I'm having the following C code:

static void* (*ppmalloc)(size_t) = malloc;
static void (*ppfree)(void*) = free;

I want to covert this code in D so I try to do the following:

static void* function(size_t)*ppmalloc = malloc;
static void  function(void*)*ppfree = free;

If I do that, I'm getting the following error message:

Error: function `core.stdc.stdlib.malloc(ulong size)` is not callable using argument types `()`

I'm also trying to do the same using "pureMalloc" and "pureFree" instead but this time I'm getting the following error:

cannot implicitly convert expression `pureMalloc()(size_t size)` of type `void` to `extern (C) void* function(ulong)*`

Any ideas?

On Sunday, 10 October 2021 at 10:44:15 UTC, rempas wrote:

static void* (*ppmalloc)(size_t) = malloc;
static void (*ppfree)(void*) = free;

static void* function(size_t)*ppmalloc = malloc;
static void  function(void*)*ppfree = free;

Error: function `core.stdc.stdlib.malloc(ulong size)` is not callable using argument types `()`

cannot implicitly convert expression `pureMalloc()(size_t size)` of type `void` to `extern (C) void* function(ulong)*`

Hello rempas.

This is the way:

import core.stdc.stdlib : malloc, free;
extern(C) void* function(ulong) mallocPointer = &malloc;
extern(C) void function(void*) freePointer = &free;

function in the type is already a function pointer. Not immediately obvious though: You also must annotate the type with extern(C) otherwise it will not work.

On Sunday, 10 October 2021 at 11:26:18 UTC, Elmar wrote:

import core.stdc.stdlib : malloc, free;
extern(C) void* function(ulong) mallocPointer = &malloc;
extern(C) void function(void*) freePointer = &free;

Thanks, I'm converting a library from C to D so I have to fix all the other bugs first to see If it's working but probably it will. Have an amazing day my friend!

On Sunday, 10 October 2021 at 13:10:27 UTC, rempas wrote:

Hopefully it will :-) .

D has some good C support. You can call any C function from D by declaring it extern(C) <function-signature>.

The language subset "BetterC" is required for calling D functions from C though. Unfortunately, the runtime features of BetterC are limited and some of C's language features aren't availabe like C99 variable-length-arrays. "BetterC" is like programming in C with little more comfort but phobos is unusable which makes BetterC almost no improvement over C. BetterC helper librarys like Tanya or Tango do exist.

In that case it can indeed be better for you to convert the program's entry point into D code. This is unfortunate because it prevents C code bases from using D.

There is a tool C++ Conversion Wizard which could be able to convert C++ and C to D but I don't know how good it is and whether it's usable for free on a GNU/Linux derivative OS. It's only half-automatic.

On Sunday, 10 October 2021 at 13:52:57 UTC, Elmar wrote:

Actually I know about BetterC and how to call C functions from D and visa versa. I would also disagree that "BetterC" is almost no improvement over C as about 90% of the language is there!! C++ classes are also supported

On Sunday, 10 October 2021 at 13:52:57 UTC, Elmar wrote:

Oh well, I could also be wrong with BetterC support of Tanya and Tango but both are alterantives to Phobos.

On Sunday, 10 October 2021 at 13:56:06 UTC, rempas wrote:

Nice :-) , you're right. I need to be more optimistic here. Happy coding.

On Sunday, 10 October 2021 at 13:52:57 UTC, Elmar wrote:

This is false.

You can use any D features when calling it from C, you just need to provide an init and term function that is called from C that runtime initialize and terminate for the full experience.

I don't know tanya, but Tango has absolutely nothing to do with betterC. It is a set of classes that use the full runtime.

On Sunday, 10 October 2021 at 14:00:37 UTC, Elmar wrote:

Thanks a lot! Happy coding to you too!

On 10/10/21 6:44 AM, rempas wrote:

static void* (*ppmalloc)(size_t) = malloc;
static void (*ppfree)(void*) = free;

static void* function(size_t)*ppmalloc = malloc;
static void  function(void*)*ppfree = free;

Error: function `core.stdc.stdlib.malloc(ulong size)` is not callable using argument types `()`

cannot implicitly convert expression `pureMalloc()(size_t size)` of type `void` to `extern (C) void* function(ulong)*`

I know most of this is answered already, but I would suggest actually just:

auto ppmalloc = &malloc;

which all of D's type inference to allow you to declare the appropriate function type.

BTW, you get the error because in D, empty parentheses are optional. So when you say malloc, it really means malloc(). Which is one big reason why the & operator is required.

-Steve