On Thu, 2019-02-28 at 13:13 -0700, Dennis Heimbigner wrote:
> I think the key is your observation:
> > char buffer[20];
> > inst_var.getVar(buffer);
> > to
> > char * buffer;
> > inst_var.getVar(&buffer);
> If the variable is actually of type string (as opposed to char), then
> you need to pass a buffer into which string pointers (char*) are
> inserted
> so the getVar argument needs to be char** (your second case).
> I assume getVar is overloaded so that in the first case it is
> attempting
> to read
> a string typed variable using nc_get_vara_text.
> In the second case, you are invoking the char** overloaded getVar, so
> it is properly invoking nc_get_vara_string function.
I get it, but why I am getting a pointer to some string? If I do not
own it, why it is not const? If I own it now, am I responsible for
freeing its memory?
The netcdf-cxx4 library is C++ lib. There should be no place for
getVar(char**) and getVar(char*) in C++ lib . I expected there
getVar(string &) and getVar(vector<string> &) calls.
> =Dennis Heimbigner
> Unidata
>
>
> On 2/27/2019 10:11 PM, Panov Sergey wrote:
> > I guess it was not a segmentation fault, but a error return
> > triggering
> > C++ exception. I was able to get it to trigger a real segmentation
> > fault, but changing
> >
> > char buffer[20];
> > inst_var.getVar(buffer);
> >
> > to
> >
> > char * buffer;
> > inst_var.getVar(&buffer);
> >
> > gives me a pointer to a correct string. It is just bizarre!!! Does
> > it
> > mean I now can modify that sting and it is OK?
> >
> >
> > On Thu, 2019-02-28 at 04:31 +0000, Panov Sergey wrote:
> > > I have a very basic question -- how to read "string" variable in
> > > C or
> > > C++
> > >
> > > The ncdump tells me the variable type is "string". When I try to
> > > read
> > > it using
> > >
> > > void getVar(char* dataValues) const;
> > >
> > > function of class NcVar of netcdf-cxx4 I am hitting a
> > > segmentation
> > > fault. I am not sure why it is a segmentation fault, but it comes
> > > from
> > >
> > > ...
> > > /* No NC_CHAR conversions, you pervert! */
> > > if (var->type_info->nc_typeid != *mem_nc_type &&
> > > (var->type_info->nc_typeid == NC_CHAR || *mem_nc_type ==
> > > NC_CHAR))
> > > return NC_ECHAR;
> > > ...
> > >
> > > code in check_for_vara() function in nc4hdf.c .
> > > The var->type_info->nc_typeid is NC_STRING (12) and this check
> > > should
> > > just fail (the reading of the variable should just fail, but it
> > > "throws
> > > an exception" ... causes a segmentation fault for some reason).
> > >
> > > The stack is;
> > > check_for_vara nc4hdf.c:477
> > > nc4_get_vara nc4hdf.c:905
> > > nc4_get_vara_tc nc4var.c:1379
> > > NC4_get_vara nc4var.c:1396
> > > NC_get_vara dvarget.c:101
> > > NC_get_var dvarget.c:117
> > > nc_get_var_text dvarget.c:1020
> > > netCDF::NcVar::getVar ncVar.cpp:1340
> > > main cfradial_rd.cpp:47
> > > __libc_start_main 0x00007ffff485a413
> > > _start 0x00000000004021ee
> > >
> > > The C++ code is calling C function nc_get_var_text() to read this
> > > string which should have been normal.
> > >
> > > What am I doing wrong and what is the right way of reading
> > > "string"
> > > variables?
> > >
> > > PS. Does anyone else dislike the official C++ library API or it
> > > is
> > > just
> > > me?
> > >
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