Question

Before the actual implementation, i wrote a small prototype code, and put a class constructor and ctor constructor in the same file, to see if the ctor would execute first, which is my actual implementation.

However, i am facing an error. Here is the code:

#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <iostream>

using namespace std;

extern "C" void startMe(void) __attribute__ ((constructor(1)));
extern "C" void ending(void) __attribute__ ((destructor));

class Test {

 public:

    Test()
    {
      cout << "This is test constructor" << endl;
    }
 };

 int main()
 {
  Test();
  printf("Now main called\n");
 }

 void startMe(void)
 {
  printf("Start me called before main\n");
 }

 void ending(void)
 {
  printf("Destructor called\n");
 }

—

Output:
 $ g++ constructor1.cc 
 constructor1.cc:10: error: wrong number of arguments specified for ‘constructor’ attribute

However, when i remove the constructor priority, it compiles and runs fine. That is, i do:

extern "C" void startMe(void) __attribute__ ((constructor)); 

Why is it so? How to give priority?

Please help me. My idea is “ctor” should be executed first, then the other (Test) constructor. The same reason, i have put ctor as a priority 1.

Answer 1

Compiling your program as is yields:

warning: constructor priorities from 0 to 100 are reserved for the implementation

Changing the priority from 1 to 101 gets rid of the warning and the executable produces:

 Start me called before main
 This is test constructor
 Now main called
 Destructor called

This is using GCC 4.5