How do I read a C char array into a python bytearray with cython?

问题

I have an array with bytes and its size:

cdef char *bp
cdef size_t size

How do I read the array into a Python bytearray (or another appropriate structure that can easily be pickled)?

回答1:

Three reasonably straightforward ways to do it:

Use the appropriate C API function as I suggested in the comments:
```
 from cpython.bytes cimport PyBytes_FromStringAndSize

 output = PyBytes_FromStringAndSize(bp,size)
```
This makes a copy, which may be an issue with a sufficiently large string. For Python 2 the functions are similarly named but with PyString rather than PyBytes.
View the char pointer with a typed memoryview, get a numpy array from that:
```
cdef char[::1] mview = <char[:size:1]>(bp)
output = np.asarray(mview)
```
This shouldn't make a copy, so could be more efficient if large.
Do the copy manually:
```
 output = bytearray(size)
 for i in range(size):
     output[i] = bp[i]
```
(this could be somewhat accelerated with Cython if needed)

This issue I think you're having with ctypes (based on the subsequent question you linked to in the comments) is that you cannot pass C pointer to the ctypes Python interface. If you try to pass a char* to a Python function Cython will try to convert it to a string. This fails because it stops at the first 0 element (hence you need size). Therefore you aren't passing ctypes a char*, you're passing it a nonsense Python string.

来源：https://stackoverflow.com/questions/50228544/how-do-i-read-a-c-char-array-into-a-python-bytearray-with-cython

标签

cython