ctypes types

Learn C types with c_int, c_char_p.

c_int and c_char_p

ctypes provides classes that represent C types in Python. c_int stands for C int, c_char_p for a C char* pointer.

After creating a C type you access the Python value through .value. c_int(42).value gives 42. c_char_p(b"kutu").value gives the byte string b"kutu"; you convert it to text with .decode(). These types are needed to match function arguments and return values correctly.

Other C types

ctypes provides many C types: c_double (double), c_long (long), c_size_t (size_t), c_void_p (void*).

Each type's .value attribute works for both reading and writing. a = c_int(5); a.value = 10 changes the value. The types are used as class names when defining argtypes and restype. Choosing the right type prevents data loss and crashes.

Exercise Store values with C types

Import the module with import ctypes. Create a C int with ctypes.c_int(42). Create a C string pointer with ctypes.c_char_p(b"kutu"). Print the .value of both; decode the second to text with .decode().

Show example solution

import ctypes

a = ctypes.c_int(42)
b = ctypes.c_char_p(b"kutu")
print(a.value)
print(b.value.decode())

Test yourself

Complete the c_int definition
```
a = ctypes.____(42)
```
Show answer
```
a = ctypes.c_int(42)
```
Match type concepts

c_int

C int
c_char_p

char* pointer
.value

Python value
.decode()

Bytes to text
What does c_char_p(b'x').value return?
```
import ctypes
s = ctypes.c_char_p(b'kutu')
print(s.value)
```
- An error
- A number
- A text string
- A bytes string
Show answer

A bytes string — answer: a bytes string. c_char_p.value returns bytes; decode is needed for text.

Next lesson: argtypes and restype

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