| Re: String array from C [message #65001] |
Fri, 06 February 2009 08:58 |
Allan Whiteford
Messages: 117
Registered: June 2006
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Senior Member |
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Robbie wrote:
> I've had some problems dealing with string arrays which have been
> generated from a C program.
>
> If I try LONG(str) or FIX(str) I will find that there are extra
> characters which get processed, yet I don't see them when I try PRINT
> and HELP.
> I can workaround the problem by using LONG(STRMID(0,str)) and FIX
> (STRMID(0,str)).
>
> Perhaps I have string processing mixed up. But, I thought that
> IDL_StrEnsureLength took are of everything. I've changed my C code and
> the problem has gone away, but I still don't understand why.
>
> The original C code was:
> char* v = PQgetvalue(Res,row,col);
> int vl = strlen(v);
> IDL_StrEnsureLength(&(pisArray[i]), vl);
> strncpy(pisArray[i].s, v, vl);
>
> The new C code is:
> char* v = PQgetvalue(Res,row,col);
> int vl = strlen(v);
> IDL_StrEnsureLength(&(pisArray[i]), vl+1);
> strncpy(pisArray[i].s, v, vl+1);
> pisArray[i].slen = vl;
>
> Thanks
> Robbie
Hi,
You're supposed to use:
IDL_StrStore
to copy a string from C-land to IDL-land. If you don't then you'll end
up in a whole world of hurt.
This will take care of setting the slen part of the IDL_STRING
structure. You can't rely on the null termination character from C
meaning anything to IDL.
Also, if you write directly into the .s pointer (which points to the
actual string) there is a chance you'll overwrite totally unrelated
strings. For efficiency, if you have two string variables set to the
same value then IDL will (sometimes!) only store the data once in memory
and point both the .s pointers at the same place. IDL keeps track of
when the pointers need to point to different places when one of the
strings changes (as does IDL_StrStore) but if you mess with the data
yourself directly then you can end up modifying variables you never
intended to.
Thanks,
Allan
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