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How is the compilation and use of the unix platform dynamic link library, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain in detail for you, people with this need can come to learn, hope you can get something.

Under the unix platform, there are two ways to use DLL, link and dlopen. You need to set LD_LIBRARY_PATH as the lookup path (earlier versions of AIX use LIBPATH). The link method loads all dynamic libraries connected at compile time when the program starts, and does not close until the end of the program. The dlopen way is to load the dynamic library as specified by the parameters during the run, and you can use the dlclose function to turn it off until the next time you use dlopen to reload. Therefore, the link method cannot update the dynamic library version without restarting the application, but the dlopen method can.

The compilation parameters of dynamic link libraries for each platform are as follows. File wel.c, compiled into libwel.so (HPUX is libwel.sl).

# include

Void welcome (void)

{

Puts ("welcome,baby!")

}

Linux:

Compile libwel.so:

Gcc-fPIC-shared-o libwel.so wel.c-lc

-fPIC is located with a relative address

-shared generates dynamic link library

Sco unix open server:

Compile libwel.so:

Cc-K PIC-G-o libwel.so wel.c-lc

-K PIC is located with a relative address

-G generates a dynamic link library with the-b elf option

AIX:

Compile libwel.so:

Xlc-G-bnoentry-o libwel.so wel.c-lc

-G specifies to generate a dynamic link library

-bnoentry dynamic library does not require module entry (this parameter is required for lower versions of AIX)

HP UX:

Compile libwel.so:

Cc + z-c wel.c

Ld-b-o libwel.sl wel.o-lc

+ z is located with a relative address

-b generate dynamic link library

SUN OS: similar to SCO,man, the help is not comprehensive

Compile libwel.so:

Cc-G-o libwel.so wel.c-lc

-G generates dynamic link library

The compilation parameters for using dynamic link libraries in link mode are as follows. File welcome.c, compiled into a welcome executable program.

Extern void welcome (void)

Int main (void)

{

Welcome ()

Return 0

}

Linux:

Gcc-rdynamic-o welcome welcome.c-L. -lwel

-rdynamic exports all symbols for dynamic use

Sco unix open server:

Cc-b elf-o welcome welcome.c-L. -lwel

-b elf must use ELF's executable file format

AIX:

Xlc-bdynamic-brtl-o welcome welcome.c-L. -lwel

-bdynamic uses dynamic connection, which is the default of the system

The-brtl-l parameter uses .so as the library

HP UX:

Cc-dynamic-o welcome welcome.c-L. -lwel

-dynamic uses dynamic connection, which is the default of the system

SUN OS:

Compile libwel.so:

Cc-B dynamic-o welcome welcome.c-L. -lwel

-B dynamic uses dynamic connection

Dlopen mode, in fact, is to open the dynamic library and find the symbol of the action in the program to execute. So the compiled executable is the same as the normal one, as long as you connect to the libdl.so library. File welcome.c, compiled into a welcome executable program.

# include

Int main (void)

{

Void * handle

Void (* welcome) (void)

Handle=dlopen ("libwel.so", RTLD_LAZY)

Welcome=dlsym (handle, "welcome")

(* welcome) ()

Return 0

}

Linux:

Gcc-rdynamic-o welcome welcome.c-ldl

-rdynamic exports all symbols for dynamic use

-ldl uses system libdl.so libraries dlopen (), dlsym (), dlerror (), dlclose ()

Sco unix open server:

Cc-b elf-o welcome welcome.c-lc

-b elf in elf format, dynamic link libraries must

AIX:

Xlc-bexpall-o welcome welcome.c-ldl-lc

-bexpall enables the symbols of the main program to be used by passive libraries

HP UX:

Cc-o welcome welcome.c-ldl-lc

SUN OS:

Cc-o welcome welcome.c-ldl-lc

When AIX runs the dynamic library, the unified management of system memory is loaded, so that even if the program has exited, it is still thought to be in use at compile time and cannot be overwritten. There are two ways, one is for root users to execute slibclean to clean up dynamic libraries that the system loads but no one uses, and the other is to compile the library chmod go-rwx, which makes groups and others have no permissions, which the library system considers user-specific and does not load.

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