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Re: solved Re: obtaining a c value from a perl script

From fred flintstone <fred@server.invalid>
Newsgroups comp.lang.c
Subject Re: solved Re: obtaining a c value from a perl script
Date 2017-05-10 01:03 -0700
Message-ID <enfvqcFqdfoU1@mid.individual.net> (permalink)
References (6 earlier) <01776996-90c9-4721-ab10-ab6149d828fa@googlegroups.com> <enat1jFqnvhU1@mid.individual.net> <32cc7dc7-4419-44a3-b0f5-50d1a7f0d400@googlegroups.com> <endhaeFbvqgU1@mid.individual.net> <874lwuazve.fsf@bsb.me.uk>

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On 05/09/2017 07:06 AM, Ben Bacarisse wrote:
> fred flintstone <fred@server.invalid> writes:
>
>> On 05/08/2017 04:39 AM, Malcolm McLean wrote:
> <snip>
>>> When declaring a function that accepts a function pointer in C, it is good
>>> practice to always add a void * as a parameter, and accept a void * to pass
>>> back.
> <snip>
>> Thanks for your elaboration, malcolm, it prompted the literal solution
>> of this thread.
>
> You may have misunderstood.  Your code has no functions that meet the
> criteria in Malcolm's remark: "a function that accepts a function
> pointer".
>
> <snip>
>> This program was called with "./jup".
>> Value from perl : 2457987.259259
>> Can't use an undefined value as a SCALAR reference at 3.neptune.pl line 102.
>> $
>>
>> #include <stdio.h>
>> #include <stdlib.h>
>>
>> int main (int argc, char *argv[])
>> {
>>   double d;
>>   printf ("This program was called with \"%s\".\n",argv[0]);
>>   if (argc == 2)
>>     {
>>        d = atof(argv[1]);
>>        printf("Value from perl : %f\n", d );
>>        char array[20] = "Hello from C";
>>        return ( array );
>
> You compiler should have told you that this was, at best, dodgy.  main
> is an int valued function and 'array' is not an int.
>
> Just as you are choosing to pass the number to your program as a string,
> you need to get the results back as a string.  To do that you *print*
> the result:
>
>   #include <stdio.h>
>   #include <stdlib.h>
>
>   int main (int argc, char *argv[])
>   {
>        if (argc == 2)
>             printf("%f\n", atof(argv[1]) / 2);
>        else fprintf(stderr,  "Error: 1 argument expected.\n");
>        return 0;
>   }
>
> and in Perl you collect this output for later use:
>
>   $ perl -e 'print "C program returns ", `./jup 22`;'
>   C program returns 11.000000
>
> <snip>
>

Thanks, ben,

[driver]
echo 'after compilation avec warnings, output is'
gcc -Wall -Wextra -o banana 3.receive.c


$ ./banana
Error: 1 argument expected.
$ ./banana 34.55666666
34.556667
$ cat 3.receive.c
#include <stdio.h>
#include <stdlib.h>

int
main (int argc, char *argv[])
{
   if (argc == 2)
     printf ("%f\n", atof (argv[1]) / 1.0);
   else
     fprintf (stderr, "Error: 1 argument expected.\n");
   return 0;
}
$

I'm curious whether a C compiler can decide better not to do the 
division at all....
-- 
fred

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obtaining a c value from a perl script fred flintstone <fred@server.invalid> - 2017-04-30 04:36 -0700
  Re: obtaining a c value from a perl script Noob <root@127.0.0.1> - 2017-04-30 14:48 +0200
    Re: obtaining a c value from a perl script fred flintstone <fred@server.invalid> - 2017-05-01 02:25 -0700
      Re: obtaining a c value from a perl script Keith Thompson <kst-u@mib.org> - 2017-05-01 08:46 -0700
        Re: obtaining a c value from a perl script fred flintstone <fred@server.invalid> - 2017-05-03 02:12 -0700
          Re: obtaining a c value from a perl script Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-03 11:48 +0100
  Re: obtaining a c value from a perl script Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-04-30 16:16 +0100
    Re: obtaining a c value from a perl script fred flintstone <fred@server.invalid> - 2017-05-01 04:18 -0700
      Re: obtaining a c value from a perl script Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-01 13:41 +0100
        Re: obtaining a c value from a perl script Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-05-03 05:10 -0700
          Re: obtaining a c value from a perl script Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-03 15:00 +0100
          Re: obtaining a c value from a perl script Keith Thompson <kst-u@mib.org> - 2017-05-03 08:55 -0700
            Re: obtaining a c value from a perl script Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-05-03 09:02 -0700
              Re: obtaining a c value from a perl script Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-03 17:22 +0100
                Re: obtaining a c value from a perl script fred flintstone <fred@server.invalid> - 2017-05-08 01:43 -0700
                Re: obtaining a c value from a perl script Keith Thompson <kst-u@mib.org> - 2017-05-08 09:06 -0700
                Re: obtaining a c value from a perl script fred flintstone <fred@server.invalid> - 2017-05-09 00:35 -0700
                Re: obtaining a c value from a perl script David Brown <david.brown@hesbynett.no> - 2017-05-09 13:59 +0200
              Re: obtaining a c value from a perl script fred flintstone <fred@server.invalid> - 2017-05-08 02:45 -0700
                Re: obtaining a c value from a perl script Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-05-08 04:39 -0700
                solved Re: obtaining a c value from a perl script fred flintstone <fred@server.invalid> - 2017-05-09 02:43 -0700
                Re: solved Re: obtaining a c value from a perl script Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-09 15:06 +0100
                Re: solved Re: obtaining a c value from a perl script fred flintstone <fred@server.invalid> - 2017-05-10 01:03 -0700
                Re: solved Re: obtaining a c value from a perl script Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-10 11:18 +0100
                Re: solved Re: obtaining a c value from a perl script fred flintstone <fred@server.invalid> - 2017-05-12 02:26 -0700
                Re: solved Re: obtaining a c value from a perl script Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-12 11:51 +0100
                Re: solved Re: obtaining a c value from a perl script fred flintstone <fred@server.invalid> - 2017-05-12 03:49 -0700
                Re: solved Re: obtaining a c value from a perl script Manfred <invalid@invalid.add> - 2017-05-10 23:21 +0200
                Re: solved Re: obtaining a c value from a perl script Keith Thompson <kst-u@mib.org> - 2017-05-10 16:23 -0700
                Re: solved Re: obtaining a c value from a perl script Robert Wessel <robertwessel2@yahoo.com> - 2017-05-11 15:57 -0500
                Re: solved Re: obtaining a c value from a perl script Jerry Stuckle <jstucklex@attglobal.net> - 2017-05-11 18:57 -0400
                Re: solved Re: obtaining a c value from a perl script Robert Wessel <robertwessel2@yahoo.com> - 2017-05-11 18:38 -0500
                Re: solved Re: obtaining a c value from a perl script Robert Wessel <robertwessel2@yahoo.com> - 2017-05-11 18:46 -0500
                Re: solved Re: obtaining a c value from a perl script Jerry Stuckle <jstucklex@attglobal.net> - 2017-05-11 21:11 -0400
                Re: solved Re: obtaining a c value from a perl script Robert Wessel <robertwessel2@yahoo.com> - 2017-05-12 01:51 -0500
                Re: solved Re: obtaining a c value from a perl script Jerry Stuckle <jstucklex@attglobal.net> - 2017-05-14 23:49 -0400
                Re: obtaining a c value from a perl script Tim Rentsch <txr@alumni.caltech.edu> - 2017-05-09 07:46 -0700
            Re: obtaining a c value from a perl script mark.bluemel@gmail.com - 2017-05-03 09:06 -0700
              Re: obtaining a c value from a perl script gazelle@shell.xmission.com (Kenny McCormack) - 2017-05-03 17:02 +0000
              Re: obtaining a c value from a perl script fred flintstone <fred@server.invalid> - 2017-05-08 01:51 -0700
      Re: obtaining a c value from a perl script Manfred <noname@invalid.add> - 2017-05-04 18:21 +0200
        Re: obtaining a c value from a perl script fred flintstone <fred@server.invalid> - 2017-05-08 03:52 -0700
          Re: obtaining a c value from a perl script Jerry Stuckle <jstucklex@attglobal.net> - 2017-05-08 08:38 -0400
          Re: obtaining a c value from a perl script Keith Thompson <kst-u@mib.org> - 2017-05-08 09:14 -0700
          Re: obtaining a c value from a perl script "James R. Kuyper" <jameskuyper@verizon.net> - 2017-05-08 12:17 -0400
            Re: obtaining a c value from a perl script Keith Thompson <kst-u@mib.org> - 2017-05-08 09:26 -0700
              Re: obtaining a c value from a perl script jameskuyper@verizon.net - 2017-05-08 11:02 -0700
                Re: obtaining a c value from a perl script Keith Thompson <kst-u@mib.org> - 2017-05-08 11:39 -0700
              Re: obtaining a c value from a perl script Tim Rentsch <txr@alumni.caltech.edu> - 2017-05-09 07:16 -0700
                Re: obtaining a c value from a perl script Keith Thompson <kst-u@mib.org> - 2017-05-09 08:18 -0700
                Re: obtaining a c value from a perl script fred flintstone <fred@server.invalid> - 2017-05-10 00:29 -0700
                Re: obtaining a c value from a perl script Tim Rentsch <txr@alumni.caltech.edu> - 2017-05-10 05:26 -0700
            Re: obtaining a c value from a perl script Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-08 18:20 +0100

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