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Groups > comp.lang.c > #112749

Re: Warning: assignment from incompatible pointer type

From Lew Pitcher <lew.pitcher@digitalfreehold.ca>
Newsgroups comp.lang.c
Subject Re: Warning: assignment from incompatible pointer type
Followup-To comp.lang.c
Date 2017-06-20 19:46 -0400
Organization The Pitcher Digital Freehold
Message-ID <oicbug$29r$1@dont-email.me> (permalink)
References <Mlc2B.23027$xk.11193@fx39.iad> <8760fqbjrr.fsf@bsb.me.uk> <oic978$qkf$3@dont-email.me>

Followups directed to: comp.lang.c

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DFS wrote:

> On 6/20/2017 2:23 PM, Ben Bacarisse wrote:
>> DFS <nospam@dfs.com> writes:
>> 
>>> Why am I getting this warning?
>>>
>>>
>>> char groups[100][20];
>>> int g=0;
>>> sprintf(uname,"%s",data[0][1]);
>>> strcpy(groups[g],uname);
>>>
>>> for(i=1;i<lines;i++)
>>> {
>>> sprintf(dname,"%s",data[i][1]);
>>> if (iteminarray(groups,g,dname)!=0)    //THROWS WARNING HERE
>>> {
>>> strncpy(groups[g++],dname,strlen(dname));
>> 
>> Take care.  This may result in no terminating null (and it wastes time
>> filling with zeros).  If you want a string (as you seem to since you
>> test with strcmp not strncmp) use the proper string function to copy
>> the data about as you do 7 lines up.
> 
> Done.
> 
> Also, something "strange" happens on that line:
> 
> strncpy(groups[g++],dname,strlen(dname));
> 
> g++ doesn't increment g before adding dname to groups.

Of course not,
  g++
is a postfix expression; the value used in the groups[] subscript 
calculation will be the value of g prior to the increment. That's what g++ 
means.

If you wanted g incremented /first/, you should have used
  ++g
as in
  strncpy(groups[++g],dname,strlen(dname));

> The initial
> value I added to groups[0] is overwritten.
> 
> You have to do g++; before the string copy for it to work the way you
> expect it to work.
> 
> g++;
> strncpy(groups[g],dname,strlen(dname));
> 
> Is that odd to you?

Not at all. That's how a postfix increment is supposed to work.

[snip]
-- 
Lew Pitcher
"In Skills, We Trust"
PGP public key available upon request

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Warning: assignment from incompatible pointer type DFS <nospam@dfs.com> - 2017-06-20 12:48 -0400
  Re: Warning: assignment from incompatible pointer type bartc <bc@freeuk.com> - 2017-06-20 18:08 +0100
    Re: Warning: assignment from incompatible pointer type DFS <nospam@dfs.com> - 2017-06-21 09:32 -0400
      Re: Warning: assignment from incompatible pointer type scott@slp53.sl.home (Scott Lurndal) - 2017-06-21 13:48 +0000
  Re: Warning: assignment from incompatible pointer type Richard Heathfield <rjh@cpax.org.uk> - 2017-06-20 18:15 +0100
    Re: Warning: assignment from incompatible pointer type DFS <nospam@dfs.com> - 2017-06-20 18:00 -0400
      Re: Warning: assignment from incompatible pointer type "James R. Kuyper" <jameskuyper@verizon.net> - 2017-06-20 18:47 -0400
        Re: Warning: assignment from incompatible pointer type bartc <bc@freeuk.com> - 2017-06-21 00:10 +0100
        Re: Warning: assignment from incompatible pointer type DFS <nospam@dfs.com> - 2017-06-20 19:56 -0400
  Re: Warning: assignment from incompatible pointer type "James R. Kuyper" <jameskuyper@verizon.net> - 2017-06-20 13:23 -0400
    Re: Warning: assignment from incompatible pointer type DFS <nospam@dfs.com> - 2017-06-20 18:59 -0400
  Re: Warning: assignment from incompatible pointer type Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-20 19:23 +0100
    Re: Warning: assignment from incompatible pointer type DFS <nospam@dfs.com> - 2017-06-20 18:59 -0400
      Re: Warning: assignment from incompatible pointer type Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2017-06-20 19:46 -0400
      Re: Warning: assignment from incompatible pointer type Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-21 02:05 +0100
        Re: Warning: assignment from incompatible pointer type DFS <nospam@dfs.com> - 2017-06-20 21:37 -0400
          Re: Warning: assignment from incompatible pointer type Richard Heathfield <rjh@cpax.org.uk> - 2017-06-21 09:25 +0100
          Re: Warning: assignment from incompatible pointer type David Brown <david.brown@hesbynett.no> - 2017-06-21 13:35 +0200
            Re: Warning: assignment from incompatible pointer type DFS <nospam@dfs.com> - 2017-06-21 22:30 -0400
              Re: Warning: assignment from incompatible pointer type Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-22 11:03 +0100
              Re: Warning: assignment from incompatible pointer type bartc <bc@freeuk.com> - 2017-06-22 11:10 +0100
                Re: Warning: assignment from incompatible pointer type bartc <bc@freeuk.com> - 2017-06-22 11:42 +0100
                Re: Warning: assignment from incompatible pointer type David Brown <david.brown@hesbynett.no> - 2017-06-22 13:49 +0200
                Re: Warning: assignment from incompatible pointer type bartc <bc@freeuk.com> - 2017-06-22 14:40 +0100
                Re: Warning: assignment from incompatible pointer type bartc <bc@freeuk.com> - 2017-06-22 17:00 +0100
                Re: Warning: assignment from incompatible pointer type David Brown <david.brown@hesbynett.no> - 2017-06-22 20:08 +0200
                Re: Warning: assignment from incompatible pointer type DFS <nospam@dfs.com> - 2017-06-22 15:46 -0400
                Re: Warning: assignment from incompatible pointer type Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-22 14:00 +0100
                Re: Warning: assignment from incompatible pointer type bartc <bc@freeuk.com> - 2017-06-22 14:38 +0100
                Re: Warning: assignment from incompatible pointer type Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-22 17:26 +0100
                Re: Warning: assignment from incompatible pointer type Keith Thompson <kst-u@mib.org> - 2017-06-22 10:21 -0700
                Re: Warning: assignment from incompatible pointer type bartc <bc@freeuk.com> - 2017-06-22 18:26 +0100
                Re: Warning: assignment from incompatible pointer type David Brown <david.brown@hesbynett.no> - 2017-06-22 20:41 +0200
                Re: Warning: assignment from incompatible pointer type Richard Heathfield <rjh@cpax.org.uk> - 2017-06-22 19:59 +0100
                Re: Warning: assignment from incompatible pointer type Keith Thompson <kst-u@mib.org> - 2017-06-22 12:28 -0700
          Re: Warning: assignment from incompatible pointer type Jerry Stuckle <jstucklex@attglobal.net> - 2017-06-21 09:49 -0400
            Re: Warning: assignment from incompatible pointer type DFS <nospam@dfs.com> - 2017-06-21 10:36 -0400
              Re: Warning: assignment from incompatible pointer type Jerry Stuckle <jstucklex@attglobal.net> - 2017-06-21 14:15 -0400
          Re: Warning: assignment from incompatible pointer type Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-21 15:10 +0100

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