如何在简单的 C++ 项目中使用 Poco 库？

Question

这是我项目的目录结构：

poco/
CMakeLists.txt
main.cpp

注意：poco 目录包含使用此命令从 Poco 的 github 存储库下载的所有文件：

git clone --recurse-submodules https://github.com/pocoproject/poco.git

这是CMakeLists.txt的内容：

cmake_minimum_required(VERSION 3.4.1)
add_executable(
    main
    main.cpp
)
add_subdirectory(poco)
include_directories(
   poco/ApacheConnector/include
   poco/CppParser/include
   poco/CppUnit/include
   poco/Crypto/include
   poco/Data/include
   poco/Encodings/include
   poco/Foundation/include
   poco/JSON/include
   poco/MongoDB/include
   poco/Net/include
   poco/NetSSL_OpenSSL/include
   poco/NetSSL_Win/include
   poco/openssl/build/include
   poco/PDF/include
   poco/Redis/include
   poco/SevenZip/include
   poco/Util/include
   poco/XML/include
   poco/Zip/include
)

target_link_libraries(main ${POCO_LIBRARIES})

这是main.cpp的内容：

#include <iostream>
#include <Poco/Net/HTTPClientSession.h>
using namespace std;
int main() {
    std::cout << "here";

    return 0;
}

在我运行这些命令后（在其结构出现的目录中）：

$mkdir _build && cd _build
$cmake ..
$make

我遇到了这些错误：

[  0%] Building CXX object CMakeFiles/main.dir/main.cpp.o
[  1%] Linking CXX executable main
CMakeFiles/main.dir/main.cpp.o: In function `Poco::Net::Impl::IPv6SocketAddressImpl::host() const':
/home/gandalf/Desktop/pocoTest/poco/Net/include/Poco/Net/SocketAddressImpl.h:143: undefined reference to `Poco::Net::IPAddress::IPAddress(void const*, unsigned int, unsigned int)'
CMakeFiles/main.dir/main.cpp.o: In function `Poco::Net::Impl::IPv6SocketAddressImpl::~IPv6SocketAddressImpl()':
/home/gandalf/Desktop/pocoTest/poco/Net/include/Poco/Net/SocketAddressImpl.h:118: undefined reference to `Poco::Net::Impl::SocketAddressImpl::~SocketAddressImpl()'
CMakeFiles/main.dir/main.cpp.o: In function `Poco::Net::Impl::IPv6SocketAddressImpl::~IPv6SocketAddressImpl()':
/home/gandalf/Desktop/pocoTest/poco/Net/include/Poco/Net/SocketAddressImpl.h:118: undefined reference to `Poco::Net::Impl::SocketAddressImpl::~SocketAddressImpl()'
CMakeFiles/main.dir/main.cpp.o: In function `Poco::Net::Impl::IPv4SocketAddressImpl::~IPv4SocketAddressImpl()':
/home/gandalf/Desktop/pocoTest/poco/Net/include/Poco/Net/SocketAddressImpl.h:56: undefined reference to `Poco::Net::Impl::SocketAddressImpl::~SocketAddressImpl()'
CMakeFiles/main.dir/main.cpp.o: In function `Poco::Net::Impl::IPv4SocketAddressImpl::~IPv4SocketAddressImpl()':
/home/gandalf/Desktop/pocoTest/poco/Net/include/Poco/Net/SocketAddressImpl.h:56: undefined reference to `Poco::Net::Impl::SocketAddressImpl::~SocketAddressImpl()'
CMakeFiles/main.dir/main.cpp.o: In function `Poco::Net::Impl::IPv4SocketAddressImpl::host() const':
/home/gandalf/Desktop/pocoTest/poco/Net/include/Poco/Net/SocketAddressImpl.h:81: undefined reference to `Poco::Net::IPAddress::IPAddress(void const*, unsigned int)'
CMakeFiles/main.dir/main.cpp.o:(.data.rel.ro._ZTIN4Poco3Net4Impl21IPv4SocketAddressImplE[_ZTIN4Poco3Net4Impl21IPv4SocketAddressImplE]+0x10): undefined reference to `typeinfo for Poco::Net::Impl::SocketAddressImpl'
CMakeFiles/main.dir/main.cpp.o:(.data.rel.ro._ZTIN4Poco3Net4Impl21IPv6SocketAddressImplE[_ZTIN4Poco3Net4Impl21IPv6SocketAddressImplE]+0x10): undefined reference to `typeinfo for Poco::Net::Impl::SocketAddressImpl'
CMakeFiles/main.dir/main.cpp.o:(.data.rel.ro._ZTVN4Poco3Net4Impl21IPv4SocketAddressImplE[_ZTVN4Poco3Net4Impl21IPv4SocketAddressImplE]+0x50): undefined reference to `Poco::Net::Impl::IPv4SocketAddressImpl::toString[abi:cxx11]() const'
CMakeFiles/main.dir/main.cpp.o:(.data.rel.ro._ZTVN4Poco3Net4Impl21IPv6SocketAddressImplE[_ZTVN4Poco3Net4Impl21IPv6SocketAddressImplE]+0x50): undefined reference to `Poco::Net::Impl::IPv6SocketAddressImpl::toString[abi:cxx11]() const'
collect2: error: ld returned 1 exit status
CMakeFiles/main.dir/build.make:94: recipe for target 'main' failed
make[2]: *** [main] Error 1
CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/main.dir/all' failed
make[1]: *** [CMakeFiles/main.dir/all] Error 2
Makefile:151: recipe for target 'all' failed
make: *** [all] Error 2

据我所知，Poco::Net::IPAddress::IPAddress 必须是Poco::Net::IPAddress。而且我不知道为什么链接器会在Poco::Net::IPAddress 中添加额外的IPAddress。 而这个问题似乎是由 CMakeLists.txt 中的错误引起的 那么我该如何解决呢？

Answer 1

target_link_libraries(main ${POCO_LIBRARIES}) 行无法按预期工作。该变量仅在查找模块中定义。它甚至可能不适用于现代软件包。

如果你想使用 poco 作为项目子目录，那么我建议链接到他们的目标：

cmake_minimum_required(VERSION 3.4.1)

add_executable(
    main
    main.cpp
)

add_subdirectory(poco)
target_link_libraries(main PUBLIC PocoNet ...) # replace `...` by all poco library you use

Answer 2

我也有类似的问题。我确实构建了以下测试用例。它基于 Linux 系统（opensuse）。这个例子并不完美——不能保证。

bash 命令：

$ git clone --depth=1 --branch=master --recurse-submodules https://github.com/pocoproject/poco.git
$ cd poco && mkdir poco-build && cd poco-build
$ cmake -H .. -B . -DCMAKE_INSTALL_PREFIX=~/libs
$ cmake --build . --target install

bash 例程将编译 poco 库并在 ~/libs 本地安装所需的 headers/libraries/cmake/... 文件。这当然可以改变。

---

使用以下文件。

CMakeLists.txt

cmake_minimum_required(VERSION 3.21)

project(PocoTimer)
set(CMAKE_PREFIX_PATH /home/<user>/libs/poco/lib/cmake/Poco)

find_package(Poco REQUIRED Foundation)

add_executable(
    main main.cpp
)

target_link_libraries(
    main
    PRIVATE Poco::Foundation
)

main.cpp

#include "Poco/Timer.h"
#include "Poco/Thread.h"
#include "Poco/Stopwatch.h"
#include <iostream>

/*
 * Main application 
 */

class PocoTimer
{
public:
    //------------
    PocoTimer() { stopWatch.start(); }
    //------------
    void PrintElapsedTime(Poco::Timer& timer)
    {
      std::cout << "Time elapsed: " << stopWatch.elapsed() / 1000 << " milliseconds." << std::endl;
    }
private:
    Poco::Stopwatch stopWatch;
};


int main() {

PocoTimer pocoTimer;
Poco::Timer timer(250, 500);
// -- print command -- //
timer.start(Poco::TimerCallback<PocoTimer>(pocoTimer, &PocoTimer::PrintElapsedTime));
Poco::Thread::sleep(5000);
timer.stop();

}

---

您可以在CMakeLists.txt 中使用cmake 标志而不是set(CMAKE_PREFIX_PATH ...)。如果您想使用不同的 Poco 实例，这将使其更加灵活。

例如，如果您将 Poco“安装”到 ~/libs：

$ cmake -H. -B./build \
      -DPoco_DIR='/home/<user>/libs/poco/lib/cmake/Poco'

或

$ cmake -H. -B./build \
      -DCMAKE_PREFIX_PATH='/home/<user>/libs/poco/lib/cmake/Poco'

或

$ cmake -H. -B./build \
      -DCMAKE_MODULE_PATH='/home/<user>/libs/poco/lib/cmake/Poco'