Magnus Österlund

I have searched in all exported header files. I can find exported functions to deallocate arrays of different types, but not strings.

I want to call LabVIEW functions from a python script and trying to understand the memory handling of strings and arrays. Let's say that I have a COM API created by LabVIEW with a function that look like this: void Foo(LStrHandle *str) I want to call this from python and use the library ctypes. I give below the code I have written so far: from ctypes import* mydll = cdll.LoadLibrary("MyDll.dll") # A typedef for the signature of a LStrHandle LVString = POINTER(POINTER(c_int)) # Cast a LStrHandle to a python string. # LStrHandle is a int32 that tell the number of chars that following # direct after the int32 in memory. def CastLVString(lvValue): if lvValue and lvValue.contents and lvValue.contents.contents: # Get the pointer from the pointer to pointer. lstr = lvValue.contents.contents # Get the value from the pointer that is the count. cnt = lstr.value if cnt > 0: # Get the bytes after cnt. Number of bytes is defined by cnt. str_bytes = cast(addressof(lstr) + sizeof(c_int32), POINTER(c_char * cnt)) # Cast the bytes to a string. return str_bytes.contents.value.decode('utf-8') return "" # Wrapper function for COM function Foo. def Foo(): mydll.Foo.argtypes = [ POINTER(LVString) ] str = LVString() mydll.Foo(byref(str)) # Cast the LStrHandle to a python string and return. return CastLVString(message) This works, but I wonder if it is correct. Aren't there better ways to handle strings (and vectors)? I wonder how the memory management works. I guess I have to tell LabVIEW that it can free the memory after I read the data. If so, how do I do it? I have seen that the function DSDisposePtr should be used if doing it from C, can this function be used in python? By the way, the C signature for LStrHandler is as following: /** @brief Long Pascal-style string types. */ typedef struct { int32 cnt; /* number of bytes that follow */ uChar str[1]; /* cnt bytes */ } LStr, *LStrPtr, **LStrHandle;