nn-usb-fpga/lua/examples/lua_calls_C2

Examples from http://www.wellho.net/mouth/1844_Calling-functions-in-C-from-your-Lua-script-a-first-HowTo.html


The code is very similar, but you'll notice six additions - in the Lua:

a) We have added a parameter to the call to dothis in the Lua
b) We have added an assignment to collect a return value from the C

summat = cstuff.dothis(value)

c) We have printed out these values
print ("Values in Lua now",value, summat)


and in the C:

d) We have used lua_tonumber to collect a numeric value that was passed from the Lua to the C; you'll note that all such numbers are treated as doubles. The parameter "1" indicates 1 down - i.e. top of - the state stack.

  double trouble = lua_tonumber(L, 1);

e) We have performed a calculation (representative of something being done in the C code) and pushed the result of this back onto the Lua state stack so that it can be picked up once we have returned from the C to the Lua

  lua_pushnumber(L, 16.0 - trouble);

f) We have changed return 0 into return 1 to indicate that one result is being returned.

  return 1; }