --with-headers=${KERNEL_HEADERS} --disable-multilib
  

  And the riscv-gnu-toolchain was configured and compiled with --with-arch=rv64ima and --with-abi=lp64

  But on doing objdump -D ld.so in elf directory of glibc build, I am getting floating point instructions i.e.

     83b2e:   317e                    fld ft2,504(sp)
     83b32:   0f00                    addi    s0,sp,912
     83b40:   0014f80f            0x14f80f
     83b4c:   0f10                    addi    a2,sp,912
     83b52:   7345                    lui t1,0xffff1
     83b5a:   0029990f            0x29990f
     83b62:   31d2                    fld ft3,304(sp)
     83b66:   0f20                    addi    s0,sp,920
     83b68:   00000d0f            0xd0f
     83b6c:   7645                    lui a2,0xffff1
     83b6e:   f209                    bnez    a2,83a70 <_end+0x60890>
     83b72:   2800                    fld fs0,16(s0)
     83b74:   0017a00f            0x17a00f
     83b80:   0f30                    addi    a2,sp,920
     83b86:   7945                    lui s2,0xffff1
     83b8c:   3800                    fld fs0,48(s0)
     83b8e:   0018b00f            0x18b00f
     83b96:   325f 0000 3140          0x31400000325f
     83ba0:   7b45                    lui s6,0xffff1
     83bae:   317e                    fld ft2,504(sp)
     83bc8:   04f20803            lb  a6,79(tp) # 4f <GLIBC_2.27+0x4f>
     83bd2:   a300                    fsd fs0,0(a4)
     83bf2:   000031c7            fmsub.s ft3,ft0,ft0,ft0,rup
     83bf6:   00015713            srli    a4,sp,0x0
     83bfa:   1300                    addi    s0,sp,416
     83bfc:   000004e7            jalr    s1,zero # 0 <GLIBC_2.27>
     83c0c:   a908                    fsd fa0,16(a0)
     83c10:   3b00                    fld fs0,48(a4)
     83c50:   3216                    fld ft4,352(sp)
     83c60:   31f80803            lb  a6,799(a6)
     83c6a:   3b00                    fld fs0,48(a4)
     83c80:   2208                    fld fa0,0(a2)
     83c8a:   325f 0000 6313          0x63130000325f
     83caa:   2b18                    fld fa4,16(a4)
  

  I am expecting some clarification on this, as the binary should not contain any float instructions.

  Thank you.
• crosscompilation from Linux to old macintosh 68000

  I would compiling a C program to old macintosh.

  How I can do this today? I would create normal gui program not linux distro on this device. Which compiler working, library for gui etc.

  My program is very simple. Hello world. gcc or llvm can do that?

  (similar original book, documents https://www.macintoshrepository.org/18756-mac-game-programming but using today tools)
• cannot compile raspberry kernel on NTFS disk

  Sorry for my bad english.

  I am trying to compile kernel source code of raspberry and jetson tx2 on a NTFS disk. compile kernel source code of jetson ok, no error. compile kernel source code of raspberry fail with bellow error message:

  *** Error during update of the configuration.
  
  make[3]: *** [/media/u2004/LINUX_SHARED/rasp/linux/scripts/kconfig/Makefile:39: silentoldconfig] Error 1
  make[2]: *** [/media/u2004/LINUX_SHARED/rasp/linux/Makefile:541: silentoldconfig] Error 2
  make[1]: *** No rule to make target 'include/config/auto.conf', needed by 'include/config/kernel.release'. Stop.
  make[1]: Leaving directory '/media/u2004/LINUX_SHARED/rasp/build_output'
  make: *** [Makefile:150: sub-make] Error 2
  

  no error when compile raspberry kernel source code in Ext4 disk.

  edit: add compile environment and script cross compile in Ubuntu 20.04 64bit. compile aarch32 with bellow script (compile ok in Ext4 partition).

  ROOT_DIR=/home/u2004/Desktop/dm
  KERNEL_BUILD_DIR=${ROOT_DIR}/linux/
  CROSS_COMPILE=${ROOT_DIR}/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/arm-linux-gnueabihf-
  BUILD_OUTPUT=${ROOT_DIR}/build_output
  INSTALL_MOD_PATH_EXT4=${ROOT_DIR}/copy_to_sdcard/ext4
  INSTALL_MOD_PATH_FAT32=${ROOT_DIR}/copy_to_sdcard/fat32
  ARCH=arm
  DEF_CONFIG=bcm2709_defconfig
  TARGET=kernel7
  
  git clone --depth=1 -b rpi-4.9.y https://github.com/raspberrypi/linux
  git clone https://github.com/raspberrypi/tools
  
  export CROSS_COMPILE=${CROSS_COMPILE}
  cd ${KERNEL_BUILD_DIR}
  make mrproper
  make ARCH=${ARCH} O=${BUILD_OUTPUT} ${DEF_CONFIG}
  make ARCH=${ARCH} O=${BUILD_OUTPUT} -j4 zImage modules dtbs
  make ARCH=${ARCH} INSTALL_MOD_PATH=${INSTALL_MOD_PATH_EXT4} modules_install
  

  please help. thank you
• undefined reference error in c++ during compiling

  I'm new with template in C++ and I'm puzzled on how I could run my program. The code I'm supposed to do is use a template to "create a static stack of any data type." This is the first time I'm working with templates and I only have a very basic knowledge about it. Hoping to get inputs!

  I'm using codio and the code is broken into three files: Main.cpp, Data.h, and Implementation.cpp. The error is this:

  /tmp/cckg9fEh.o: In function `main':
  Main.cpp:(.text+0x24): undefined reference to `IntStack<char>::IntStack(int)'
  Main.cpp:(.text+0x48): undefined reference to `IntStack<char>::push(char)'
  Main.cpp:(.text+0x6c): undefined reference to `IntStack<char>::push(char)'
  Main.cpp:(.text+0x90): undefined reference to `IntStack<char>::push(char)'
  Main.cpp:(.text+0xb4): undefined reference to `IntStack<char>::push(char)'
  Main.cpp:(.text+0xd8): undefined reference to `IntStack<char>::push(char)'
  Main.cpp:(.text+0xfe): undefined reference to `IntStack<char>::pop(char&)'
  Main.cpp:(.text+0x13b): undefined reference to `IntStack<char>::pop(char&)'
  Main.cpp:(.text+0x178): undefined reference to `IntStack<char>::pop(char&)'
  Main.cpp:(.text+0x1b5): undefined reference to `IntStack<char>::pop(char&)'
  Main.cpp:(.text+0x1f2): undefined reference to `IntStack<char>::pop(char&)'
  collect2: error: ld returned 1 exit status
  Stack_Project/test.sh: 6: Stack_Project/test.sh: ./Main.h: not found
  codio@smile-queen:~/workspace$ 
  

  My code is as follows:

  Data.h

  #ifndef INTSTACK_H
  #define INTSTACK_H
  #include <iostream>
  #pragma once
  
  template <class T>
  class IntStack
  {
    private:
      T *stackArray;
      int stackSize;
      int top;
  
    public:
      IntStack(int size);
      void push(T let);
      void pop(T &let);
      bool isFull();
      bool isEmpty();
  };
  
  #endif
  

  Implementation.cpp

  #include <iostream>
  #include "Data.h"
  using namespace std;
  
  template <class T>
  IntStack<T>::IntStack(int size)
  {
     stackArray = new T[size]; 
     stackSize = size; 
     top = -1;
  } 
  
  template <class T>
  void IntStack<T>::push(T let)
  {
     if (isFull())
     {
         cout << "The stack is full.\n";
     }
     else
     {
         top++;
         stackArray[top] = let;
     }
  }
  
  template <class T>
  void IntStack<T>::pop(T &let)
  {
     if (isEmpty())
     {
         cout << "The stack is empty.\n";
     }
     else
     {
         let = stackArray[top];
         top--;
     }
  }
  
  template <class T>
  bool IntStack<T>::isFull()
  {
     bool status;
  
     if (top == stackSize - 1)
         status = true;
     else
         status = false;
     return status;
  }
  
  template <class T>
  bool IntStack<T>::isEmpty()
  {
     bool status;
  
     if (top == -1)
         status = true;
     else 
         status = false;
     return status;
  }
  

  Main.cpp

  #include <iostream>
  #include "Data.h"
  using namespace std;
  
  int main()
  {
      IntStack<char> stack(5);
      char reclaim;
  
      cout << "Pushing M\n";
      stack.push('M');
      cout << "Pushing C\n";
      stack.push('C');
      cout << "Pushing P\n";
      stack.push('P');
      cout << "Pushing U\n";
      stack.push('U');  
      cout << "Pushing D \n";
      stack.push('D');
  
      cout << "Popping...\n";
      stack.pop(reclaim);
      cout << reclaim << endl;
      stack.pop(reclaim);
      cout << reclaim << endl;
      stack.pop(reclaim);
      cout << reclaim << endl;
      stack.pop(reclaim);
      cout << reclaim << endl;
      stack.pop(reclaim);
      cout << reclaim << endl;
  }
  

  Thanks for the help!
• undefined reference when including a header-file

  I try to code a Checkers game.

  To make it easier to read, I wanted to split it into several files, but I get an "undefined reference" error. So far, I have a main.cpp, a Board.cpp and a Board.hpp. It works, when its all in main.cpp, but once I split it up, and include the board header file, I get the error.

  I have done this before, and it looks just like how I've done it before, so I don't know why it's acting up now.

  main.cpp

  #include <iostream>
  #include <array>
  #include <cmath>
  #include "Board.hpp"
  
  class Gameplay
  {
     protected:
         std::array<std::array<char,8>,8> gameboard;   // Board with tokens on it
     public:
         //....
         //Beginning Set-Up
         void setup ();
         /...
  
         friend class Board;
  
  };
  
  //SetUp
  void Gameplay::setup ()
  {
      char user1 = '@';      //Symbol of User 1
      char user2 = 'c';
      Board plainBoard;     //board with no tokens    //These two lines is when I get the undefined
      plainBoard.create();                            //reference error
      gameboard = plainBoard.board;
      //...
  }
  

  Board.hpp

  #ifndef BOARD_HPP_INCLUDED
  #define BOARD_HPP_INCLUDED
  #endif // RECHNER_HPP_INCLUDED
  #include <iostream>
  #include <array>
  
  
  
  class Board
  {
  protected:
      std::array<std::array<char,8>,8> board;    //Plain Board
  public:
  //....
  friend class Gameplay;
  };
  

  board.cpp

  #include <iostream>
  #include <array>
  #include <cmath>
  #include "Board.hpp"
  
  //...
  

  The code works, I just get the #include part wrong. Errors: undefined reference to 'Board::create()' undefined reference to 'Board::~Board()'
• Undefined reference to signalr::value::as_string()

  It is about compiling the sample project of the SignalR-Client-Cpp Here.

  The Libs was generated using 32 bits in SUSE Linux Enterprise Server 12 (x86_64) with GCC 7.5.0.

  The error occuered by linking

  g++ -g -m32 -z muldefs -lz -L/home/ihil/SignalR-Client-Cpp/build.release/bin/ -lsignalrclient -o "SignalrBetaClient" HubConnectionSample.o;
  HubConnectionSample.o: In Funktion »std::_Function_handler<void (signalr::value const&), chat()::{lambda(signalr::value const&)#1}>::_M_invoke(std::_Any_data const&, signalr::value const&)«:
  HubConnectionSample.cpp:(.text+0x284): Warnung: undefinierter Verweis auf »signalr::value::as_string() const«
  HubConnectionSample.o: In Funktion »std::_Function_handler<void (signalr::value const&, std::__exception_ptr::exception_ptr), send_message(signalr::hub_connection&, std::string const&)::{lambda(signalr::value const&, std::__exception_ptr::exception_ptr)#1}>::_M_invoke(std::_Any_data const&, signalr::value const&, std::__exception_ptr::exception_ptr)«:
  HubConnectionSample.cpp:(.text+0x41c): Warnung: undefinierter Verweis auf »signalr::value::as_string() const«
  HubConnectionSample.o: In Funktion »send_message(signalr::hub_connection&, std::string const&)«:
  HubConnectionSample.cpp:(.text+0x5b9): Warnung: undefinierter Verweis auf »signalr::value::value(std::string&&)«
  HubConnectionSample.cpp:(.text+0x5d4): Warnung: undefinierter Verweis auf »signalr::value::value(std::string const&)«
  HubConnectionSample.cpp:(.text+0x6d3): Warnung: undefinierter Verweis auf »signalr::hub_connection::invoke(std::string const&, signalr::value const&, std::function<void (signalr::value const&, std::__exception_ptr::exception_ptr)>)«
  HubConnectionSample.o: In Funktion »chat()«:
  HubConnectionSample.cpp:(.text+0xcad): Warnung: undefinierter Verweis auf »signalr::hub_connection_builder::create(std::string const&)«
  HubConnectionSample.cpp:(.text+0xd94): Warnung: undefinierter Verweis auf »signalr::hub_connection::on(std::string const&, std::function<void (signalr::value const&)> const&)«
  collect2: Fehler: ld gab 1 als Ende-Status zurück
  

  Although the list of symbles of the library shows that the undifined references are found

  nm -a bin/libsignalrclient.so | grep 'hub_connection_builder'
  00000000 a hub_connection_builder.cpp
  00030b70 T _ZN7signalr22hub_connection_builder12with_loggingESt10shared_ptrINS_10log_writerEENS_11trace_levelE
  00030d60 T _ZN7signalr22hub_connection_builder16with_http_clientESt10shared_ptrINS_11http_clientEE
  00030ca0 T _ZN7signalr22hub_connection_builder22with_websocket_factoryESt8functionIFSt10shared_ptrINS_16websocket_clientEERKNS_21signalr_client_configEEE
  00030e80 T _ZN7signalr22hub_connection_builder5buildEv
  00030530 T _ZN7signalr22hub_connection_builder6createERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE
  00030700 T _ZN7signalr22hub_connection_builderaSEOS0_
  00030890 T _ZN7signalr22hub_connection_builderaSERKS0_
  00030660 T _ZN7signalr22hub_connection_builderC1EOS0_
  00030460 T _ZN7signalr22hub_connection_builderC1ERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE
  00030560 T _ZN7signalr22hub_connection_builderC1ERKS0_
  00030660 T _ZN7signalr22hub_connection_builderC2EOS0_
  00030460 T _ZN7signalr22hub_connection_builderC2ERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE
  00030560 T _ZN7signalr22hub_connection_builderC2ERKS0_
  000309c0 T _ZN7signalr22hub_connection_builderD1Ev
  000309c0 T _ZN7signalr22hub_connection_builderD2Ev