Re: [netcdfgroup] NC_STRING and NC_CHAR ... How to read strings?

• To: "netcdfgroup@xxxxxxxxxxxxxxxx" <netcdfgroup@xxxxxxxxxxxxxxxx>
• Subject: Re: [netcdfgroup] NC_STRING and NC_CHAR ... How to read strings?
• From: Panov Sergey <sergey.panov@xxxxxxxxxxx>
• Date: Thu, 28 Feb 2019 05:11:16 +0000
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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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• Follow-Ups:
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    • From: Dennis Heimbigner

• References:
  • [netcdfgroup] NC_STRING and NC_CHAR ... How to read strings?
    • From: Panov Sergey