Beefy Boxes and Bandwidth Generously Provided by pair Networks
Perl Monk, Perl Meditation
 
PerlMonks  

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??

Given that weekends are typically slower than through the week, I thought I'd ask for a quick code review of those who understand the perl internals. This is my real first attempt at doing anything regarding manipulating and managing perl data types in C/XS, and am just wondering if what I've got below is reasonable, sane and safe, or if there are better ways to do it.

Instead of passing an integer into the C function then doing a bunch of bit shifting to get out the required number of bytes, I wanted to pass in an array reference so that the number of bytes can be dynamic (otherwise with an int, I'm limited to a maximum of four bytes in a call to testing()).

use warnings; use strict; use Inline 'C'; my $channel = 0; my @bytes = (0x00, 0x01, 0x02, 0x03); testing($channel, \@bytes, 4); __END__ __C__ int testing(int channel, SV* byte_ref, int len){ if (channel != 0 && channel != 1){ croak("channel param must be 0 or 1\n"); } if (! SvROK(byte_ref) || SvTYPE(SvRV(byte_ref)) != SVt_PVAV){ croak("not an aref\n"); } AV* bytes = (AV*)SvRV(byte_ref); int num_bytes = av_len(bytes) + 1; if (len != num_bytes){ croak("$len param != elem count\n"); } unsigned char buf[num_bytes]; int i; for (i=0; i<len; i++){ SV** elem = av_fetch(bytes, i, 0); buf[i] = (int)SvNV(*elem); } /* * here, I'll be passing the char buffer and len * to an external C function. For display, I'll * just print the elements (the return is from ioctl()) * * if ((spiDataRW(channel, buf, len) < 0){ * croak("failed to write to the SPI bus\n"); * } */ int x; for (x=0; x<len; x++){ printf("%d\n", buf[x]); } }

In reply to Is this a sane/safe way to pass an aref into a C function? by stevieb

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":



  • Are you posting in the right place? Check out Where do I post X? to know for sure.
  • Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
    <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
  • Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
  • Want more info? How to link or or How to display code and escape characters are good places to start.
Log In?
Username:
Password:

What's my password?
Create A New User
Domain Nodelet?
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others wandering the Monastery: (6)
As of 2022-08-18 14:18 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    No recent polls found

    Notices?