From: G DOT DegliEsposti AT ads DOT it
To: Junior System Administrator <pete AT restall DOT net>
cc: djgpp AT delorie DOT com
Message-ID: <C125660A.00277622.00@vega.ads.it>
Date: Wed, 20 May 1998 09:38:38 +0200
Subject: Re: Please help me :-)
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>Hi.  I'm having a problem with some C code to extract tokens from a
string.  The
There are some problems caused by different data types between formal
parameters
and actual parameters.

You have stumbled into a classical beginner problem concerning array and
pointers relationship...

>code looks something like:
[...]
>void     str_gettokens(char *string, char *buf[], int *tokens);
Here you declare buf as an array of pointers to strings, ie, something like
this:

4 bytes: buf[0] -- points to ---> "first string" somewhere else in memory
4 bytes: buf[1] -- points to ---> "second string" somewhere else in memory
...
4 bytes: buf[N] -- points to ---> "last string" somewhere else in memory

[...]
>    char token_array[16][255];    /* Max 16 tokens, 255 chars each */
Here you define token_array as an array of arrays of char, ie:

1 byte: t_a[0][0]
1 byte: t_a[0][1]
1 byte: t_a[0][2]
...
1 byte: t_a[0][254]
...
1 byte: t_a[15][255]

[...]
>    str_gettokens(cmd_string, token_array, &tokens);
[...]
>         sprintf(buf[(*tokens)++], "%.*s", i, p);
And here the problems comes out: the argument 'buf' is declared as an array
of pointers, this means that first 4 bytes of buf area interpreted as a
pointer
to the string, and not as the first 4 chars of the string, accordingly with
the declaration of token_array.

[...]
>When I compile this program, I get a 'suspicious pointer conversion' error
from
>DJGPP (line that calls 'str_gettokens()').  When I run the compiled EXE,
the
>program crashes.  However, if I compile and run the program minus the line
That's because there is an access to a non valid pointer.

>that 'sprintf()'s the token into the buffer, the program runs OK (but
obviously
>without putting anything into 'buf').  I've never had to do anything which
>involves passing arrays of character arrays to a function before, and now
I'm
>a bit lost ;-).  Can anyone help ???

You have to either declare buf the same type of token_array, or can build
token_array accordingly to buf, like this:

char *token_array[16]; /* consinstent with argument buf */
for(i=0; i<16;i++)
  token_array[i] = (char *)malloc(256); /* element points to a 256 chars
string */

As a side note, I point out that your problem was a general C question, and
not djgpp specific, so it is a little off topic here. Beginners are of
course due
answers, but try to post other C questions to comp.lang.c in the future :-)

And, before someone else from the ng tells you, the ANSI standard requires
main()
to return int and not void. :-)

ciao
  Giacomo