Re: [Win32] pthreads and memory allocation

[Marshall]

in reply to [Win32] pthreads and memory allocation

I am having trouble understanding even the basics of this C code.
TaskCode() returns a pointer to anything and accepts a pointer to anything.

There is nothing returned from this C subroutine,
void *TaskCode(void *argument).

tid = *((int *) argument);
means: argument is "cast" as a pointer to integer.
Then that result is de-referenced to get the "tid". A **int.

The OP's code is a memory leak because there is no pointer or other way to use the memory allocated by
"s = (char*) malloc(100);".

void *TaskCode(void *argument) 
{
   int tid;
   char * s;

   tid = *((int *) argument);
   // tid = **argument;

   printf("thread %d: calling malloc\n", tid);
   s = (char*) malloc(100);
   printf("thread %d:  malloc called\n", tid);

   return NULL;
}

"s" is a memory pointer returned by malloc(). Now a malloc() call should have a conditional statement to see that it actually worked. But the big thing here is that the subroutine TaskCode() returns bullshit. I don't see how "s", the pointer to a new memory allocation of 100 bytes can ever be used outside of TaskCode()

[syphilis]

It's just a demo to illustrate that malloc() causes a crash on Win32 (but not elsewhere, afaik).
Perhaps I should have declared char * useless_and_pointless; instead of char * s;.

Now a malloc() call should have a conditional statement to see that it actually worked

Yes, if you're wanting to make use of the memory that you've requested be allocated, I think that's a good idea. For the purposes of this demo, however, I don't really care whether the malloc succeeds or fails - I just want it to not cause a crash.
(Besides, on Win32, I'm not even going to see the result of that "conditional statement" because it never gets executed - due to afore-mentioned crash.)

Similarly, any memory leak is of no concern to me wrt this particular exercise.

Cheers,
Rob

[Marshall]

Yes,
Perhaps I should have declared char * useless_and_pointless; instead of char * s;.

Yes, I figure that would be correct and I figure that we understand each other.

The basic issue is: "s = (char*) malloc(100);". "s" is cast as a pointer to a memory address. "s" is guaranteed to point to at least 100 bytes (consecutive).