Definition of ssize_t in FmqDefines.h clashes with definition in osconfig.h of DCMTK

[helmut-steiner]

osconfig.h in DCMTK (a widely used DICOM Toolkit) already defines ssize_t as long:

/* Define `ssize_t' to `long' if <sys/types.h> does not define. */
#define HAVE_NO_TYPEDEF_SSIZE_T
#ifdef HAVE_NO_TYPEDEF_SSIZE_T
#define ssize_t long
#endif

When used in combination with finalmq the following error occurs in FmqDefines.h (Visual Studio 2022, SDK 19041):

[helmut-steiner]

Is it possible to use long instead of int64_t?
Then the simple solution would be to include the following wrapper around the using line:

#if !defined(ssize_t)
using ssize_t = std::int64_t;
#endif

Edit:
In MSVC long is 4 bytes even on 64-bit operating systems. So only 32bit. To be equal it would need to be long long.
See https://learn.microsoft.com/en-us/cpp/cpp/fundamental-types-cpp?view=msvc-170 for MSVC
and https://en.cppreference.com/w/cpp/types/integer for standard C++
So the question is, does it need to be 64bit or is 32bit sufficient?

[beckdave]

Actually, ssize_t depends on the platform.
For 64 bit platform ssize_t has 64 size. For 32 bit platform, it has 32 bit.
There should be even an ifdef for the different platforms.
_WIN64 can be used for the ifdef

[helmut-steiner]

Yes, unfortunately different libraries define ssize_t differently. This makes compiling and linking them in one project really hard.
OpenSSL does define their own ossl_ssize_t in e_os2.h e.g.:

# ifndef ossl_ssize_t
#  define ossl_ssize_t ssize_t
#  if defined(SSIZE_MAX)
#   define OSSL_SSIZE_MAX SSIZE_MAX
#  elif defined(_POSIX_SSIZE_MAX)
#   define OSSL_SSIZE_MAX _POSIX_SSIZE_MAX
#  else
#   define OSSL_SSIZE_MAX ((ssize_t)(SIZE_MAX>>1))
#  endif
# endif

As DCMTK is included first it sets the stage in our project. So ssize_t is long. finalmq library by itself compiles with int64_t. If I try to link both libraries and got some code of finalmq included the code is built with long but in finalmq it has a different type thus linking the built code with the library throws many linking errors.
I had to change the FmqDefines.h to

#if defined(WIN32) || defined(__MINGW32__)
#include <winsock2.h>
#if !defined(ssize_t)
using ssize_t = long;
#endif
#define strtof32 strtof
#define strtof64 strtod
#define MSG_MORE MSG_PARTIAL
#else
#include <sys/types.h>
using SOCKET = int;
namespace finalmq
{
static const SOCKET INVALID_SOCKET = -1;
} // namespace finalmq
#endif

and recompile everything. Afterwards compiling and linking both libraries work. Maybe a solution like in OpenSSL with another define works to keep things separated. What do you think?

[beckdave]

Do you compile for 32 bit platform or 64?

[helmut-steiner]

Both

[beckdave]

This is the definition for size_t in the windows header vcruntime.h

// Definitions of common types
#ifdef _WIN64
typedef unsigned __int64 size_t;
typedef __int64 ptrdiff_t;
typedef __int64 intptr_t;
#else
typedef unsigned int size_t;
typedef int ptrdiff_t;
typedef int intptr_t;
#endif

So, size_t is different on the platforms. This should also be for ssize_t.

I would define ssize_t in finalmq as:

#if !defined(ssize_t)
#if defined(_WIN64)
using ssize_t = std::int64_t;
#else
using ssize_t = std::int32_t;
#endif
#endif

---

I think, DCMTK should also fix it the same way.

But in case, they will not fix it, we could do the following solution:

#if !defined(ssize_t)
#if defined(_WIN64) && !defined(FINALMQ_WIN64_SSIZE_AS_32BIT)
using ssize_t = std::int64_t;
#else
using ssize_t = std::int32_t;
#endif
#endif

I would also define FINALMQ_WIN64_SSIZE_AS_32BIT as an cmake option. This will solve your problem.

[helmut-steiner]

Perfect. I will have a look into the DCMTK repository if this has been already changed in the dev branch and contact the authors if it hasn't.

[helmut-steiner]

I got the response of the DCMTK team. They added it to their issue tracker:
https://support.dcmtk.org/redmine/issues/1131

They have a valid point: The above fix is only for WIN64. Other 64bit systems that might have not defined SSIZE_T will still use the wrong type.