Fixed compilation error

[xiaosq2000]

Fixed "include/record3d/Record3DStructs.h:33:21: error: field ‘udid’ has incomplete type 'std::string'"

[lllangWV]

Just to add some context for this pr:

I was able to reproduce this build failure on a clean system:

• OS: Ubuntu 24.04 LTS (x86_64)
• Compiler: GCC 13.3.0
• CMake: 3.28.3
• Python: 3.11.0

The error looks like this:

include/record3d/Record3DStructs.h:33:21: error: field ‘udid’ has incomplete type ‘std::string’
   33 |         std::string udid{ "" };
      |                     ^~~~
/usr/include/c++/13/bits/stringfwd.h:72:11: note: declaration of ‘std::string’
   72 |     class basic_string;
      |           ^~~~~~~~~~~~

This happens because Record3DStructs.h uses std::string but doesn’t explicitly include <string>.

On older GCC/libstdc++ versions (e.g. GCC 9/10), this compiled fine because <string> was indirectly included by other headers.
However, starting with GCC 13, libstdc++ intentionally reduced accidental header inclusions. From the [Porting to GCC 13 guide:

Some C++ Standard Library headers have been changed to no longer include other headers that were being used internally by the library. As such, C++ programs that used standard library components without including the right headers will no longer compile.

The following headers are used less widely in libstdc++ and may need to be included explicitly when compiling with GCC 13:

• <string> (for std::string, std::to_string, std::stoi, etc.)
• <system_error> (for std::error_code, std::system_error, etc.)
• <cstdint>, <cstdio>, <cstdlib>

So this PR is the correct fix: explicitly including <string> makes the header self‑contained and portable across compilers.

I tested the patch locally and can confirm it resolves the build error on GCC 13.

[AnnabellaMacaluso]

Hi, I was wondering why this was removed from recent updates to main?