Converting python string object to c char* using ctypes

I am trying to send 2 strings from Python (3.2) to C using ctypes. This is a small part of my project on my Raspberry Pi. To test if the C function received the strings correctly, I place one of them in a text file.

**Python code**

<!-- language: lang-python -->

string1 = "my string 1"
string2 = "my string 2"

# create byte objects from the strings
b_string1 = string1.encode('utf-8')
b_string2 = string2.encode('utf-8')

# send strings to c function
my_c_function(ctypes.create_string_buffer(b_string1),
ctypes.create_string_buffer(b_string2))

**C code**

<!-- language: lang-c -->

void my_c_function(const char* str1, const char* str2)
{
// Test if string is correct
FILE *fp = fopen("//home//pi//Desktop//out.txt", "w");
if (fp != NULL)
{
fputs(str1, fp);
fclose(fp);
}

// Do something with strings..
}

**The problem**

Only the first letter of the string appears in the text file.

I've tried many ways to convert the Python string object with ctypes.

- ctypes.c_char_p
- ctypes.c_wchar_p
- ctypes.create_string_buffer

With these conversions I keep getting the error "wrong type" or "bytes or integer address expected instead of str instance".

I hope someone can tell me where it goes wrong.
Thanks in advance.

Have you considered using [SWIG](

[To see links please register here]

)? I haven't tried it myself but here's what it would look like, without changing your C source:

/*mymodule.i*/

%module mymodule
extern void my_c_function(const char* str1, const char* str2);

This would make your Python source as simple as (skipping compilation):

import mymodule

string1 = "my string 1"
string2 = "my string 2"
my_c_function(string1, string2)

Note I'm not certain `.encode('utf-8')` is necessary if your source file is already UTF-8.

I think you just need to use c_char_p() instead of create_string_buffer().

string1 = "my string 1"
string2 = "my string 2"

# create byte objects from the strings
b_string1 = string1.encode('utf-8')
b_string2 = string2.encode('utf-8')

# send strings to c function
my_c_function(ctypes.c_char_p(b_string1),
ctypes.c_char_p(b_string2))

If you need mutable strings then use create_string_buffer() and cast those to c_char_p using ctypes.cast().

Thanks to Eryksun the solution:

**Python code**

string1 = "my string 1"
string2 = "my string 2"

# create byte objects from the strings
b_string1 = string1.encode('utf-8')
b_string2 = string2.encode('utf-8')

# send strings to c function
my_c_function.argtypes = [ctypes.c_char_p, ctypes.char_p]
my_c_function(b_string1, b_string2)