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Identifying which Linux system library contains a function

Answer 1

A:

From the manpage (man lstat):

LSTAT(P)

NAME
       lstat - get symbolic link status

SYNOPSIS
       #include <sys/stat.h>

       int lstat(const char *restrict path, struct stat *restrict buf);

ar 2010-02-24 14:27:13

OP wants to know what library the functions eventually get stored in, not what header file.

Duck 2010-02-24 14:31:57

Answer 2

A:

This is one way to do it:

tomislav@malik:~$ cd /usr/lib
tomislav@malik:/usr/lib$ grep "lstat()" *
Binary file libperl.so.5.10 matches
Binary file libperl.so.5.10.0 matches
tomislav@malik:/usr/lib$

Tomislav Nakic-Alfirevic 2010-02-24 14:41:39

libperl? That can't be right. Use the 'nm' command instead. Such as `nm lib*.so* | grep lstat`.

Martin Wickman 2010-02-24 14:45:39

Yes, the grep shows also _imports_, I believe, thus the wrong result about libperl.

Thomas Tempelmann 2010-02-24 14:59:41

libperl matches because it contains the string `lstat()`, which is a Perl function implemented here. That has little to do with the underlying syscall.

ephemient 2010-02-25 04:07:21

Answer 3

A:

lstat is in libc, and libc is linked in by default. You don't need to do anything to use lstat besides including the header file for it #include <sys/stat.h>

man pages usually state which library they are in.

nos 2010-02-24 14:55:24

I think I clearly pointed out that this is not about C but about a dev env where I need to specify the lib explicitly.

Thomas Tempelmann 2010-02-24 14:57:09

Nevertheless, it is in libc, so link to libc. If this is is some environment that has little to do with what's normally found on a linux machine you need to tell us what kind of environment this is.There is no stock way to know where functions resides besides its documentation - which sometimes is lacking.

nos 2010-02-24 15:08:18

nos -- the only reason why I could not find it in libc was that it wasn't declared there, as you pointed out above. I've solved it now, thanks.

Thomas Tempelmann 2010-02-24 15:19:30

if you edit this reply, I can upvote you :)

Thomas Tempelmann 2010-02-24 15:20:26

Answer 4

+1 A:

Build a simple testcase in C, compile it and run 'ldd -r' on it to check what libs are loaded. If you don't get lstat() in C then you have a problem on your dev env. Or this env dates back before the age of symlinks :-)

bernard 2010-02-24 15:10:55

Good idea.In this case the problem actually was that there is really no lstat in the lib, but only __lxstat. Which could be seen in the headers, though.

Thomas Tempelmann 2010-02-24 15:17:09

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Identifying which Linux system library contains a function

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