Thanks. Can you explain the reason for this so it sticks in my head?
On Thu, 2019-12-05 at 21:03 -0700, andrey mirtchovski wrote:
> you just need to split it in two files. the cfuncs go into another
> (sorry for lack of playground link):
>
> $ go build cgo.go cfunc.go
> $ ./cgo
> Hello from stdio
>
> $ cat cgo.go
> package main
>
> /*
> #include <stdlib.h>
> extern void myprint(char *s);
> */
> import "C"
>
> import "unsafe"
>
> //export Example
> func Example() {
> cs := C.CString("Hello from stdio\n")
> C.myprint(cs)
> C.free(unsafe.Pointer(cs))
> }
>
> func main() {
> Example()
> }
> $ cat cfunc.go
> package main
>
> /*
> #include <stdio.h>
> #include <stdlib.h>
>
> void myprint(char* s) {
> printf("%s\n", s);
> }
> */
> import "C"
>
> On Thu, Dec 5, 2019 at 8:47 PM Dan Kortschak <d...@kortschak.io>
> wrote:
> >
> > I am trying to write a shared module that will be called from C,
> > but I
> > have run into a problem in using the work-around in
> > https://github.com/golang/go/wiki/cgo#the-basics for calling
> > variadic C
> > functions.
> >
> > The case that I have is more complex, but altering the example at
> > the
> > wiki demonstrates the problem; the function definition that is used
> > to
> > call on to printf appears more than once in the C code generated by
> > Cgo.
> >
> > ```
> > ~/src/github.com/kortschak/cgo $ cat cgo.go
> > package main
> >
> > /*
> > #include <stdio.h>
> > #include <stdlib.h>
> >
> > void myprint(char* s) {
> > printf("%s\n", s);
> > }
> > */
> > import "C"
> >
> > import "unsafe"
> >
> > //export Example
> > func Example() {
> > cs := C.CString("Hello from stdio\n")
> > C.myprint(cs)
> > C.free(unsafe.Pointer(cs))
> > }
> >
> > func main() {}
> > ~/src/github.com/kortschak/cgo $ go build -o cgo.so -buildmode=c-
> > shared
> > .
> > # github.com/kortschak/cgo
> > /tmp/go-build899365101/b001/_x002.o: In function `printf':
> > /usr/include/x86_64-linux-gnu/bits/stdio2.h:104: multiple
> > definition of
> > `myprint'
> > /tmp/go-build899365101/b001/_x001.o:/usr/include/x86_64-linux-
> > gnu/bits/stdio2.h:104: first defined here
> > collect2: error: ld returned 1 exit status
> > ```
> >
> > Removing the "//export Example" comment prevents this failure, but
> > then
> > obviously also loses the exported function. I have tried protecting
> > the
> > function in a #ifndef/#endif, to no avail.
> >
> > Is it reasonable for me to expect this to work? If so, what am I
> > doing
> > wrong?
> >
> > thanks
> > Dan
> >
> > --
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> > .
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