[Python] fix C linkage warning

[asfimport]

When using pyarrow interface from a c++ library one will get the following compiler warning:

warning: 'unwrap_table' has C-linkage specified, but returns user-defined type 'arrow::Status' which is incompatible with C [-Wreturn-type-c-linkage]
ARROW_EXPORT Status unwrap_table(PyObject* table, std::shared_ptr<Table>* out);
This is due to a Cython artifact.

 

Reporter: Viktor Gal / @vigsterkr
Assignee: Antoine Pitrou / @pitrou

PRs and other links:

• GitHub Pull Request #5425

_{Note: This issue was originally created as ARROW-2317. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
What happens if you add a extern "C++" block surrounding the declarations in pyarrow.h?

Like this:

diff --git a/cpp/src/arrow/python/pyarrow.h b/cpp/src/arrow/python/pyarrow.h
index e637627..2980541 100644
--- a/cpp/src/arrow/python/pyarrow.h
+++ b/cpp/src/arrow/python/pyarrow.h
@@ -24,6 +24,8 @@
 
 #include "arrow/util/visibility.h"
 
+extern "C++" {
+
 namespace arrow {
 
 class Array;
@@ -80,5 +82,6 @@ ARROW_EXPORT PyObject* wrap_record_batch(const std::shared_ptr<RecordBatch>& bat
 
 }  // namespace py
 }  // namespace arrow
+}  // extern "C++"
 
 #endif  // ARROW_PYTHON_PYARROW_H

[asfimport]

Viktor Gal / @vigsterkr:
perfect! this not only solved the compiler problem but as well the problem i was facing with the mentioned "Symbol not found" in the thread of "unwrap_table in c++ library" on the dev mailing list

[asfimport]

Antoine Pitrou / @pitrou:
Did you report the issue to the Cython project as well? Their bug tracker is at https://github.com/cython/cython/

[asfimport]

Antoine Pitrou / @pitrou:
Also, can you explain how exactly you are using pyarrow from your C++ library? Just #include "pyarrow.h"? Something else? Are you using Cython at all?

[asfimport]

Wes McKinney / @wesm:
This seems like an easy patch, @vigsterkr can you submit a PR?

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 5425
#5425