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SWIG Wrapper Generation

Using swig to generate wrapper it's easy thanks to the modern UseSWIG module (CMake >= 3.14).

note: SWIG automatically put its target(s) in all, thus cmake --build build will also call swig and generate _module.so.

Policy

UseSWIG is impacted by two policies:

  • CMP0078:UseSWIG generates standard target names (CMake 3.13+).
  • CMP0086: UseSWIG honors SWIG_MODULE_NAME via -module flag (CMake 3.14+).

That's why I recommnend to use CMake >= 3.14 with both policies set to new for SWIG development.

int64_t Management

When working on a k8 (aka x86_64) architecture, you may face issue with int64_t and uint64_t management.

First long long and long int are different types and int64_t is just a typedef on one of them...

Linux

On Linux we have:

sizeof(long long): 8
sizeof(long int): 8
sizeof(int64_t): 8

Gcc

First try to find where and how the compiler define int64_t and uint64_t.

grepc -rn "typedef.*int64_t;" /lib/gcc
/lib/gcc/x86_64-linux-gnu/9/include/stdint-gcc.h:43:typedef __INT64_TYPE__ int64_t;
/lib/gcc/x86_64-linux-gnu/9/include/stdint-gcc.h:55:typedef __UINT64_TYPE__ uint64_t;

So we need to find this compiler macro definition

gcc -dM -E -x c /dev/null | grep __INT64                 
#define __INT64_C(c) c ## L
#define __INT64_MAX__ 0x7fffffffffffffffL
#define __INT64_TYPE__ long int

gcc -dM -E -x c++ /dev/null | grep __INT64
#define __INT64_C(c) c ## L
#define __INT64_MAX__ 0x7fffffffffffffffL
#define __INT64_TYPE__ long int

Clang

clang -dM -E -x c++ /dev/null | grep INT64_TYPE
#define __INT64_TYPE__ long int
#define __UINT64_TYPE__ long unsigned int

Clang, GNU compilers:
-dM dumps a list of macros.
-E prints results to stdout instead of a file.
-x c and -x c++ select the programming language when using a file without a filename extension, such as /dev/null

Ref: https://web.archive.org/web/20190803041507/http://nadeausoftware.com/articles/2011/12/c_c_tip_how_list_compiler_predefined_macros

MacOS

On Catalina 10.15 we have:

sizeof(long long): 8
sizeof(long int): 8
sizeof(int64_t): 8

Clang

clang -dM -E -x c++ /dev/null | grep INT64_TYPE
#define __INT64_TYPE__ long long int
#define __UINT64_TYPE__ long long unsigned int

with: -dM dumps a list of macros.
-E prints results to stdout instead of a file.
-x c and -x c++ select the programming language when using a file without a filename extension, such as /dev/null

Ref: https://web.archive.org/web/20190803041507/http://nadeausoftware.com/articles/2011/12/c_c_tip_how_list_compiler_predefined_macros

Windows

Contrary to macOS and Linux, Windows 64bits (x86_64) try hard to keep compatibility, so we have:

sizeof(long int): 4
sizeof(long long): 8
sizeof(int64_t): 8

Visual Studio 2019

Thus, in stdint.h we have:

#if _VCRT_COMPILER_PREPROCESSOR

typedef signed char        int8_t;
typedef short              int16_t;
typedef int                int32_t;
typedef long long          int64_t;
typedef unsigned char      uint8_t;
typedef unsigned short     uint16_t;
typedef unsigned int       uint32_t;
typedef unsigned long long uint64_t;

SWIG int64_t management stuff

First, take a look at Swig stdint.i. So, when targeting Linux you must use define SWIGWORDSIZE64 (i.e. -DSWIGWORDSIZE64) while on macOS and Windows you must not define it.

Now the bad news, even if you can control the SWIG typedef using SWIGWORDSIZE64, SWIG Java and SWIG CSHARP do not take it into account for typemaps...

So you may want to use this for Java:

#if defined(SWIGJAVA)
#if defined(SWIGWORDSIZE64)
%define PRIMITIVE_TYPEMAP(NEW_TYPE, TYPE)
%clear NEW_TYPE;
%clear NEW_TYPE *;
%clear NEW_TYPE &;
%clear const NEW_TYPE &;
%apply TYPE { NEW_TYPE };
%apply TYPE * { NEW_TYPE * };
%apply TYPE & { NEW_TYPE & };
%apply const TYPE & { const NEW_TYPE & };
%enddef // PRIMITIVE_TYPEMAP
PRIMITIVE_TYPEMAP(long int, long long);
PRIMITIVE_TYPEMAP(unsigned long int, long long);
#undef PRIMITIVE_TYPEMAP
#endif // defined(SWIGWORDSIZE64)
#endif // defined(SWIGJAVA)

and this for .Net:

#if defined(SWIGCSHARP)
#if defined(SWIGWORDSIZE64)
%define PRIMITIVE_TYPEMAP(NEW_TYPE, TYPE)
%clear NEW_TYPE;
%clear NEW_TYPE *;
%clear NEW_TYPE &;
%clear const NEW_TYPE &;
%apply TYPE { NEW_TYPE };
%apply TYPE * { NEW_TYPE * };
%apply TYPE & { NEW_TYPE & };
%apply const TYPE & { const NEW_TYPE & };
%enddef // PRIMITIVE_TYPEMAP
PRIMITIVE_TYPEMAP(long int, long long);
PRIMITIVE_TYPEMAP(unsigned long int, unsigned long long);
#undef PRIMITIVE_TYPEMAP
#endif // defined(SWIGWORDSIZE64)
#endif // defined(SWIGCSHARP)

So int64_t (i.e. long int in this case) will be correctly bind to Java/.Net primitive type long.

swig_add_library()

You can use OUTPUT_DIR to change the output directory for the .py file e.g.:

swig_add_library(pyFoo
  TYPE SHARED
  LANGUAGE python
  OUTPUT_DIR ${CMAKE_BINARY_DIR}/python/${PROJECT_NAME}/Foo
  SOURCES foo.i)

Doxygen

Since swig 4.0, swig can now extract doxygen comments from C++ to inject it in Python and Java.

Csharp documentation

note: Doxygen to csharp was planned but currently is not supported.