Sending null terminated string to my C code through Python

Question

I am sending strings to my BPF C code and I am not sure if the strings passed in are null-terminated. If they are not, is there a way to make them null terminated? I am sending in my lines of code to BPF so I can count them manually using my stringCounter function but I keep hitting a forever loop sadly. Here is what my Python code looks like:

b = BPF(src_file="hello.c")

lookupTable = b["lookupTable"]
#add hello.csv to the lookupTable array
f = open("hello copy.csv","r")
contents = f.readlines()
for i in range(0,len(contents)):
    string = contents[i].encode('utf-8')
    lookupTable[ctypes.c_int(i)] = ctypes.create_string_buffer(string, len(string))

And here is the code I found for my null terminated string counter

int stringLength(char* txt)
{
    int i=0,count=0;
    
    while(txt[i++]!='\0'){
        count+=1;
    }
    
    return count;
}

Answer 1

ctypes.create_string_buffer(string, len(string)) is not zero-terminated. But ctypes.create_string_buffer(string) is. It's easy to see that, since ctypes.create_string_buffer(string)[-1] is b'\x00', whereas ctypes.create_string_buffer(string, len(string))[-1] is the last byte in string.

In other words, if you want a zero-terminated buffer, let create_string_buffer figure out the length. (It uses the actual length from the Python bytes object, so it doesn't get fooled by internal NUL bytes, if you were worried about that.)