如何为jsoncpp编写cmake模块？

Question

我想jsoncpp用来编写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和FindJsoncpp.cmake一个简单的c ++文件进行测试jsoncpp.当我在没有使用cmake的情况下编译C++源代码时,-I/usr/include/jsoncpp/ -ljsoncpp它运行正常.但是当我尝试使用cmake构建它时,它找不到json.h我在c ++源代码中包含的头文件.

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)

最后一个简单的C++代码调用jsonparser.cpp它来测试它:

#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.cppwith with命令时它工作得很好.

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

但是当我尝试使用它时,cmake我得到了这个错误:

$~/jsoncppTest/build$ 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,但它之前在cmake中创建了jsoncpp库.我检查了jsoncpp.pc文件,发现确定.我不知道我做错了什么!任何帮助,将不胜感激.

我正在使用ubuntu 13.04和multiarch支持.我听说过有关64位编译器的jsoncpp问题,但不知道是不是这样.

Answer 1

好的,我有一个可以在我的系统上编译好的解决方案.查找jsoncpp很棘手,因为json-c安装了一个具有相同名称的头,并且在我的系统上,该头位于/usr/include/json/json.h下.要使其工作,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,这是不兼容的.

在CMakeLists.txt中:

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

这里找到了找到的目录,因此CMake实际上使用了它们.

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"];
}

你的原始代码没有编译,所以我用上面的代码替换了有问题的代码.你忘了宣布歌曲变量吗？

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.但这不应该有所作为.

如果这对您有用,请告诉我.