Calling V from C section too small

[nicolasventer]

Hello,
I want to call V from C. But since the documentation is really short, I don't know how I can do it.
This is what I've tried:
In a.v:

module a

[export: 'my_custom_c_name']
fn foo() {
	println("foo")
}

In b.c:

#include "a.v"

int main()
{
	my_custom_c_name();
}

And in cmd, I execute gcc b.c and I got:

> gcc b.c
In file included from b.c:1:
a.v:1:1: error: unknown type name 'module'
    1 | module a
      | ^~~~~~
a.v:3:2: error: 'export' undeclared here (not in a function)       
    3 | [export: 'my_custom_c_name']
      |  ^~~~~~
a.v:3:8: error: expected ']' before ':' token
    3 | [export: 'my_custom_c_name']
      |        ^
      |        ]
a.v:3:10: warning: character constant too long for its type        
    3 | [export: 'my_custom_c_name']
      |          ^~~~~~~~~~~~~~~~~~
b.c: In function 'main':
b.c:5:9: warning: implicit declaration of function 'my_custom_c_name' [-Wimplicit-function-declaration]
    5 |         my_custom_c_name();
      |         ^~~~~~~~~~~~~~~~

Is it possible to be more clear about this section please ?

[dumblob]

Without trying I guess the problem is #include "a.v" (which every C programmer knows does "plain text include" and therefore it is clear that the C compiler can not compile a .v file with V syntax inside 😉). Try to include the by-V-compiler generated .c file and that shall work more or less.

[JalonSolov]

There are several ways to do what you want. You could have V generate C code, then call it from your other C file.

v -o a.c a.v
gcc b.c a.c

Or you could create a shared lib with V then link your C code with it

v -shared a.v
gcc b.c a.so

etc.

[JalonSolov]

Just remove the #include "a.v" line from b.c before you try. Depending on your C compiler, you may need to include a prototype in b.c for the function in a.v.

[nicolasventer]

I succeed to generate the C file with v -o a.c a.v -shared.
But when after I run gcc -c a.c I have the error:
VERROR_MESSAGE Header file <gc.h>, needed for module `builtin` was not found. Please install the corresponding development headers..
How can I install the corresponding development headers ?

[JalonSolov]

Install the libgc package for your system.

[nicolasventer]

Thanks for the reply.
I executed on Linux (Ubuntu): sudo apt-get install -y libgc-dev
And then I compile with gcc a.c b.c -lgc and it works! 👍

[mnuccioarpae]

Try this.

a.v:

module a

[export: 'my_custom_c_name']
fn foo() {
        println("foo")
}

b.c:

void my_custom_c_name();

int main()
{
        my_custom_c_name();
}

$ v -shared a.v
$ gcc b.c a.so
$ LD_LIBRARY_PATH=. ./a.out
foo

[nicolasventer]

Thanks everyone for all your replies.

I made a pull request that sum up the information you gave.

Here is the link : #15844

[0xAvinash]

On my macbook I needed to use: v -o some.c -cross some.v and compile the some.c file with gcc -o some some.c now you can run ./some output file.

[0xAvinash]

I think, I posted my solution in wrong thread.