__attribute__ ((constructor)) and __attribute__ ((destructor))

☆ Use in Applications

__attribute__ ((constructor)) is executed before the main () function, and __attribute__ ((destructor)) executes when main () exits.

Reference: http://blog.sina.com.cn/s/blog_88b60ea001017bc9.html

☆ Use in Library

The function specified by __attribute__ ((constructor)) is called when the shared library loading, and the function specified by __attribute__ ((destructor)) is called when the shared library is unloading.

Reference: http://blog.csdn.net/linuw/article/details/6048307

☆ Use in Applications

1. TEST.c

1#include <stdio.h>2#include <stdlib.h>3 4 Static voidBefore (void) __attribute__ ((constructor));5 6 Static voidAftervoid) __attribute__ ((destructor));7 8 Static voidbefore ()9 {Tenfprintf (stderr,"In %s%d\n", __func__, __line__); One } A  - Static voidAfter () - { thefprintf (stderr,"In %s%d\n", __func__, __line__); - } -  - intMainvoid) + {         -printf"bengin\n"); +  Aprintf"end\n"); at     return 0; -}

2. Results

Ten

☆ Use in Library

1. libktest.c

1#include <stdio.h>2__attribute__ ((constructor))Static voidKtest_init (void);3__attribute__ ((destructor))Static voidKtest_deinit (void);4 5 voidKtest_init (void)6 {7printf"Call ktest init.\n");8 }9 Ten voidKtest_deinit (void) One { Aprintf"Call ktest deinit.\n"); - } -  the voidtest1 () - { -printf"Call test1.\n"); - } +  - voidtest2 () + { Aprintf"Call test2.\n"); at } -  - voidtest3 () - { -printf"Call test3.\n"); -}

2. calllibc.c

1#include <stdlib.h>2#include <stdio.h>3#include <dlfcn.h>/*Dlopen, Dlsym, Dlclose*/4 5 intMainintargcChar**argv)6 {7 8     /*below for testing dynamic linking loader*/9     void*handle;Ten     void(*test) (); One     Char*error; A  -printf"++++load before++++\n"); -Handle = Dlopen ("./libktest.so", rtld_lazy); the     if(!handle) { - fputs (Dlerror (), stderr); -Exit1); -     } +  -Test = Dlsym (handle,"test2"); +     if(Error = Dlerror ())! =NULL) { A fputs (Error, stderr); atExit1); -     } -  -(*test) (); -  -printf"++++unload before++++\n"); in Dlclose (handle); -  to     return 0; +}

3. TEST_CALLLIBC.C:

1#include <stdlib.h>2#include <stdio.h>3#include <dlfcn.h>/*Dlopen, Dlsym, Dlclose*/4 5 intMainintargcChar**argv)6 {7printf"++++main start++++\n");8 9     voidtest1 ();Ten     voidtest2 (); One     voidtest3 (); A  - test1 (); - test2 (); the test3 (); -printf"++++main end++++\n"); -  -     return 0; +}

4. Results

Calllibc.c

++++load before++++

Call Ktest init.
Call Test2.
++++unload before++++
Call Ktest Deinit.

Test_calllibc.c

Call Ktest init.
++++main start++++
Call Test1.
Call Test2.
Call Test3.
++++main end++++
Call Ktest Deinit.

5. Analysis

Dlopen load Dynamic Library, dclose unload dynamic Library

The compile mode, main starts before loading, and main ends after unloading.

__attribute__ ((constructor)) and __attribute__ ((destructor))