CGO - convert a c.char array to string

[nicolas...@yahoo.fr]

Hello

i have a little problem to convert a C char array to a string array in golang.

https://community.bistudio.com/wiki/Extensions

func RVExtensionArgs(output *C.char, outputsize C.size_t, input *C.char, argv **C.char, argc C.size_t) {
    temp := fmt.Sprintf("Hello %s %d %s!", C.GoString(input), argc,  C.GoString(*argv)

    // return to C program, the string
    result := C.CString(temp)
    defer C.free(unsafe.Pointer(result))
    var size = C.strlen(result) + 1
    if size > outputsize {
        size = outputsize
    }
    C.memmove(unsafe.Pointer(output), unsafe.Pointer(result), size)
}

I did this code only to print the content of argv for test purpose. This code only return the first string of argv array.

Do you know a standard method to iterate & convert all the argv array in one golang string array  ?

[Jan Mercl]

On Sun, Aug 5, 2018 at 12:05 PM nicolas_boiteux via golang-nuts <golan...@googlegroups.com> wrote:

> Do you know a standard method to iterate & convert all the argv array in one golang string array ?

Something like (not tested):

var a []string

for p := argv; *p != nil; p = (**C.char)(unsafe.Pointer(uintptr(p)+unsafe.Sizeof(*p))) {

        a = append(a, C.GoSting(*p))

}

--

-j

[nicolas...@yahoo.fr]

it returns :

.\armago_x64.go:19: cannot convert p (type **_Ctype_char) to type uintptr

I am a little lost with this conversion, I do not understand how the iterator should work. I hope there was a simple command like GoString to do it.

[Jan Mercl]

On Sun, Aug 5, 2018 at 12:29 PM nicolas_boiteux via golang-nuts <golan...@googlegroups.com> wrote:

> it returns :
>
> .\armago_x64.go:19: cannot convert p (type **_Ctype_char) to type uintptr

Ok, this time bit more tested

jnml@4670:~/tmp> cat main.c

#include <stdio.h>

int main(int argc, char **argv) {

char **p;

for (p = argv; *p != 0; p++) {

printf("%s\n", *p);

}

}

jnml@4670:~/tmp> ccgo main.c && ./a.out abc def ghi

./a.out

abc

def

ghi

jnml@4670:~/tmp> ccgo -o main.go main.c

jnml@4670:~/tmp> cat main.go

// Code generated by 'ccgo -o main.go main.c', DO NOT EDIT.

// +build linux,amd64

package main

import (

"math"

"os"

"unsafe"

"github.com/cznic/crt"

)

const (

null = uintptr(0)

)

var (

_ = math.Pi

_ = os.DevNull

_ = unsafe.Pointer(null)

nz32 float32

nz64 float64

)

func init() { nz32 = -nz32 }

func init() { nz64 = -nz64 }

func alloca(p *[]uintptr, n int) uintptr   { r := crt.MustMalloc(n); *p = append(*p, r); return r }

func preinc(p *uintptr, n uintptr) uintptr { *p += n; return *p }

func main() {

psz := unsafe.Sizeof(uintptr(0))

argv := crt.MustCalloc((len(os.Args) + 1) * int(psz))

p := argv

for _, v := range os.Args {

*(*uintptr)(unsafe.Pointer(p)) = crt.CString(v)

p += psz

}

a := os.Environ()

env := crt.MustCalloc((len(a) + 1) * int(psz))

p = env

for _, v := range a {

*(*uintptr)(unsafe.Pointer(p)) = crt.CString(v)

p += psz

}

*(*uintptr)(unsafe.Pointer(Xenviron)) = env

X_start(crt.NewTLS(), int32(len(os.Args)), argv)

}

// linking main.o

// X__ccgo_va_end *void, escapes: true, builtin.h:36:6

var X__ccgo_va_end = bss + 0

// X__ccgo_va_start *void, escapes: true, builtin.h:37:6

var X__ccgo_va_start = bss + 8

// Xmain is defined at main.c:3:5

func Xmain(tls crt.TLS, _argc int32, _argv uintptr /* **int8 */) (r int32) {

var _p uintptr // **int8

_p = _argv

_1:

if (*(*uintptr)(unsafe.Pointer(_p))) == 0 {

goto _3

}

crt.Xprintf(tls, ts+0 /* "%s\n" */, *(*uintptr)(unsafe.Pointer(_p)))

_p += 8

goto _1

_3:

return r

}

// linking crt0.o

// X__stdfiles [3]uintptr, escapes: true, crt0.c:3:15

var X__stdfiles = bss + 16

// Xenviron **int8, escapes: true, crt0.c:4:6

var Xenviron = bss + 40

// Xstdin *void, escapes: true, crt0.c:5:6

var Xstdin = bss + 48 // pointer to void

func init() { *(*uintptr)(unsafe.Pointer(Xstdin)) = X__stdfiles }

// Xstdout *void, escapes: true, crt0.c:5:31

var Xstdout = bss + 56 // pointer to void

func init() { *(*uintptr)(unsafe.Pointer(Xstdout)) = X__stdfiles + 8 }

// Xstderr *void, escapes: true, crt0.c:5:57

var Xstderr = bss + 64 // pointer to void

func init() { *(*uintptr)(unsafe.Pointer(Xstderr)) = X__stdfiles + 16 }

// X_start is defined at crt0.c:7:6

func X_start(tls crt.TLS, _argc int32, _argv uintptr /* **int8 */) {

crt.X__register_stdfiles(tls, *(*uintptr)(unsafe.Pointer(Xstdin)), *(*uintptr)(unsafe.Pointer(Xstdout)), *(*uintptr)(unsafe.Pointer(Xstderr)), Xenviron)

crt.X__builtin_exit(tls, Xmain(tls, _argc, _argv))

}

func init() { *(*uintptr)(unsafe.Pointer(Xstdin)) = X__stdfiles }

func init() { *(*uintptr)(unsafe.Pointer(Xstdout)) = X__stdfiles + 8 }

func init() { *(*uintptr)(unsafe.Pointer(Xstderr)) = X__stdfiles + 16 }

var (

bss     = crt.BSS(&bssInit[0])

bssInit [72]byte

ts      = crt.TS("%s\n\x00")

)

jnml@4670:~/tmp> 

I hope you can extract the code for your case from the above mechanically produced Go code. Note that ccgo uses untrptrs instead of normal pointers but that should be an easy adjustment, I hope.

--

-j

[nicolas...@yahoo.fr]

not sure to understand cause the iteration in your example is done on os interface from golang not from c char array :(

[Miki Tebeka]

Hi,

 

i have a little problem to convert a C char array to a string array in golang

Maybe something like

var offset = unsafe.Sizeof(uintptr(0))

func argv2go(argv **C.char) []string {
    var out []string
    for *argv != nil {
        out = append(out, C.GoString(*argv))
        argv = (**C.char)(unsafe.Pointer(uintptr(unsafe.Pointer(argv)) + offset))
    }

    return out
}

 

[Jan Mercl]

On Sun, Aug 5, 2018 at 2:50 PM nicolas_boiteux via golang-nuts <golan...@googlegroups.com> wrote:

> not sure to understand cause the iteration in your example is done on os interface from golang not from c char array :(

Not sure what you mean by 'os interface'. Here's the part that iterates **C.char, except pointers are transformed to uintptrs. Other that that it's what you're, I think, after

// Xmain is defined at main.c:3:5

func Xmain(tls crt.TLS, _argc int32, _argv uintptr /* **int8 */) (r int32) {

var _p uintptr // **int8

_p = _argv

_1:

if (*(*uintptr)(unsafe.Pointer(_p))) == 0 {

goto _3

}

crt.Xprintf(tls, ts+0 /* "%s\n" */, *(*uintptr)(unsafe.Pointer(_p)))

_p += 8

goto _1

_3:

return r

}

Manually converting (untested again):

func foo(argv **C.char) []string {

        var a []string

        for p := argv; *p != nil; *(*uintptr)(unsafe.Pointer(p)) += unsafe.Sizeof(*p) {

                a = append(a, GoString(*p))

        }

        rerurn a

}

--

-j

[nicolas...@yahoo.fr]

Miki & Jan thanks

i tested the both methods. Dll compiles normaly, but program crash.

With Miki code the first time, i run the code, i saw that string array contains also other characters that not come from argv.

[nicolas...@yahoo.fr]

i found another thing.

func RVExtensionArgs(output *C.char, outputsize C.size_t, input *C.char, argv **C.char, argc C.int) {
    var offset = unsafe.Sizeof(uintptr(0))
    var out []string
    limit := *(*int)(unsafe.Pointer(&argc))
    if limit < 1000 {
        for index := 0; index < limit; index++ {

            out = append(out, C.GoString(*argv))
            argv = (**C.char)(unsafe.Pointer(uintptr(unsafe.Pointer(argv)) + offset))
        }
    }

    temp := fmt.Sprintf("Hello %s %d %s!", C.GoString(input), limit,  out)

    // Return a result to Arma

    result := C.CString(temp)
    defer C.free(unsafe.Pointer(result))
    var size = C.strlen(result) + 1
    if size > outputsize {
        size = outputsize
    }
    C.memmove(unsafe.Pointer(output), unsafe.Pointer(result), size)

}Saisissez le code ici...

it seems there is also a bug in the main program cause the argc variable, the first execution time contains a memory adress instead of int

[nicolas...@yahoo.fr]

thanks you, the A3 community finaly help me to solve the last problem

    for index := C.int(0); index < argc; index++ {


        out = append(out, C.GoString(*argv))
        argv = (**C.char)(unsafe.Pointer(uintptr(unsafe.Pointer(argv)) + offset))
    }




I dont really understand why but it seems there was a problem with my casting method with unsafe

*(*int)(unsafe.Pointer(limit)

[Ian Lance Taylor]

On Sun, Aug 5, 2018 at 10:29 PM, nicolas_boiteux via golang-nuts
<golan...@googlegroups.com> wrote:
>
> thanks you, the A3 community finaly help me to solve the last problem
>
> for index := C.int(0); index < argc; index++ {
> out = append(out, C.GoString(*argv))
> argv = (**C.char)(unsafe.Pointer(uintptr(unsafe.Pointer(argv)) +
> offset))
> }
>
> I dont really understand why but it seems there was a problem with my
> casting method with unsafe
>
> *(*int)(unsafe.Pointer(limit)

See https://golang.org/pkg/unsafe for the exact ways that you are
permitted to use unsafe.Pointer.

Ian

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[nicolas...@yahoo.fr]

yes i used the code from this page:

func Float64bits(f float64) uint64 {
	return *(*uint64)(unsafe.Pointer(&f))
}

adapted to my use case

*(*int)(unsafe.Pointer(limit)

[Ian Lance Taylor]

On Mon, Aug 6, 2018 at 11:34 PM, nicolas_boiteux via golang-nuts
<golan...@googlegroups.com> wrote:
>
> yes i used the code from this page:
>
> func Float64bits(f float64) uint64 {
> return *(*uint64)(unsafe.Pointer(&f))
> }
>
> adapted to my use case
>
> *(*int)(unsafe.Pointer(limit)

As the docs say, that is only permissible when T2 is no larger than T1
and the two share an equivalent memory layout. In your case T2 is the
Go type `int` and T1 is the C type `int`. On 64-bit systems the C
type `int` is 32 bits and the Go type `int` is 64 bits. So T2 is
larger than T1 and your conversion is not permitted by the unsafe
rules.

Ian