There is a null-terminated ASCII string existing in the address space of the target process under debugging. I want to write a WinDbg script to print out the length of this string. Assuming I know the address of the starting character of the string, how do I calculate its length?
IMHO it's not convenient in WinDbg and I tried finding a solution involving s, .foreach and .if for more than 15 minutes but the result was frustrating. In such a case I use a real programming language like Python with PyKD.
Save the following into a file strlen.py:
from pykd import *
import sys
addr = int(sys.argv[1], 16)
length = 0
while(0 != loadBytes(addr+length, 1)[0]):
length += 1
dprintln(str(length))
Then run it with the address as argument:
0:022> !py c:\tmp\strlen.py 773a004e
43
0:022> db 773a004e L0n44
773a004e 54 68 69 73 20 70 72 6f-67 72 61 6d 20 63 61 6e This program can
773a005e 6e 6f 74 20 62 65 20 72-75 6e 20 69 6e 20 44 4f not be run in DO
773a006e 53 20 6d 6f 64 65 2e 0d-0d 0a 24 00 S mode....$.
Note that PyKd does not automatically convert named symbols to addresses (e.g. you can't pass ntdll as an address)