2017. november 6., hétfő 2:11:48 UTC+1 időpontban Chun Zhang a következőt
írta:
>
> Hi, All,
>
> I am trying to read a configuration file using Viper, the config file is a
> very simple json file with one line
> {
> "device" : "eth1"
> }
>
> I use the following line to read it
>
> device := viper.GetString("device")
>
>
> then passing this var further into a C library with swig generated api as
> arg2
>
> itc := device //Need to update if there is more devices
> libpi.PI_init_global_config(1, &itc)
>
> func PI_init_global_config(arg1 int, arg2 *string) {
>
>
>
> I can retrieve the correct value, and can verify that var device does
> have eth1 as the value when printf it. I even did the compare of device ==
> "eth1", and the result is true.
>
> However, when passing this device var to the PI_init_gloable_config API, I
> got code crashed with the following error
>
> *panic: runtime error: cgo argument has Go pointer to Go pointer*
>
>
The value you pass to C must not have a pointer which points to a Go
pointer.
What are you passing to libpi.PI_init_global_config ?
I think "device" is already a *string, so &itc is a **string - try
libpi.PI_init_global_config(device).
(I assume libpi does some conversion, as the proper way to pass a string ot
C (*char) is to convert the string to *char with cs:=C.CString(*device) and
later C.free(unsafe.Pointer(cs)) it).
>
> If instead of reading this file from configuration json, I hardcode it in
> the code as
>
> device := "eth1"
>
> then there is no issue at all. If I read this variable using Flag from
> command line, like
>
> flag.StringVar(&device, "Device", "eth1", "NIC to Listen")
>
>
> there was no problem either.
>
>
>
> Can anybody please enlighten me what's the difference? Why this error is
> triggered? I googled quite a bit, but it does not seem to help. I have go
> 1.8.3 installed.
>
> Thanks,
> Chun
>
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