Re: wrapping C functions
- Posted by ghaberek (admin) Feb 22, 2013
- 1456 views
That's a little risky, you don't know if the integer might actually need to be a double. You should go through the format string instead and determine the types that way.
Agreed. I guess I should have pointed that out. My method is really more applicable to functions that take a variable number of the same type, typically pointers to objects. In any case, I would rely on the programmer to make the correct usage and adapt my method as necessary.
Parsing the format string would certainly work, but would also require much more code for a very small gain (one often knows what one is feeding a printf function). Perhaps we could pass the sequence of types directly...
procedure euSerialPrintf(integer fd, sequence fmt, object args = {}, object types = {}) if atom( args ) then args = {args} end if if atom( types ) then types = {types} end if if length( args ) != length( types ) then crash( "euSerialPrintf: args and types must be the same length! %d != %d\n", {length(args),length(types)} ) end if integer serialPrintf = link_c_proc(dll_ptr, "serialPrintf", {C_INT, C_POINTER} & types) -- ...perform caching here... c_proc(serialPrintf, {fd, allocate_string(fmt,1)} & args) end procedure
I was thinking that too. Then it dawned on me, there is a far simpler way:
serialPrintf = link_c_proc(dll_ptr, "serialPrintf", {C_INT, C_POINTER}) procedure euSerialPrintf(integer fd, sequence fmt, object args) c_proc(serialPrintf, {fd, allocate_string(sprintf(fmt,args),1)}) end procedure
While this method certainly works, it is only applicable in this situations. Other variadic functions may not be so convenient. 
-Greg
