我将我的应用程序嵌入到Julia中,我需要一种从Julia和C读取/写入相同结构的好方法.
在Python中我可以简单地做到:
ffi.cdef("""
struct keyboard_s {
int forward;
int backward;
int left;
int right;
int jump;
}
struct keyboard_s *app_get_keyboard();
"""
app = ffi.dlopen("app.dll")
thekeyboard = app.app_get_keyboard();
thekeyboard.forward = 1; # this would immediatly change the memory in C
但是,我在Julia和Julia中尝试这样的事情总是只是复制数据并且无法从C更改外部存储器地址:
type keyboard_s
forward::Int32
backward::Int32
left::Int32
right::Int32
jump::Int32
end
# lets imply this would return the memory struct just like app_get_keyboard()
# I just use malloc(sizeof(keyboard_s)) so everybody here can test for themselves...
address = ccall(:malloc, (Int64), (Int64, ), sizeof(keyboard_s))
# address is now a valid Int64 address, so lets map it as pointer of type keyboard_s
ptr = Ptr{keyboard_s}(address)
# thekeyboard contains now the random data from the c static memory
thekeyboard = unsafe_load(ptr)
# this will change only the value of "thekeyboard",
# it doesn't touch C the Int64 address memory pointer...
thekeyboard.forward = 123 # this has no effect on the real memory address :(
# lets load the keyboard again from same address
thekeyboard = unsafe_load(ptr)
thekeyboard.forward == 123 # this is false! no effect whatsoever in C memory from Julia
我怎么能在Julia中与C共享结构的内存地址?
最佳答案 好吧,我想出了一个很好的出路,这并不觉得太尴尬.我基本上重载[]运算符来通过符号访问struct字段,如下所示:
thekeyboard[:forward] = 123
代码:
function offsetof(type_, member::Symbol)
for (i, item) in enumerate(fieldnames(type_))
if item == member
return fieldoffset(type_, i)
end
#print(typeof(i))
end
# what to do when symbol not in type_?
throw("$type_ has no member named $member")
end
function GetStructType(type_, member::Symbol)
for (i, item) in enumerate(fieldnames(type_))
if item == member
return fieldtype(type_, i)
end
#print(typeof(i))
end
# what to do when symbol not in type_?
throw("$type_ has no member named $member")
end
function Base.getindex(ptr::Ptr{T}, s::Symbol) where {T}
address = UInt(ptr)
if address == 0
throw("Base.getindex(Ptr::{$T}) would dereference a NULL pointer")
end
offset = offsetof(T, s)
fieldtype = GetStructType(T, s)
fieldptr = Ptr{fieldtype}(address + offset)
#log("Symbol $s $ptrtype address=$address offset=$offset fieldtype=$fieldtype ptr=$ptr fieldptr=$fieldptr\n")
#return 123
return unsafe_load(fieldptr)
end
function Base.setindex!(ptr::Ptr{T}, value, s::Symbol) where {T}
address = UInt(ptr)
if address == 0
throw("Base.setindex!(Ptr) would write to a NULL pointer")
end
offset = offsetof(T, s)
fieldtype = GetStructType(T, s)
fieldptr = Ptr{fieldtype}(address + offset)
#log("Symbol $s $ptrtype address=$address offset=$offset fieldtype=$fieldtype ptr=$ptr fieldptr=$fieldptr\n")
unsafe_store!(fieldptr, value)
return value
end