[gdal-dev] Updating requirements to C++20 for GDAL 3.13 ?

[Even Rouault]

Hi,

any thoughts on :

1) updating our requirements to build GDAL to C++20 ?

2) and making use of it in our exported C++ headers ? (thus requiring 
C++ consumers of our API to also be C++20)

Our current situation is C++17 required to build GDAL, and our C++ 
exported headers are C++11 compatible (except some newer ones like 
gdalalgorithm_cpp.h, and some bits in )

We already have 2 (optional) dependencies requiring C++20: Poppler and 
PDFium.  The next version of libarrow/libparquet will also require 
C++20. Note that C++20 is currenly only enabled in GDAL in the drivers 
whose dependencies require it.

C++20 should not be an issue with the recent gcc/clang/MSVC. It would 
exclude the old-old-Ubuntu LTS 20.04 whose gcc 9 has only very partial 
support for it, but 20.04 standard support ended a few months ago, so 
not really relevant to consider for new GDAL version.  I'm not totally 
sure about Ubuntu 22.04. It has partial support with its default gcc 11, 
and improved one with gcc 12 that is also available. At the time GDAL 
3.13 will be released, Ubuntu 26.04 will be released, so 24.04 will be 
old-LTS, and 22.04 old-old-LTS so discarding it if it becomes too much 
of an inconvenience seems fine to me.

A few things that might be interesting in C++20 for our purposes:

- bit manipulation offered by <bit>
- std::span , particularly when bridging C and C++ API and passing 
non-constant size arrays around
- defaulted C++20 == operator
- std::string/string_view::starts_with/ends_with  (finally !)
- container.contains() (finally !)

Even

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