Haskell FFI how to take an address of the local value -

i try work simple c-code haskell:

time_t rawtime = time( null ); struct tm* timeinfo = localtime( &rawtime );  /* using address of local variable */ printf( "the current date is: %s", asctime( timeinfo ) ); 

so write:

data ctmstruct = ctmstruct type ctmstructptr = ptr ctmstruct  foreign import ccall "time"      c_time      :: ptr ctime    -> io ctime foreign import ccall "localtime" c_localtime :: ptr ctime    -> io ctmstructptr foreign import ccall "asctime"   c_asctime   :: ctmstructptr -> cstring  main :: io () main =     rawtime <- c_time nullptr     tmstructptr <- c_localtime ???  -- how address of rawtime?     print $ c_asctime tmstructptr 

so how can address of local value rawtime putting argument of c_localtime function? i've read documentation foreign module, didn't find answer question. i'd grateful help.

i able do:

import foreign.c.string import foreign.marshal.alloc  -- declarations , foreign bindings here  gettime :: io string gettime =     p <- malloc     c_time p     tmptr <- c_localtime p     str <- peekcstring $ c_asctime tmptr     free p     return str  main :: io () main =     currenttime <- gettime     putstrln currenttime 

the key using malloc , free, explicitly allocate space, pass c_time set contents, c_localtime format ctmstruct, pass c_asctime convert cstring, marshal haskell string peekcstring, , free pointer used time.

---

i guess should have realized sooner, better solution use alloca:

gettime :: io string gettime = alloca $ \p ->     c_time p     tm <- c_localtime p     peekcstring $ c_astime tm 

which safer, shorter, , easier. alloca function allocation , freeing of pointer you, have use it.