-Wconversion warning

[miporto]

I'm receiving a -Wconversion warning when including and compiling the latest release of the library. I read #239 but the errors showed are different (although it's the same flag that sends the warning), also the links present there are down.
Here is the complete output:

In file included from .../foo.cpp:3:0:
.../json.hpp: In instantiation of ‘nlohmann::basic_json<ObjectType, ArrayType, StringType, 
BooleanType, NumberIntegerType, NumberFloatType, AllocatorType>::escape_string(const 
string_t&) [with ObjectType = std::map; ArrayType = std::vector; StringType = 
std::basic_string<char>; BooleanType = bool; NumberInteger
Type = long int; NumberFloatType = double; AllocatorType = std::allocator; 
nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, 
NumberFloatType, AllocatorType>::string_t = std::basic_string<char>]::__lambda3’:
.../json.hpp:5455:40:   required from ‘struct nlohmann::basic_json<ObjectType, ArrayType, 
StringType, BooleanType, NumberIntegerType, NumberFloatType, 
AllocatorType>::escape_string(const string_t&) [with ObjectType = std::map; ArrayType = 
std::vector; StringType = std::basic_string<char>; BooleanType = bool; NumberIntegerType = long 
int; NumberFloatType = double; AllocatorType = std::allocator; nlohmann::basic_json<ObjectType, 
ArrayType, StringType, BooleanType, NumberIntegerType, NumberFloatType, 
AllocatorType>::string_t = std::basic_string<char>]::__lambda3’
.../json.hpp:5458:25:   required from ‘static nlohmann::basic_json<ObjectType, ArrayType, 
StringType, BooleanType, NumberIntegerType, NumberFloatType, AllocatorType>::string_t 
nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, 
NumberFloatType, AllocatorType>::escape_string(const string_t&) [with ObjectType = std::map; 
ArrayType = std::vector; StringType = std::basic_string<char>; BooleanType = bool; 
NumberIntegerType = long int; NumberFloatType = double; AllocatorType = std::allocator; 
nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, 
NumberFloatType, AllocatorType>::string_t = std::basic_string<char>]’
.../json.hpp:5536:48:   required from ‘void nlohmann::basic_json<ObjectType, ArrayType, 
StringType, BooleanType, NumberIntegerType, NumberFloatType, 
AllocatorType>::dump(std::ostream&, bool, unsigned int, unsigned int) const [with ObjectType = 
std::map; ArrayType = std::vector; StringType = std::basic_string<char>; BooleanType = bool; 
NumberIntegerType = long int; NumberFloatType = double; AllocatorType = std::allocator; 
std::ostream = std::basic_ostream<char>]’
.../json.hpp:1892:61:   required from ‘nlohmann::basic_json<ObjectType, ArrayType, StringType, 
BooleanType, NumberIntegerType, NumberFloatType, AllocatorType>::string_t 
nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, 
NumberFloatType, AllocatorType>::dump(int) const [with ObjectType = std::map; ArrayType = 
std::vector; StringType = std::basic_string<char>; BooleanType = bool; NumberIntegerType = long 
int; NumberFloatType = double; AllocatorType =
 std::allocator; nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, 
NumberIntegerType, NumberFloatType, AllocatorType>::string_t = std::basic_string<char>]’
.../json.hpp:8209:25:   required from here
.../json.hpp:5457:72: error: conversion to ‘char’ from ‘int’ may alter its value [-Werror=conversion]
                             return (v < 10) ? ('0' + v) : ('a' + v - 10);
                                                                        ^
.../json.hpp:5457:72: error: conversion to ‘char’ from ‘int’ may alter its value [-Werror=conversion]
.../json.hpp: In instantiation of ‘static nlohmann::basic_json<ObjectType, ArrayType, StringType, 
BooleanType, NumberIntegerType, NumberFloatType, AllocatorType>::string_t 
nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, 
NumberFloatType, AllocatorType>::escape_string(const
 string_t&) [with ObjectType = std::map; ArrayType = std::vector; StringType = 
std::basic_string<char>; BooleanType = bool; NumberIntegerType = long int; NumberFloatType = 
double; AllocatorType = std::allocator; nlohmann::basic_json<ObjectType, ArrayType, StringType, 
BooleanType, NumberIntegerType, NumberFloatType, AllocatorType>::string_t = std::basic
_string<char>]’:
.../json.hpp:5536:48:   required from ‘void nlohmann::basic_json<ObjectType, ArrayType, 
StringType, BooleanType, NumberIntegerType, NumberFloatType, 
AllocatorType>::dump(std::ostream&, bool, unsigned int, unsigned int) const [with ObjectType = 
std::map; ArrayType = std::vector; StringType = std::basic_string<char>; BooleanType = bool; 
NumberIntegerType = long int; NumberFloatType = double; AllocatorType = std::allocator; 
std::ostream = std::basic_ostream<char>]’
.../json.hpp:1892:61:   required from ‘nlohmann::basic_json<ObjectType, ArrayType, StringType, 
BooleanType, NumberIntegerType, NumberFloatType, AllocatorType>::string_t 
nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, 
NumberFloatType, AllocatorType>::dump(int) const [with ObjectType = std::map; ArrayType = 
std::vector; StringType = std::basic_string<char>; BooleanType = bool; NumberIntegerType = long 
int; NumberFloatType = double; AllocatorType =
 std::allocator; nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, 
NumberIntegerType, NumberFloatType, AllocatorType>::string_t = std::basic_string<char>]’
.../json.hpp:8209:25:   required from here
.../json.hpp:5462:51: error: conversion to ‘char’ from ‘int’ may alter its value [-Werror=conversion]
                     { 'u', '0', '0', hexify(c >> 4), hexify(c & 0x0f)
                                                   ^
cc1plus: all warnings being treated as errors

• gcc (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4
• Compile flags: -std=c++11 -Wall -Werror -Wconversion -Wno-unused-parameter -Wextra -Wtype-limits -pedantic -pedantic-errors

[nlohmann]

Could you please try the latest version in the develop branch? I remember fixing some conversion warnings there.

[miporto]

I tried with the develop version, but now I receive an error that didn't appear with the release library.

In file included from .../foo.cpp:6:0:
.../json.hpp: In instantiation of 
‘nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, 
NumberUnsignedType, NumberFloatType, AllocatorType>::value_type& 
nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, 
NumberUnsignedType, NumberFloatType, AllocatorType>::operator[]
(nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, 
NumberUnsignedType, NumberFloatType, AllocatorType>::size_type) [with ObjectType = std::map; 
ArrayType = std::vector; StringType = std::basic_string<char>; BooleanType = bool; 
NumberIntegerType = long int; NumberUnsignedType = long unsigned int; NumberFloatType = 
double; AllocatorType = std::allocator; nlohmann::basic_json<ObjectType, ArrayType, StringType, 
BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, 
AllocatorType>::reference = nlohmann::basic_json<>&; nlohmann::basic_json<ObjectType, 
ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, 
NumberFloatType, AllocatorType>::value_type = nlohmann::basic_json<>; 
nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, 
NumberUnsignedType, NumberFloatType, AllocatorType>::size_type = long unsigned int]’:
.../foo.cpp:21:49:   required from here
.../json.hpp:1062:5: error: conversion from 
‘nlohmann::basic_json<>::value_t’ to non-scalar type ‘nlohmann::basic_json<>::type_data_t’ 
requested
     basic_json() = default;
     ^
.../json.hpp:3307:17: note: synthesized method ‘nlohmann::basic_json<ObjectType, ArrayType, 
StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, 
AllocatorType>::basic_json() [with ObjectType = std::map; ArrayType = std::vector; StringType = 
std::basic_string<char>; BooleanType = bool; NumberIntegerType = long int; NumberUnsignedType 
= long unsigned int; NumberFloatType = double; AllocatorType = std::allocator]’ first required here 
                 m_value.array->push_back(basic_json());
                 ^

[nlohmann]

This is a known error of GCC 4.8 which is therefore not supported by the library, see https://github.com/nlohmann/json#supported-compilers. Can you try with a more recent compiler?

[nlohmann]

I had another look at your first output. These warnings have been fixed with #239 (see commit db5c9ec). (The links are down, because the feature branch has been merged and deleted since.)

[miporto]

Ok, thanks for your help!

[guygman]

Hi, I'm running into the same issue, but with commit 15a314a.
I'm using Clang 3.4.2 for Linux

[nlohmann]

This is very strange. Can you please provide the concrete warning output?

[guygman]

here's the build output.
the error is at the point of instantiation of a class with an nlohmann::json member.

[ 91%] Building CXX object common/CMakeFiles/common.dir/config.cpp.o
In file included from /home/centos/shared/src_master_origin/common/config.h:8:0,
from /home/centos/shared/src_master_origin/common/config.cpp:1:
/home/centos/shared/src_master_origin/common/../3rdparty/json/src/json.hpp: In instantiation of 'nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType> nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType>::parser::parse() [with ObjectType = std::map; ArrayType = std::vector; StringType = std::basic_string; BooleanType = bool; NumberIntegerType = long int; NumberUnsignedType = long unsigned int; NumberFloatType = double; AllocatorType = std::allocator]':
/home/centos/shared/src_master_origin/common/../3rdparty/json/src/json.hpp:5722:36: required from 'static nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType> nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType>::parse(const string_t&, nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType>::parser_callback_t) [with ObjectType = std::map; ArrayType = std::vector; StringType = std::basic_string; BooleanType = bool; NumberIntegerType = long int; NumberUnsignedType = long unsigned int; NumberFloatType = double; AllocatorType = std::allocator; nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType>::string_t = std::basic_string; nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType>::parser_callback_t = std::function<bool(int, nlohmann::basic_json<>::parse_event_t, nlohmann::basic_json<>&)>]'
/home/centos/shared/src_master_origin/common/../3rdparty/json/src/json.hpp:8920:98: required from here
/home/centos/shared/src_master_origin/common/../3rdparty/json/src/json.hpp:1060:5: error: conversion from 'nlohmann::basic_json<>::value_t' to non-scalar type 'nlohmann::basic_json<>::type_data_t' requested
basic_json() = default;
^
/home/centos/shared/src_master_origin/common/../3rdparty/json/src/json.hpp:8611:42: note: synthesized method 'nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType>::basic_json() [with ObjectType = std::map; ArrayType = std::vector; StringType = std::basic_string; BooleanType = bool; NumberIntegerType = long int; NumberUnsignedType = long unsigned int; NumberFloatType = double; AllocatorType = std::allocator]' first required here
return result.is_discarded() ? basic_json() : result;
^
make[2]: *** [common/CMakeFiles/common.dir/config.cpp.o] Error 1

[nlohmann]

Hi @guygman, thanks for providing more information. It seems as if Clang is choking on an implicit conversion from type_data_t to basic_json. In fact, I am planning to remove type_data_t altogether - could you please try to compile your example with this branch?

[guygman]

Hi,

compiling with that branch worked much better! there was no conversion error.

[nlohmann]

That branch has now been merge with develop, see f86fe57 .