After you posted more code, I can see that:

const char *
rtlsdr_get_device_name(index)
  uint32_t index

[download]

And so this:

my $device = rtlsdr_get_device_name( $index );

returns the device name as a string, given device index (integer), and not a pointer to a rtlsdr_dev_t structure as you assumed.

Given:

int 
rtlsdr_open(dev, index)
  SDR::RTLSDR **dev
  uint32_t index

[download]

I am guessing that one must open a device by specifying the index. The function rtlsdr_open() should probably return the status as an integer and allocates internally the device, that's what I assume when it tells you to supply the double pointer for device: "Give me a memory location and I will do the internal decoration".

Here is a stand-alone C example to demonstrate this pattern:

#include <stdio.h>
#include <malloc.h>

typedef struct { int a; } s_t;   

int open_device(s_t **dev, int index); 

int main(void){ 
        s_t *device = NULL;
        open_device(&device, 1);
        printf("A=%d\n", device->a);
        free(device);
}

int open_device(s_t **dev, int index){
        *dev = (s_t *)malloc(sizeof(s_t));   
        (*dev)->a = 42;
        return 1;
}

[download]

How does that translate to Perl? Hmmm again a guess:

my $serial_number = "00000001"; # from dmesg output

my $index = rtlsdr_get_index_by_serial( $serial_number ); # it returns
+ 0, this is not an error value so I think is good

my $name = rtlsdr_get_device_name( $index );
print "device name '$name'\n";

my $device = undef; # = SDL::...->new() ??? # i don't think so/how?
my $status = rtlsdr_open( \$device , $index)
print "status $status for index $index\n";

[download]

cool project!

bw, bliako

In reply to Re: help with XS pointers by bliako
in thread help with XS pointers by Bpl

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