What's the difference between Py_ssize_t and size_t?

Question

When to use which one?

Answer 1

Hi Faheem
I assume you are trying to do some C coding in Python, correct?
Well, Py_ssize_t is a signed integer defined in the implementation of CPython, when indexing Python arrays in C you can can use it, see: https://stackoverflow.com/questions/20987390/cython-why-when-is-it-preferable-to-use-py-ssize-t-for-indexing

size_t is a native C type. It is a unsigned int and it has the size in bytes of the machine work. So, in 64 bits machines it will have 8 bytes size. It is also often used when indexing arrays, etc.

So, the main differences are:
1. Py_ssize_t is signed while size_t is unsigned.
2. size_t is native to C, Py_ssize_t is defined externally by a library.

Answer 2

Hi Faheem
Exactly, if you need an unsigned int, use size_t.

Answer 3

Mark Thanks!

Answer 4

Mark if I want to use unsigned variable to index the array then should I use size_t instead of Py_ssize_t?