Linux dynamic library search path priority

Linux dynamic library search path priority-general Linux technology-Linux programming and kernel information. For details, see the following. By Ronnie: 13761598350 E-mail: ghnghnghnghn@163.com

Generally, the default search paths for Linux dynamic libraries are/lib and/usr/lib. After a dynamic library is created, the created dynamic library is usually copied to these two directories. When running the application, the system will go to these two paths to call the dynamic library. However, in addition to the two methods to specify the search path for a dynamic library, there are two other methods: editing the configuration file and specifying the environment variables. However, these four search paths have different priorities.

We first create three files tlib. h In the directory at the same level:

# Ifndef _ TLIB _
# Define _ TLIB _

Void fun (void );

# Endif

Tlib. c:

# Include
# Include "tlib. h"

Void fun ()
{
Printf ("This is a test \ n ");
}

And test. c:

# Include
# Include "tlib. h"

Int main ()
{
Fun ();
Return 0;
}

In general, no matter which method is used to specify the search path of the dynamic library, these steps are indispensable:

① Gcc? FPIC? Wall? C tlib. c generate the. o file

② Gcc-shared-fPCI-o libtlib. so tlib. o to generate a dynamic library

③ Gcc-o test. c-L .? Ltlib generates executable files

Note that the dynamic library file name must start with lib.

The following describes the four methods one by one:

To make the test more intuitive, we can change the content printed by the fun function in tlib. c before doing each method, and then perform steps ① To ③ above.

Method 1:
Add the path of the dynamic library to the configuration file/etc/ld. so. conf. After editing, enter ldconfig in the command line.

Method 2:
Specify the environment variable export LD_LIBRARY_PATH = [path of the dynamic library].

Method 3:
Copy the dynamic library to the/usr/lib directory.

Method 4:
Copy the dynamic library to the/lib directory.

After testing, we can see that the priority of the search path in a dynamic library is from high to low: method 2, method 1, Method 4, and method 3.