如何为 jsoncpp 编写 cmake 模块？

我想用jsoncpp用于编写 C++ 代码来解析 JSON 文件。让我解释一下我做了什么。我创建了一个CMakeLists.txt我做了一个FindJsoncpp.cmake以及一个简单的 c++ 文件来测试jsoncpp。当我在不使用 cmake 的情况下编译 C++ 源代码时-I/usr/include/jsoncpp/ -ljsoncpp效果很好。但是当我尝试使用 cmake 构建它时它找不到json.h我包含在我的 C++ 源代码中的头文件。

这是我的CMakeLists.txt:

cmake_minimum_required (VERSION 2.6)
project (Parser)

set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_SOURCE_DIR}/cmake/Modules/")

include(LibFindMacros)

message("----------- trying to find Jsoncpp-------------")
find_package(Jsoncpp)

if(Jsoncpp_FOUND)
    message("INFO: we found LibJsoncpp on your pc.")
    message(Jsoncpp_FOUND = ${Jsoncpp_FOUND})
    message(Jsoncpp_INCLUDE_DIR = ${Jsoncpp_INCLUDE_DIR}) 
    message(Jsoncpp_LIBRARY = ${Jsoncpp_LIBRARY})
else(Jsoncpp_FOUND)
    message("WARNING: we couldn't find LibJsoncpp on your pc. DLC is disabled.")
endif(Jsoncpp_FOUND)

#set(LIBS ${Jsoncpp_LIBRARY})

# Set the include dir variables and the libraries and let libfind_process do the rest.
# NOTE: Singular variables for this library, plural for libraries this this lib depends on.
set(Jsoncpp_PROCESS_INCLUDES Jsoncpp_INCLUDE_DIR)
set(Jsoncpp_PROCESS_LIBS Jsoncpp_LIBRARY)

# add the executable
add_executable(jsonparser jsonparser.cpp)

这就是FindJsoncpp.cmake我写的：

# - Try to find Jsoncpp
# Once done, this will define
#
#  Jsoncpp_FOUND - system has Jsoncpp
#  Jsoncpp_INCLUDE_DIRS - the Jsoncpp include directories
#  Jsoncpp_LIBRARIES - link these to use Jsoncpp

include(LibFindMacros)

# Use pkg-config to get hints about paths
libfind_pkg_check_modules(Jsoncpp_PKGCONF jsoncpp)

# Include dir
find_path(Jsoncpp_INCLUDE_DIR
  NAMES json/json.h
#  PATHS ./jsoncpp/
  PATHS ${Jsoncpp_PKGCONF_INCLUDE_DIRS} # /usr/include/jsoncpp/json
)

# Finally the library itself
find_library(Jsoncpp_LIBRARY
  NAMES jsoncpp
  PATHS ${Jsoncpp_PKGCONF_LIBRARY_DIRS}
#  PATH ./jsoncpp/
)

set(Jsoncpp_PROCESS_INCLUDES Jsoncpp_INCLUDE_DIR)
set(Jsoncpp_PROCESS_LIBS Jsoncpp_LIBRARY)
libfind_process(Jsoncpp)

最后是一个简单的 C++ 代码，名为jsonparser.cpp测试它：

#include <iostream>
#include <fstream>
#include <json/json.h>
using namespace std;

void printSongInfo(Json::Value song){
    std::clog<<"\n-----------printing a song-------------\n";
    std::clog<<"Name="<<song["name"];
    std::clog<<"Artist="<<song["artist"];
}

int main(){

    std::ifstream catalogFile("catalog.json");

    Json::Value root;   // will contains the root value after parsing.
    Json::Reader reader;
    bool parsingSuccessful = reader.parse( catalogFile, root );
    if ( !parsingSuccessful ){
        // report to the user the failure and their locations in the document.
        std::cout  << "Failed to parse configuration\n"
                   << reader.getFormattedErrorMessages();
        return 1;
    }

    //parsing songs
    const Json::Value songs = root["songs"];
    for ( int index = 0; index < songs.size(); ++index ){  // Iterates over the sequence elements.
       printSongInfo(songs[index] );
    }
    return 0;
}

当我运行jsonparser.cpp使用下面的命令它工作得很好。

g++ -I/usr/include/jsoncpp/ -ljsoncpp jsonparser.cpp

但是当我尝试使用它时cmake我收到此错误：

$~/jsoncppTest/build$ cmake ..
-- The C compiler identification is GNU 4.7.3
-- The CXX compiler identification is GNU 4.7.3
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
----------- trying to find Jsoncpp-------------
-- Found PkgConfig: /usr/bin/pkg-config (found version "0.26") 
-- checking for module 'jsoncpp'
--   found jsoncpp, version 0.6.0
-- Found Jsoncpp 
INFO: we found LibJsoncpp on your pc.
Jsoncpp_FOUND=TRUE
Jsoncpp_INCLUDE_DIR=/usr/include/jsoncpp
Jsoncpp_LIBRARY=/usr/lib/libjsoncpp.so
-- Configuring done
-- Generating done
-- Build files have been written to: ~/jsoncppTest/build
$~/jsoncppTest/build$ make
Scanning dependencies of target jsonparser
[100%] Building CXX object CMakeFiles/jsonparser.dir/jsonparser.cpp.o
~/jsoncppTest/jsonparser.cpp:3:23: fatal error: json/json.h: No such file or directory
compilation terminated.
make[2]: *** [CMakeFiles/jsonparser.dir/jsonparser.cpp.o] Error 1
make[1]: *** [CMakeFiles/jsonparser.dir/all] Error 2
make: *** [all] Error 2

它找不到json/json.h头文件，但之前已经在cmake中创建了jsoncpp库。我检查了jsoncpp.pc文件并发现 ti OK。我不知道我做错了什么！任何帮助，将不胜感激。

我正在使用具有多体系结构支持的 ubuntu 13.04。我听说 64 位编译器存在 jsoncpp 问题，但不知道是否是这样。

好的，我有一个可以在我的系统上编译良好的解决方案。查找 jsoncpp 很棘手，因为 json-c 安装了一个具有相同名称的标头，并且在我的系统上，该标头位于 /usr/include/json/json.h 下。要使其正常工作，您必须进行以下更改：

在 FindJsoncpp.cmake 中:

# Include dir
find_path(Jsoncpp_INCLUDE_DIR
  NAMES json/features.h
  PATH_SUFFIXES jsoncpp
  PATHS ${Jsoncpp_PKGCONF_INCLUDE_DIRS} # /usr/include/jsoncpp/json
)

搜索 json/features.h 而不是 json/json.h 可以避免在我的系统上找到 json-c 的 json.h 文件，该文件不兼容。

在 CMakeLists.txt 中 :

include_directories(${Jsoncpp_INCLUDE_DIR})
add_executable(jsonparser jsonparser.cpp)
target_link_libraries(jsonparser ${Jsoncpp_LIBRARY})

这里设置了找到的目录，因此 CMake 实际上使用它们。

在 jsonparser.cpp 中:

const Json::Value songs = root["songs"];
for ( int index = 0; index < songs.size(); ++index ){  // Iterates over the sequence elements.
   std::clog<<"Name="<<songs[index]["name"];
   std::clog<<"Artist="<<songs[index]["artist"];
}

您的原始代码无法编译，因此我用上面的代码替换了有问题的部分。您是否忘记声明歌曲变量？

我还删除了 getFormattedErrorMessages() 调用，因为我只有 jsoncpp 0.5.0，其中该函数不可用。但这应该没有什么区别。

让我知道这是否适合您。