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const char *lua_pushfstring (lua_State *L, const char *fmt, ...);
[-0, +1, m]

no need for custom allocation here ...


-----Original Message-----
From: [] On Behalf Of Marc Balmer
Sent: Monday, May 09, 2016 9:37 AM
To: Lua mailing list
Subject: How far should one go preventing potential memory leaks?

I would like to open a discussion on best practices for preventing memory leaks in C programs using the Lua API.

Consider the following code snippet:

char *s = malloc(32);
snprintf(s, 32, "bumblebee");
lua_pushstring(L, s);

lua_pushstring() could raise an error (e.g. under memory pressure) and then the subsequent free(s) would not be called, leaking the memory.

One could use lua_newuserdata() instead of malloc, but this works only if the memory is allocated by our own code, it does not work where the memory is allocated e.g. by a third party library.

So a possible way could be to create a metatable containing a __gc method, then allocating a small userdata value containging only a pointer to the allocated data. The __gc method could then free the memory, even if lua_pushstring() fails.

Is it worth the effort?  How do others (you) handle this kind of possible errors?

My personal take on this is, btw:  I don't care as I long as I don't reference NULL pointers.  If we are under memory pressure and functions like lua_pushstring() are starting to fail, we will be in much deeper trouble anyway soon... ymmv, opinions very welcome.

- mb