Adding LUA tutorials: lua_calls_C1 - lua_calls_C5

Adding blinker demo: lua_blink_led

lua/examples/lua_calls_C3/Makefile

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+CC       = mipsel-openwrt-linux-gcc
+CXX      =  mipsel-openwrt-linux-g++
+OPENWRT_BUILD_DIR = /home/cain/Embedded/ingenic/sakc/build/openwrt-xburst/staging_dir/target-mipsel_uClibc-0.9.30.1
+INCLUDE  = -I. -I$(OPENWRT_BUILD_DIR)/usr/include/
+WARNINGS = -Wcast-align -Wpacked -Wpadded -Wall 
+CCFLAGS  = ${INCLUDE} ${DEBUG} ${WARNINGS} -std=c99 -fPIC
+LDFLAGS  =
+DEBUG    = -O3 -g0
+NANO_PATH = root@192.168.254.101:
+TARGET   = candy
+
+$(TARGET): $(TARGET)
+	$(CC)  $(CCFLAGS) -o $(TARGET).so -shared $(TARGET).c
+
+.c.o:
+	$(CC) -c $(CCFLAGS) -o $@
+
+upload: $(TARGET)
+	scp $(TARGET).so top3.lua $(NANO_PATH)
+
+
+clean:
+	rm -f *.o $(TARGET).so

lua/examples/lua_calls_C3/README

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+Examples from http://www.wellho.net/mouth/1844_Calling-functions-in-C-from-your-Lua-script-a-first-HowTo.html
+
+If you may with to pass a table from your Lua script into a C function, so that the C function can make use of a value from the table code like this:
+
+    stuff = {hotel = 48, hq = 404, town = 1}
+    ....
+    summat = extratasks.dothis(stuff)
+
+This isn't as easy as just passing a value, since the size of a table can vary, and Lua's dynamic memory allocation doesn't sit well, in a simple interface, with C's static model. The "trick" is to tackle it within the C code by using function calls to get (and if necessary) reset values from the table - with the data required by those function calls being processed via the Lua stack.
+
+    /* Looking up based on the key */
+    /* Add key we're interested in to the stack*/
+    lua_pushstring(L,"hq");
+    /* Have Lua functions look up the keyed value */
+    lua_gettable(L, -2 );
+    /* Extract the result which is on the stack */
+    double workon = lua_tonumber(L,-1);
+    /* Tidy up the stack - get rid of the extra we added*/
+    lua_pop(L,1);
+
+That code retrieves the "hq" value from the table that's been passed in (called stuff in my Lua example above) and stores it into a C variable called workon ... objective achieved!
+

lua/examples/lua_calls_C3/candy.c

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+
+/* This is the third (of three) examples of calling from
+a Lua script to a C library.  In this example, we have
+registered multiple C functions with the Lua, and we have
+also passed in a table which is intrinically much harder
+to handle as it doesn't map directly to a C type. */
+
+#include "lua.h"
+#include "lauxlib.h"
+#include <stdio.h>
+
+/* The peardrop function is called with a single
+numeric  parameter, and it returns a number */
+
+static int peardrop ( lua_State *L) {
+        printf ("lua SIE's test\n");
+        double trouble = lua_tonumber(L, 1);
+        lua_pushnumber(L, 16.0 - trouble);
+        return 1;
+        }
+
+/* The humbug function is called with a TABLE as
+its parameter (or it should be!).  It extracts the
+element with the key "hq", and returns 123 more
+than that number (the sum added is just done to
+demonstrate the C doing something! */
+
+static int humbug ( lua_State *L) {
+        printf ("Enter humbug function\n");
+
+        /* Is it a table? */
+        if (lua_istable(L,-1)) {
+                printf("Table passed to humbug\n");
+
+                /* Looking up based on the key */
+                /* Add key we're interested in to the stack*/
+                lua_pushstring(L,"hq");
+                /* Have Lua functions look up the keyed value */
+                lua_gettable(L, -2 );
+                /* Extract the result which is on the stack */
+                double workon = lua_tonumber(L,-1);
+                /* Tidy up the stack - get rid of the extra we added*/
+                lua_pop(L,1);
+
+                /* We can now use the result */
+                lua_pushnumber(L, workon + 123.0 );
+        } else {
+                printf("Not a Table passed to humbug\n");
+                lua_pushnumber(L, 12.0 );
+        }
+        return 1;
+        }
+
+/* This registers "dothis" and "dothat" with Lua, so that when
+they're called they run the humbug and peardrop functions respectively */
+
+int luaopen_candy ( lua_State *L) {
+        static const luaL_reg Map [] = {
+                {"dothis", humbug},
+                {"dothat", peardrop},
+                {NULL,NULL}
+                } ;
+        /* dothis and dothat are put in the extratasks table */
+        luaL_register(L, "extratasks", Map);
+        return 1;
+        }
+         

lua/examples/lua_calls_C3/top3.lua

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+
+--[[ This is a short (demonstration) piece of Lua
+script which calls in some C functions from a file
+called candy.c;   the functions are accessed via a
+table called extratasks (that's defines in the
+C code) and called via the names dothis and dothat -
+again defined in the candy.c file
+]]
+
+-- Setting up demo variables that will be passed to C
+print("Lua code running ...")
+stuff = {hotel = 48, hq = 404, town = 1}
+
+-- Loading and calling the C
+require "candy"
+summat = extratasks.dothis(stuff)
+somemore = extratasks.dothat(summat)
+
+-- Lua code to show you the results
+print ("... back into Lua code")
+print ("Values in Lua now", summat, somemore)
+print ("Table contains ...")
+for k,v in pairs(stuff) do
+        print (k,v)
+        end