需要ctypes char *指针

Question

I have a C function returning strings (char *), let's call it foo() . In python I want to call it and use it's return value, and when I'm done, I want to call an other C function which frees the string foo returned.

How can I get both the pointer and the string itself? If I do like this:

fooFunc = foolib.foo
fooFunc.restype = c_char_p
r = fooFunc()

Then I get the string, but not the pointer. If I do it without specifying the restype , I get an int which seems to be the correct address, but whenever I try to cast it to sting with c_char_p(<address>) it crashes with segmentation fault.

Answer 1

I'm surprised you can't just pass back the c_char_p instance to the second function, but I don't have the tools at hand to verify why it would fail.

However, as an alternative, I believe you could try:

• Specifying the restype as a simple pointer ( c_void_p )
• When you want to manipulate the string, use ctypes.string_at to build it
• Pass the initially returned pointer to the freeing function.