Re: API parameter lengths

[Jim Langston <jimlangston@xxxxxxxxxxxxxxxx>]

A question on this Barbara,

> #include <stdio.h>
> main(int argc, char *argv[])
> {
>    int i;
>    for (i = 1; i < argc; i++)
>    {
>       printf("arg %d %s\n", i, argv[i]);
>    }
> }
> ===> CALL pgm ('abc def ghi' 'zyx')
> arg 1 abc def ghi
> arg 2 zyx

Say the string 'abc def ghi' was in a variable.  Say that
I changed the spaces x'40' to nulls x'00'.  Then passed
them like this:

> ===> CALL pgm (&PARM1 &PARM2)

Would the C program then report this as 4 parameters or still 2?
I know that C uses null terminated strings, and am fairly sure that
the arguments are put onto the stack instead of the pointers, which
makes me think C would see 4 parameters, but I'm not sure what
argc would report.  Also, if it was 2 parameters obviously the
printf would only show the initial 'abc' anyway stopping at the null
terminator.

Regards,

Jim Langston

Me transmitte sursum, Caledoni!

bmorris@ca.ibm.com wrote:
> 
> >Date: Mon, 9 Jul 2001 10:54:23 -0500
> >From: "Alexei Pytel" <pytel@us.ibm.com>
> >
> >CALL command does not do this.
> >C PEP (program entry point) procedure does. For every main() in C,
> compiler
> >generates a PEP (you may see it if you do DSPMOD on C module). This PEP
> >procedure among other things will scan for first blank in each parameter
> >and create null-terminated string for each parameter.
> ?This makes it very difficult to pass non-character parameters to C main().
> 
> Alexei, that is not true; where did you hear that?  If you call a C program
> with a parameter of 'abc def ghi', it will get one parameter.  The
> null-termination is indeed done by the call command.
> 
> Calling a C program from another program is not difficult.  In that
> case, the C program receives the same parameters that the caller passed
> because the PEP doesn't do any processing on the parameters except to
> build the argv array from the parameters that are passed to the program.
> But it just copies the parameter pointers into the array of pointers; it
> doesn't do anything with the parameter data.
> 
> A test:
> 
> #include <stdio.h>
> main(int argc, char *argv[])
> {
>    int i;
>    for (i = 1; i < argc; i++)
>    {
>       printf("arg %d %s\n", i, argv[i]);
>    }
> }
> ===> CALL pgm ('abc def ghi' 'zyx')
> arg 1 abc def ghi
> arg 2 zyx
> 
> Barbara Morris
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