将C ++转换为python-memcpy uchar转换为int64

Question

Alright, I'm copying some code (C++) that needs to run on my server (Python), everything was going well until the bit below.

In a nutshell here is what I have in the C++ program:

 int main() {
 ...
 ...
 int64 value = 0;
 bool blah = function1(&value);
 ...
 }

 bool function1(int64* value)
 {
 ...
 uchar pb[8];
 pb = '\x00\x00\x00\x00*Q \x00'; 
 memcpy(value,pb,8);
 //now value has the value '0x7fff33516970'
 }

So yeah, it creates some char array and then copies the value into an int64.

Now my question is: how do I do that in Python? I mean, I have the bytestring that is equivalent to pb but I have no idea where to go from there (especially since there are all those zeroes...)

Answer 1

Take a look at struct module, especially at struct.unpack . You can do:

value, = unpack("q", string)

"q" means 64-bit signed integer and string is simply a raw byte representation of the number. And remember, watch out the endianness!

Answer 2

Single quotes are used for characters, not strings in C++. Should be "\\x00\\x00\\x00\\x00*Q \\x00" . Besides, the code makes little sense in that memory is allocated for pb and then it's overwritten with a constant string.