Possibility to use without the dependency to file io and streams to use in intel sgx enclaves

[theShmoo]

includes some macros to be defined for using without file io.

[coveralls]

Coverage remained the same at 99.982% when pulling 572343b on theShmoo:without-io into 18a5f4c on nlohmann:develop.

[nlohmann]

Please run make amalgamate to make sure the single header is properly generated. The CI currently fails because this.

[nlohmann]

Sorry for the inactivity. I have one question left: you write in #2728 that the headers for I/O do not exist. But in your change you seem not to exclude any headers if JSON_NO_IO is defined.

[theShmoo]

Ah that is true!
The headers exist in Intels SGX implementation of the standard library. But they are empty:

for example in iostream: https://github.com/intel/linux-sgx/blob/master/sdk/tlibcxx/include/iostream

Should I remove the includes so that it also usable for other applications?

[nlohmann]

Yes, please. The use case may be still quite special, but at lease it would not assume include included headers are empty. I could imagine that that flag may be usable for some if they want to reduce compile times if they do not use I/O in their project.

[theShmoo]

Does the build pipeline fail because of me or is this an error in the pipeline?

[nlohmann]

This seems to be an issue in the pipeline. I need to investigate.

[nlohmann]

Please update the branch - I just merged #2817 to fix the CI.

[nlohmann]

Looks good to me.

[theShmoo]

Thank you very much for your support and your review!

[nlohmann]

Thanks!