static or shared

static or shared

[Mohammed Khalid Ansari]

Hi,

If /usr/lib contains both static and shared libraries of the same name 
eg odbc, which library compiler is going to take if I do..

gcc file.c -lodbc

How do I explicitly I define which library to take during compilation.

-- 

**************************************************************************

Mohammed Khalid Ansari                    Tel (res) : 0091-022-3051360
Assistant Manager II                          (off) : 0091-022-2024641
National Centre for Software Technology   Fax       : 0091-022-2049573 
8th flr,Air India Build. Nariman Point,   E-Mail    : khalid@ncst.ernet.in 	
Mumbai 400021.

Homepage : http://soochak.ncst.ernet.in/~khalid			  	  

**************************************************************************

Re: static or shared

[Jan-Benedict Glaw]

[-- Attachment #1: Type: text/plain, Size: 956 bytes --]

On Tue, 2003-01-07 16:49:29 +0530, Mohammed Khalid Ansari <khalid@ncst.ernet.in>
wrote in message <Pine.LNX.4.33.0301071646230.5493-100000@soochak.ncst.ernet.in>:
> 
> Hi,
> 
> If /usr/lib contains both static and shared libraries of the same name 
> eg odbc, which library compiler is going to take if I do..
> 
> gcc file.c -lodbc
> 
> How do I explicitly I define which library to take during compilation.

"-l" is commonly used for shared libraries. If you want to statically
link some library into your program, simply name it's file name as one
of the object file names which are to be linked. But beware! Libs need
to be on the end of your file list.

MfG, JBG

-- 
   Jan-Benedict Glaw       jbglaw@lug-owl.de    . +49-172-7608481
   "Eine Freie Meinung in  einem Freien Kopf    | Gegen Zensur
    fuer einen Freien Staat voll Freier Bürger" | im Internet!
   Shell Script APT-Proxy: http://lug-owl.de/~jbglaw/software/ap2/

[-- Attachment #2: Type: application/pgp-signature, Size: 189 bytes --]

Re: static or shared

[Glynn Clements]

Mohammed Khalid Ansari wrote:

> If /usr/lib contains both static and shared libraries of the same name 
> eg odbc, which library compiler is going to take if I do..
> 
> gcc file.c -lodbc

Shared libraries are preferred over static libraries, unless you use
the -static flag (in which case, only static libraries are used).

> How do I explicitly I define which library to take during compilation.

You can specify an explicit filename, e.g. /usr/lib/libodbc.a
(however, you shouldn't do this for shared libraries).

IIRC, you can also use e.g.

	gcc ... -Wl,-Bstatic -lodbc -Wl,-Bdynamic ...

to link specific libraries statically.

-- 
Glynn Clements <glynn.clements@virgin.net>

strange segmentation fault in malloc()

[qhwang]

Hi, there!

My app wants to read and then wavelet-transform image one by one. Now I got
a strange segmentation fault in malloc().  The situation is only the first
image can be processed successfully, but the second one fails due to the
same call of "malloc(160*120*sizeof(float))" used in the processing of the
first image. The return value of "malloc" is NULL . So how can I check the
size of heap used by the system? Or how can I set the environment varible
"MALLOC_CHECK_"? Someone said it can be set in the rc.sysinit, but I can't
find this file. Any suggestion will be greatly appreciated. Many Thanks!

qhwang

Re: strange segmentation fault in malloc()

[Glynn Clements]

qhwang wrote:

> My app wants to read and then wavelet-transform image one by one. Now I got
> a strange segmentation fault in malloc().  The situation is only the first
> image can be processed successfully, but the second one fails due to the
> same call of "malloc(160*120*sizeof(float))" used in the processing of the
> first image. The return value of "malloc" is NULL . So how can I check the
> size of heap used by the system?

In bash, "ulimit -a" will report the resource limits. However, the
malloc() function in GNU libc isn't restricted to the size of the data
segment, as it can obtain memory using "anonymous mmap()".

In any case, it's unlikely that you are really running out of memory
(160*120*sizeof(float) is only 75Kb). Unusual malloc() failures (i.e. 
failures which occur when you aren't using vast amounts of memory) are
usually caused by the heap's data structures being corrupted because
part of the code modified memory outside of the allocated block.

> Or how can I set the environment varible
> "MALLOC_CHECK_"? Someone said it can be set in the rc.sysinit, but I can't
> find this file. Any suggestion will be greatly appreciated. Many Thanks!

You can set environment variables in bash using "export", e.g.

	export MALLOC_CHECK_=1

Setting an environment variable affects all process which inherit from
the shell in which it was set.

-- 
Glynn Clements <glynn.clements@virgin.net>

Re: strange segmentation fault in malloc()

[QingHua Wang]

Thanks. I found the problem by set MALLOC_CHECK_. It's a kind of pointer
corruption in the couple of malloc/free. Thanks again.

qhwang