Re: ld --wrap and zcat

[Shaun Jackman <sjackman@bcgsc.ca>]

Neat, I didn't think of that. Thanks, Nick.

The solution I settled didn't require LD_PRELOAD, which I'm happy 
about, but did use -ldl and dlsym. I created a function `fopen' in my 
application, which -- and I don't entirely understand why this is -- 
libstdc++ does call. Within my fopen, I used dlsym(RTLD_NEXT, "fopen") 
to call the fopen of libc.

Cheers,
Shaun

Nick Clifton wrote:
> Hi Shaun,
> 
>> fstream::open in libstdc++ calls fopen in libc. I'd like to use ld 
>> --wrap to hook the fopen call to call popen to decompress a .gz file 
>> using zcat. Is this possible with ld --wrap? From my experimentation, it 
>> seems not. Is this possible using LD_PRELOAD and dlsym?
> 
> Do you have access to the linker command line used to build your 
> executable ?  If so you can just create your own custom library that 
> contains its own implementation of fopen (which calls popen as you 
> desire) and then insert the name of this library in between the 
> libstdc++-v3 library and the libc library on the linker command line.
> 
> Cheers
>    Nick