UNIX for Dummies Questions & Answers

Hi,
I am studying exec family of functions.Its man page says,it replaces the current process image with a new process image. If it replaces the binary,then after returning back,how does it get the previous parameters of the process which called exec?As replacing process image means replacing all its memory sections.
Thanks
Radha

A successful exec call replaces the current program with another program. We can't get back to the previous executable. If you want keep both processes, you may use vfork() and then exec().

I have some part of code like I have a loop for(index = 0; index < SOME_MAX_VAL;index++) { exec(SOME_EXECUTABLE,index); } then where the value of argument index will be stored, i.e. after returning from exec executable,how it will get index?

You don't seem to grasp a very fundamental aspect of the exec family of functions: if an invocation succeeds, it can never return, because there is nothing to return to, because what had been there has been replaced.

With that in mind, unless the intent is to blindly retry after an exec failure, your loop is absolutely pointless.

In case you are wording your question badly, the index is made available to SOME_EXECUTABLE via argv.

Regards,
Alister

Perhaps this kind of model serves your purpose.
Every time fork a child process, where it loads the executable with index as argument.
Parent process continues looping on index value.

Code:

for(index = 0; index < SOME_MAX_VAL;index++)
{
  pid = fork();
  if( pid > 0 )
    continue;
  else
    exec(SOME_EXECUTABLE,index);
}

NOTE: Please use the code tags, when you are exemplifying with code snippets.

I consider that code dangerous because, when exec fails, the child code will fall into that same loop and start making its own child processes, which will start making their own child processes -- a forkbomb. Always put an exit() after your exec()'s, just in case!

Code:

for(index = 0; index < SOME_MAX_VAL;index++)
{
  pid = fork();
  if( pid > 0 )
    continue;
  else
  {
    exec(SOME_EXECUTABLE,index);
    perror("exec failed");
    exit(1);
  }
}