gethostbyname, getprotobyname, getservbyname...

Wszebor · 11-11-2004, 04:42 PM

Functions "getprotobyname()", "getservbyname()" and other similar are returning a pointer to a structure. But who allocates the memory for these? I suppose it is done by these functions. Question is: have I to free returned pointers?

If these functions allocate memory for these structures then after some hundreds of calls i'll have no memory?

Perhaps there is a one static place for these structures and when I call functions next time, the same place for structure is used (this overwrites old data in structure?).

Please help me.

itsme86 · 11-11-2004, 06:57 PM

According to man gethostbyname:

Quote:

The functions gethostbyname() and gethostbyaddr() may
return pointers to static data, which may be overwritten
by later calls. Copying the struct hostent does not suf_
fice, since it contains pointers - a deep copy is
required.

Which means that they don't necessarily allocate memory. They have a hostent struct declared as static which makes its value valid after the function has returned. Your assumption about overwriting previous data with subsequent calls is correct. You may also want to look at gethostbyname_r() which is a reentrant variation of it.

Wszebor · 11-12-2004, 06:04 AM

Thx - I missed this fragment in man. Now I understand.