python ctypes cast get null string

Question

b is address

if b_v.value is a common character, this is normal. But if b's content is hex like "1122001314" Long as it contains hex "00" the result maybe is 1122 the 001314 should be lose

Now I want get all content "1122001314". Please give me some method thanks.

the code is:

b_v=ctypes.cast(b,ctypes.POINTER(ctypes.c_char_p))

print binascii.b2a_hex(b_v.value)

example:

import ctypes
import binascii

va=binascii.a2b_hex('1212273031003535')
tt=ctypes.create_string_buffer(va)
b=ctypes.addressof(tt)
b_v=ctypes.cast(b,ctypes.c_char_p)
print binascii.b2a_hex(b_v.value)

now the result is :"1212273031"

i want the result is "1212273031003535"

Weclome to Stackoverflow. Please try to improve the wording on your question, or give a concrete code-example that illustrates what you want (input and expected output). It is very hard to understand your question. — Björn Pollex
– Björn Pollex, Commented Aug 23, 2012 at 7:03

MostafaR · Accepted Answer · 2012-08-23 08:33:35Z

2

In the line tt=ctypes.create_string_buffer(va) You are building a string_buffer from a hexadecimal representation of data (binary data) and It's wrong, because c string terminates with first 0-value character. So your data breaks. Fortunately ctypes serves raw-data in addition to string value, so with tt.raw you can access your original data and you can use binascii.b2a_hex(tt.raw), but I'm not sure It's useful for you or not.

If you want to run b=ctypes.addressof(tt) and pass the address to somewhere else and then retrieve data from address by b_v=ctypes.cast(b,ctypes.c_char_p), I should say It's not possible with string_buffer type because your data is not text, It's a binary data and you can't store it in a string_buffer and then access to it with It's address.

You can retrieve data with knowing b if you know length of data too, Try this:

b, l = ctypes.addressof(tt), len(tt) - 1 # l - 1, because there is one extra byte for terminator NULL

#Somewhere else:
b_v=ctypes.cast(b, ctypes.POINTER(ctypes.c_char * l))
print binascii.b2a_hex(b_v.contents)

edited Aug 23, 2012 at 8:33

answered Aug 23, 2012 at 7:25

MostafaR

3,7051 gold badge20 silver badges24 bronze badges

Sign up to request clarification or add additional context in comments.

9 Comments

w32c Over a year ago

binascii.b2a_hex(tt.raw) is useful but Only through b get content

w32c Over a year ago

b_v=ctypes.cast(b,ctypes.c_char_p) and this line can be changed

MostafaR Over a year ago

You can retrieve data using b, If and only if you know length of data, I had added an example to my answer

w32c Over a year ago

very very very thanks MostafaR thanks your method is usefull i love you ^_^

jfs Over a year ago

you could also try: type(tt).from_address(b) though it leaves terminating NUL in the data

|

Collectives™ on Stack Overflow

python ctypes cast get null string

1 Answer 1

9 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

9 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related