C++ compilation error with g++15 caused by including <cstdint> but using int64_t instead of std::int64_t

[DominiquePelle-TomTom]

Zserio version and language
Zserio: 2.16.0
Language: C++

Describe the bug

Generated C++ code includes <cstdint> but uses types like uint64_t, int64_t (etc.) without the std:: namespace prefix. This is incorrect and not portable. It causes compilation errors when building with gcc15 such as:

/home/dope/.conan/data/zserio/2.16.0/_/_/build/2a1643475ff774383687d1e8922f3bc3015406f5/src/compiler/extensions/cpp/runtime/src/zserio/JsonEncoder.h: In static member function ‘static void zserio::JsonEncoder::encodeIntegral(std::ostream&, T)’:
/home/dope/.conan/data/zserio/2.16.0/_/_/build/2a1643475ff774383687d1e8922f3bc3015406f5/src/compiler/extensions/cpp/runtime/src/zserio/JsonEncoder.h:67:76: error: ‘uint64_t’ was not declared in this scope [-Wtemplate-body]
   67 |     using U = typename std::conditional<std::is_signed<T>::value, int64_t, uint64_t>::type;
      |                                                                            ^~~~~~~~

To fix it, either:

• use #include <cstdint> and std::uint64_t in zserio code (preferred and more modern solution, but you have to replace many int64_t into std::int64_t, same for other types like int8_t, etc.)
• or use #include <stdint.h> and int64_t in zserio code. This is the less preferred and is the old pre-c++11 way. Since it does not use namespace, it is more prone to name collisions.

How to reproduce
N/A

Expected behavior
Generated C++ code should compile on any compiler

[mikir]

Thanks for the report. Currently, we directly support only g++7 and g++11. We should investigate this to understand clearly the differencies between gcc versions.

I will put this issue to the current milestone. However, we are working on C++17 generator now, so it will take some time. If this issue is urgent, please write us a note here. Thanks.

[DominiquePelle-TomTom]

g++7 and g++11.

Well, the issue is clear enough even if you do not use gcc-15 anyway:

• if you include (which is the case in zserio source code), then you have to use std::int64_t (not int64_t)
• if you include <stdint.h>, then you have to use int64_t (not std::int64_t)

Same for other types obviously (std::int8_t, std::uint8_t, etc.)

So it's quite trivial to fix, i.e. replace types such as int64_t with std::int64_t.

If this issue is urgent, please write us a note here

The issue is not urgent for me. Our current toolchain builds successfully, but I noticed the issue when trying to build with gcc-15 (which is not officially used yet in my company).