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I am trying to load the example lproc program (described on Programming Lua, Chapter 30) into Lua and fouling up somehow. I am following this - http://www.lua.org/pil/26.2.html to get my c module into lua. Following are the steps that I've taken:
I have an lproc.h and lproc.c (containing exactly the functions laid out in Chapter 30 of the book). I am compiling lproc.c as --- gcc -c lproc.c -DLUA-USERCONFIG=\"lproc.h\"
I made a library out of lproc.o, named the same.
And then compiled lua.c as instructed. My header files contain the macro LUA_EXTRALIBS and the method declarations.
Went to the Lua interpreter and it gave the following errors:
> require "lproc"
stdin:1: module 'lproc' not found:
no field package.preload['lproc']
no file './lproc.lua'
no file '/opt/local/share/lua/5.1/lproc.lua'
no file '/opt/local/share/lua/5.1/lproc/init.lua'
no file '/opt/local/lib/lua/5.1/lproc.lua'
no file '/opt/local/lib/lua/5.1/lproc/init.lua'
no file './lproc.so'
no file '/opt/local/lib/lua/5.1/lproc.so'
no file '/opt/local/lib/lua/5.1/loadall.so'
stack traceback:
[C]: in function 'require'
stdin:1: in main chunk
[C]: ?
It seems that the module did not get registered, what would I need to do from Lua? Time is short and I am doing something horrendously wrong, any direction would be welcome.
Thanks,
Sayan
449
A Lua library is a chunk that defines several Lua functions and stores them in appropriate places, typically as entries in a table. A C library for Lua mimics this behavior. Besides the definition of its C functions, it must also define a special function that corresponds to the main chunk of a Lua library.
The old way of creating modules lua : module("mymodule", package. seeall) function foo() -- create it as if it's a global function print("Hello World!") end.
The header file lua. h defines the basic functions provided by Lua. That includes functions to create a new Lua environment (such as lua_open ), to invoke Lua functions (such as lua_pcall ), to read and write global variables in the Lua environment, to register new functions to be called by Lua, and so on.
Lua offers a higher-level function to load and run libraries, called require . Roughly, require does the same job as dofile , but with two important differences. First, require searches for the file in a path; second, require controls whether a file has already been run to avoid duplicating the work.
Here is a complete and fully portable minimal example of building a C library for Lua (works in Lua 5.1-5.3 and LuaJIT, for any platform):
With this example.c:
#include <lua.h>
int example_hello(lua_State* L) {
lua_pushliteral(L, "Hello, world!");
return 1;
}
int luaopen_example(lua_State* L) {
lua_newtable(L);
lua_pushcfunction(L, example_hello);
lua_setfield(L, -2, "hello");
return 1;
}
Put this rockspec file in the same directory, named example-1.0-1.rockspec:
package = "example"
version = "1.0-1"
source = {
url = "." -- not online yet!
}
build = {
type = "builtin",
modules = {
example = "example.c"
}
}
Then, run luarocks make. It will build the C code with the correct flags for your platform.
Your module is now ready to use!
Lua 5.3.3 Copyright (C) 1994-2016 Lua.org, PUC-Rio
> example = require("example")
> print(example.hello())
Hello, world!
>
The easiest way is to create a shared library and load your C module dynamically. This way avoids having to rebuild the Lua interpreter. There are several examples in http://www.tecgraf.puc-rio.br/~lhf/ftp/lua/ and explanations in http://www.tecgraf.puc-rio.br/~lhf/ftp/lua/install.html and http://lua-users.org/wiki/BuildingModules
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