Json: How can I use it from gcc on RPI

[kuzmanzs]

Hi,

I would like to create hello world json example with gcc on Raspberry.
I have runned 'make' but I do not see install option.
How can I install/use it on RPI?

[xsacha]

You can use it with CMake
$ mkdir build && cd build
$ cmake .. -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/place/to/install/it
$ make -j 4 install

[nlohmann]

@xsacha The library itself contains of a single header in single_include. You do not need to install it - it is sufficient to copy the json.hpp file wherever you put your include files.

[xsacha]

@nlohmann Can't say I've ever done that (copy the file).

[kuzmanzs]

I have started @xsacha variant but I had to terminate, it takes too long.
Later I will start it again. At the end it should be installed to ie. /usr/local/include as json.a or?

I have downloaded the single_include json.hpp
I tried so:
hello.cpp

#include <iostream>
#include <json>
int main()
{
  cout << "Hello World!" << endl;
  return 0;
}

hpp file is saved to same dir:
hello.cpp json.hpp

tried to run following command:
g++ hello.cpp -o hello -I.

I got
hello.cpp:2:16: fatal error: json: No such file or directory #include <json> ^ compilation terminated.

[nlohmann]

If the json.hpp header is in the same directory, you can use

#include "json.hpp"

The result of the installation will not be a static or dynamic library, but just a C++ header. As the library uses templates, you cannot precompile it.

[kuzmanzs]

yes I can use "" thanks.
I have changed it.
But now I got lot of errors:
g++ hello.cpp -o hello
In file included from /usr/include/c++/4.9/initializer_list:36:0, from json.hpp:42, from hello.cpp:2: /usr/include/c++/4.9/bits/c++0x_warning.h:32:2: error: #error This file requires compiler and library support for the ISO C++ 2011 standard. This support is currently experimental, and must be enabled with the -std=c++11 or -std=gnu++11 compiler options. #error This file requires compiler and library support for the \ ^ In file included from hello.cpp:2:0: json.hpp:92:36: warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11 std::size_t chars_read_total = 0; ^ json.hpp:94:43: warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11 std::size_t chars_read_current_line = 0; ^ json.hpp:96:30: warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11 std::size_t lines_read = 0; ^ json.hpp:99:5: error: âconstexprâ does not name a type constexpr operator size_t() const ..

With the make I should get the same json.hpp under -DCMAKE_INSTALL_PREFIX=/place/to/install/it as yours?

[kuzmanzs]

I am testing with g++ hello.cpp -o hello -std=c++11

[nlohmann]

Yes, you need to use -std=c++11.

[kuzmanzs]

It works :) thanks for the nice lib!

just one thing:
When I run the make I should get the same json.hpp under -DCMAKE_INSTALL_PREFIX=/place/to/install/it as yours?

[xsacha]

If you're using the single header you don't need CMake or to install it.

[nlohmann]

When you call make install, all it does is compile the unit tests (which you can switch off by -DBUILD_TESTING=Off) and create the following structure in the directory you pass via -DCMAKE_INSTALL_PREFIX:

├── include
│   └── nlohmann
│       └── json.hpp
└── lib
    └── cmake
        └── nlohmann_json
            ├── nlohmann_jsonConfig.cmake
            ├── nlohmann_jsonConfigVersion.cmake
            └── nlohmann_jsonTargets.cmake

You do not need the files in lib, unless you do more with CMake. File include/nlohmann/json.hpp is the same as single_include/nlohmann/json.hpp from the repository.

[nlohmann]

@kuzmanzs Do you need further assistance in this issue?

[kuzmanzs]

@nlohmann : everything is working fine, thanks.