Write two functions in C using GCC compiler, one of which executes before main function and other executes after the main function.
GCC specific syntaxes :
1. __attribute__((constructor)) syntax : This particular GCC syntax, when used with a function, executes the same function at the startup of the program, i.e before main() function.
2. __attribute__((destructor)) syntax : This particular GCC syntax, when used with a function, executes the same function just before the program terminates through _exit, i.e after main() function.
The way constructors and destructors work is that the shared object file contains special sections (.ctors and .dtors on ELF) which contain references to the functions marked with the constructor and destructor attributes, respectively. When the library is loaded/unloaded, the dynamic loader program checks whether such sections exist, and if so, calls the functions referenced therein.
Few points regarding these are worth noting :
1. __attribute__((constructor)) runs when a shared library is loaded, typically during program startup.
2. __attribute__((destructor)) runs when the shared library is unloaded, typically at program exit.
3. The two parentheses are presumably to distinguish them from function calls.
4. __attribute__ is a GCC specific syntax;not a function or a macro.
Driver code :
I am called first I am in main I am called last
This article is contributed by Rishav Raj. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to firstname.lastname@example.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
- return statement in C/C++ with Examples
- size of char datatype and char array in C
- Logical Not ! operator in C with Examples
- How to implement our own Vector Class in C++?
- Web Programming in C++
- C++ Program to print an Array using Recursion
- Storage Classes in C++ with Examples
- fill_n() function in C++ STL with examples
- fill() function in C++ STL with examples
- How to erase an element from a vector using erase() and reverse_iterator?
- iomanip setbase() function in C++ with Examples
- iomanip setpricision() function in C++ with Examples
- iomanip setiosflags() function in C++ with Examples
- iomanip setfill() function in C++ with Examples