c - Use of malloc in Pthreads -

this actual c code pthreads:

threadparms *parms = null;  if ((parms = (threadparms *) malloc (sizeof (*parms))) == null)     {       goto fail0;     }    parms->tid = thread;   parms->start = start;   parms->arg = arg; 

why did choose malloc *parms instead of threadparms? looks allocating pointer (which error), apparently allocating size of whole structure. correct?

this common trick in c - using dereference pointer expression in place of actual type.

the rationale follows: if have

some_type *some_var = malloc(sizeof(*some_var)); 

and change some_type some_other_type, code continue working fine 1 change.

however, if start with

some_type *some_var = malloc(sizeof(some_type)); 

then have change some_type in 2 places:

some_other_type *some_var = malloc(sizeof(some_other_type)); 

or code have error.

it looks allocating pointer (which error)

the asterisk makes sizeof evaluate size of entire struct, code correct.