How to compile a dynamic link library with gcc *.so file dynamic Library

Go: How to compile. So dynamic library Q: I source files for main.c, x.c, y.c, z.c, header file for x.h,y.h,z.h
How to compile into. So dynamic library.
Compilers with GCC
We'd better give you a detailed explanation of the parameters.

For:
# claims to move the connection library, assuming the name is libtest.so
GCC x.c y.c z.c-fpic-shared-o libtest.so

# Connect MAIN.C and Dynamic connection libraries to build an executable file
GCC main.c-l.-ltest-o Main

# Output LD_LIBRARY_PATH environment variable, one side dynamic library loader can find the required dynamic library
Export ld_library_path= $LD _library_path:.

# test whether the dynamic connection, if listed libtest.so, then should be connected to the normal
LDD Main

# It's not going to be done.

-fpic: For code that is compiled as location independent, the compiled code is location-dependent without this option, so dynamic loading is a way to copy the code to meet the needs of different processes, but not the purpose of real code segment sharing.

-L.: Indicates the library to connect to in the current directory

-ltest: When the compiler looks for a dynamic connection library, there is an implied naming rule, that is, precede the given name with Lib, followed by. So to determine the name of the library

Ld_library_path: This environment variable indicates that the dynamic connector can load the path of the dynamic library.
Of course, if you have root permissions, you can modify the/etc/ld.so.conf file, and then call
/sbin/ldconfig to achieve the same goal, but if you do not have root permissions, then you can only use the output Ld_library_path method.

Example:
Compilation and use of dynamic link library *.so--


Dynamic library *.so is often encountered when programming in C and C + + under Linux. Recently found a few articles in the Web site to introduce dynamic library compilation and links, finally understand this has not been very understanding of dongdong, here to make a note, but also for the dynamic Library link library and distressed brothers to provide a little help.
1, the compilation of dynamic library

The following is an example of how to generate a dynamic library. Here is a header file: So_test.h, three. c Files: test_a.c, TEST_B.C, TEST_C.C, we compile these several files into a dynamic library: libtest.so.

So_test.h:



#include <stdio.h>

#include <stdlib.h>



void Test_a ();

void Test_b ();

void Test_c ();



TEST_A.C:



#include "So_test.h"



void Test_a ()

{

printf ("This is in test_a...\n");

}



TEST_B.C:



#include "So_test.h"



void Test_b ()

{

printf ("This is in test_b...\n");

}



TEST_A.C:



#include "So_test.h"



void Test_c ()

{

printf ("This is in test_c...\n");

}



Compile these several files into a dynamic library: libtest.so



$ gcc test_a.c test_b.c test_c.c-fpic-shared-o libtest.so


2, Dynamic library links

In 1, we have successfully generated our own dynamic link library libtest.so, we use a program to invoke the function in this library. The source file for the program is: test.c.

TEST.C:



#include "So_test.h"



int main ()

{

Test_a ();

Test_b ();

Test_c ();



return 0;

}



L deliver the test.c and dynamic library libtest.so chain into the execution file test:



$ gcc test.c-l.-ltest-o Test



L test whether the dynamic connection, if listed libtest.so, then should be connected to the normal



$ LDD Test



L Execute test to see how it calls a function in a dynamic library.
3, compile parameter analysis
The main thing is an option for the GCC command line:
-shared This option specifies that a dynamic connection library is generated (which allows the connector to generate an export symbol table of type T, and sometimes a weakly connected W-type export symbol) without which the external program cannot connect. Equivalent to an executable file

L-fpic: For code that is compiled as location independent, the compiled code is location-dependent without this option, so dynamic loading is a way to copy the code to meet the needs of different processes, but not the purpose of real code segment sharing.

L-l.: Indicates the library to connect to in the current directory

L-ltest: When the compiler looks for a dynamic connection library, there is an implied naming rule, that is, precede the given name with Lib, followed by. So to determine the name of the library

L Ld_library_path: This environment variable indicates that the dynamic connector can load the path of the dynamic library.

L Of course, if you have root permissions, you can modify the/etc/ld.so.conf file, and then call/sbin/ldconfig to achieve the same purpose, but if you do not have root permissions, then only the output Ld_library_path method.
4. Note

When you call a dynamic library, there are a few problems that are often encountered, sometimes, it is clear that the library's header file directory through the "-I" included, the library file is guided by the "-L" parameter, and specified the "-L" library name, but through the LDD command to see if you can not find the link you specify the so file , all you have to do is modify the Ld_library_path or/etc/ld.so.conf file to specify the directory of the Dynamic library. This is usually done to solve the problem that the library cannot be linked.