Can I set a data breakpoint in runtime in System C (or in Plain Vanilla C++)?

I have a class in system-C with some data members as such:

long double x[8];

I'm initializing it in the construction like this:

for (i = 0; i < 8; ++i) {
    x[i] = 0;
}

But the first time I use it in my code I have garbage there.

Because of the way the system is built I can't connect a debugger easily. Are there any methods to set a data breakpoint in the code so that it tells me where in the code the variables were actually changed, but without hooking up a debugger?

Edit: @Prakash: Actually, this is a typo in the question, but not in my code... Thanks!

From stackoverflow Nathan Fellman

• Sure, it will be garbage!

  The code should have been as

  for (i = 0; i < 8; ++i) {
      x[i] = 0;
  }
  

  EDIT: Oops, Sorry for underestimating ;)

  From Prakash

• Just use printk/syslog.

  It's old-fashioned, but super duper easy.

  From Frank Krueger

• @Frank

  Actually, that lets me log debug prints to a file. What I'm looking for is something that will let me print something whenever a variable changes, without me explicitly looking for the variable.

  From Nathan Fellman

• How about Conditional breakpoints? You could try for various conditions like first element value is zero or non zero, etc??

  From Prakash

• That's assuming I can easily connect a debugger. The whole point is that I only have a library, but the executable that linked it in isn't readily available.

  From Nathan Fellman

• You could try starting a second thread which spins, looking for changes in the variable:

  
  #include <pthread.h>
  
  void *ThreadProc(void *arg)
  {
    volatile long double *x = (volatile long double *)arg;
    while(1)
    {
      for(int i = 0; i < 8; i++)
      {
        if(x[i] != 0)
        {
          __asm__ __volatile__ ("int 3");  // breakpoint (x86)
        }
    }
  
    return 0;  // Never reached, but placate the compiler
  }
  ...
  pthread_t threadID;
  pthread_create(&threadID, NULL, ThreadProc, &x[0]);
  

  This will raise a SIGTRAP signal to your application whenever any of the x values is not zero.

  From Adam Rosenfield