Fixes Cppcheck warnings

[Xav83]

Hi @nlohmann and other mainteners,

First of all, I must say that I love your work on this librairy.
It feels really easy to use, and to read code using this library ! ❤️

I have created this issue to talk about the warnings that cppcheck found on this project.
I'm currently experimenting with both this library and cppcheck on some little side projects. And doing so, I've ended up with cppcheck warnings me about some elements inside the json library.

So the purpose of this issue is to talk about the warnings from cppcheck, to address them when they are relevant, so that other people which are going to have both this library and cppcheck] in their project, as little as warnings as possible.

Here is the list of the warnings I've got for now:

(1)[include\nlohmann\json.hpp:5076]: (style) Variable 'm_value.object->emplace' is reassigned a value before the old one has been used.
(2)[include\nlohmann\detail\conversions\to_chars.hpp:585]: (style) The expression 'kAlpha >= -60' is always true.
(3)[include\nlohmann\detail\conversions\to_chars.hpp:586]: (style) The expression 'kGamma <= -32' is always true.
(4)[include\nlohmann\detail\output\serializer.hpp:726]: (style) The expression 'thousands_sep != '\0'' is always false because 'thousands_sep' and ''\0'' represent the same value.
(5)[include\nlohmann\detail\output\serializer.hpp:736]: (style) The expression 'decimal_point != '\0'' is always false because 'decimal_point' and ''\0'' represent the same value.
(6)[include\nlohmann\detail\input\binary_reader.hpp:650]: (style) Unsigned expression 'mant' can't be negative so it is unnecessary to test it.
(7)[include\nlohmann\json.hpp:837]: (style) Local variable object shadows outer function
(8)[include\nlohmann\detail\input\input_adapters.hpp:339]: (style) Class 'input_adapter' has a constructor with 1 argument that is not explicit.
(9)[include\nlohmann\detail\input\input_adapters.hpp:342]: (style) Class 'input_adapter' has a constructor with 1 argument that is not explicit.
(10)[include\nlohmann\detail\input\input_adapters.hpp:346]: (style) Class 'input_adapter' has a constructor with 1 argument that is not explicit.
(11)[include\nlohmann\detail\input\input_adapters.hpp:349]: (style) Class 'input_adapter' has a constructor with 1 argument that is not explicit.
(12)[include\nlohmann\detail\input\input_adapters.hpp:352]: (style) Class 'input_adapter' has a constructor with 1 argument that is not explicit.
(13)[include\nlohmann\detail\input\input_adapters.hpp:355]: (style) Class 'input_adapter' has a constructor with 1 argument that is not explicit.
(14)[include\nlohmann\detail\input\input_adapters.hpp:377]: (style) Class 'input_adapter' has a constructor with 1 argument that is not explicit.
(15)[include\nlohmann\detail\input\input_adapters.hpp:421]: (style) Class 'input_adapter' has a constructor with 1 argument that is not explicit.
(16)[include\nlohmann\detail\input\input_adapters.hpp:429]: (style) Class 'input_adapter' has a constructor with 1 argument that is not explicit.
(17)[include\nlohmann\detail\json_ref.hpp:18]: (style) Class 'json_ref' has a constructor with 1 argument that is not explicit.
(18)[include\nlohmann\detail\json_ref.hpp:22]: (style) Class 'json_ref' has a constructor with 1 argument that is not explicit.
(19)[include\nlohmann\detail\json_ref.hpp:26]: (style) Class 'json_ref' has a constructor with 1 argument that is not explicit.
(20)[include\nlohmann\detail\json_ref.hpp:33]: (style) Class 'json_ref' has a constructor with 1 argument that is not explicit.
(21)[include\nlohmann\detail\output\output_adapters.hpp:105]: (style) Class 'output_adapter' has a constructor with 1 argument that is not explicit.
(22)[include\nlohmann\detail\output\output_adapters.hpp:108]: (style) Class 'output_adapter' has a constructor with 1 argument that is not explicit.
(23)[include\nlohmann\detail\output\output_adapters.hpp:111]: (style) Class 'output_adapter' has a constructor with 1 argument that is not explicit.
(24)[include\nlohmann\json.hpp:1162]: (style) Class 'basic_json' has a constructor with 1 argument that is not explicit.
(25)[include\nlohmann\json.hpp:1186]: (style) Class 'basic_json' has a constructor with 1 argument that is not explicit.
(26)[include\nlohmann\json.hpp:1253]: (style) Class 'basic_json' has a constructor with 1 argument that is not explicit.
(27)[include\nlohmann\json.hpp:1290]: (style) Class 'basic_json' has a constructor with 1 argument that is not explicit.
(28)[include\nlohmann\json.hpp:1730]: (style) Class 'basic_json' has a constructor with 1 argument that is not explicit.
(29)[include\nlohmann\detail\output\binary_writer.hpp:869]: (style) Consider using std::accumulate algorithm instead of a raw loop.

Some of them may be false positive, but others can be relevant, so this is why I've made this issue. The good news, is that all the warnings I have got are flagged as "style", not as error or warning, so their are less likely to bother most of people using cppcheck. 😄

If we successly correct all the warnings (and silence the false positive), we may even imagine adding cppcheck to the CI of the library. 🤞

Let me know what you think about this idea. If you agree with the purpose of this issue, I'll gladly help to reach it.

For technical information, I've used the version 1.87 of cppcheck on the version 3.7.0 of the json library, on Windows, with Visual Studio 2017. You can find the repository on which I'm currently running this here

In a few minutes, I will also add a Pull Request which handles the warnings 6 and 29. 🔜

[Xav83]

PS: I don't know is this issue should be flagged as a feature request or as anything else, so I made it a regular issue.

[t-b]

@Xav83 Closed by #1760?

[Xav83]

@t-b I don't think this issue should be closed, for now.
The Pull Request #1760 only fixed the warning 6 and 29.
The others remains unfixed yet

[nlohmann]

If I remove the warnings on non-explicit constructors (which are not a bug, but a feature for this library), we are left with the following issues:

(1)[include\nlohmann\json.hpp:5076]: (style) Variable 'm_value.object->emplace' is reassigned a value before the old one has been used.
(2)[include\nlohmann\detail\conversions\to_chars.hpp:585]: (style) The expression 'kAlpha >= -60' is always true.
(3)[include\nlohmann\detail\conversions\to_chars.hpp:586]: (style) The expression 'kGamma <= -32' is always true.
(4)[include\nlohmann\detail\output\serializer.hpp:726]: (style) The expression 'thousands_sep != '\0'' is always false because 'thousands_sep' and ''\0'' represent the same value.
(5)[include\nlohmann\detail\output\serializer.hpp:736]: (style) The expression 'decimal_point != '\0'' is always false because 'decimal_point' and ''\0'' represent the same value.
(7)[include\nlohmann\json.hpp:837]: (style) Local variable object shadows outer function

PRs welcome!

[t-b]

And even nicer than a PR fixes these issues would be adding the cppcheck to CI so that the codebase stays clean as well.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[Xav83]

Those 2 warnings:

(4)[include\nlohmann\detail\output\serializer.hpp:726]: (style) The expression 'thousands_sep != '\0'' is always false because 'thousands_sep' and ''\0'' represent the same value.
(5)[include\nlohmann\detail\output\serializer.hpp:736]: (style) The expression 'decimal_point != '\0'' is always false because 'decimal_point' and ''\0'' represent the same value.

seems to be false positive, since the expression can be true since their are initialize as such:

, loc(std::localeconv())
, thousands_sep(loc->thousands_sep == nullptr ? '\0' : * (loc->thousands_sep))
, decimal_point(loc->decimal_point == nullptr ? '\0' : * (loc->decimal_point))

but cppcheck must deduce the warnings because of the default which is const too:

/// the locale's thousand separator character
const char thousands_sep = '\0';
/// the locale's decimal point character
const char decimal_point = '\0';