Tell me more ×
Stack Overflow is a question and answer site for professional and enthusiast programmers. It's 100% free, no registration required.
up vote 0 down vote favorite

I'm trying to do a simple VB6 to c translator to help me port an open source game to the c language. I want to be able to get "NpcList[NpcIndex]" from "With Npclist[NpcIndex]" using ragex and to replace it everywhere it has to be replaced. ("With" is used as a macro in VB6 that adds Npclist[NpcIndex] when ever it needs to until it founds "End With")

Example:
 With Npclist[NpcIndex]
 .goTo(245) <-- it should be replaced with Npclist[NpcIndex].goTo(245)
 End With

Is it possible to use regex to do the job? I've tried using a function to perfom another regex replace between the "With" and the "End With" but I can't know the text the "With" is replacing (Npclist[NpcIndex]). Thanks in advance

share|improve this question
what's wrong about automatic tools (google.com/search?q=convert+vb+to+c)? – deathApril Apr 22 at 18:59
VB to c converters are mostly VB.net to C# converters, I just want to make a simple script to help me replacing some common stuff so I can then improve the code faster. – Lautaro Apr 22 at 19:24

3 Answers

up vote 1 down vote accepted

I personally wouldn't trust any single-regex solution to get it right on the first time nor feel like debugging it. Instead, I would parse the code line-to-line and cache any With expression to use it to replace any . directly preceded by whitespace or by any type of brackets (add use-cases as needed):

(?<=[\s[({])\. - positive lookbehind for any character from the set + escaped literal dot

(?:(?<=[\s[({])|^)\. - use this non-capturing alternatives list if to-be-replaced . can occur on the beginning of line

import re

def convert_vb_to_c(vb_code_lines):
    c_code = []
    current_with = ""
    for line in vb_code_lines:
        if re.search(r'^\s*With', line) is not None:
            current_with = line[5:] + "."
            continue
        elif re.search(r'^\s*End With', line) is not None:
            current_with = "{error_outside_with_replacement}"
            continue
        line = re.sub(r'(?<=[\s[({])\.', current_with, line)
        c_code.append(line)
    return "\n".join(c_code)


example = """
With Npclist[NpcIndex]
    .goTo(245)
End With
With hatla
    .matla.tatla[.matla.other] = .matla.other2
    dont.mind.me(.do.mind.me)
    .next()
End With
"""
# use file_object.readlines() in real life
print(convert_vb_to_c(example.split("\n")))
share|improve this answer
Altough I wasn't etirely with regex, I really liked the solution. Thanks! – Lautaro Apr 23 at 2:53
1  
Nice solution. Unlike my answer, it handles multiple lines between the With/End With. You might want to use if re.search(r'^\s*With', line) is not None and elif re.search(r'Ends With\s*$', line) is not None so it doesn't break when lines have extraneous whitespace. – alan 2 days ago
@alan good point, thanks :) I didn't want to match ' commented End With though... – deathApril 2 days ago
up vote 0 down vote

You can pass a function to the sub method:

# just to give the idea of the regex
regex = re.compile(r'''With (.+)
(the-regex-for-the-VB-expression)+?
End With''')

def repl(match):
    beginning = match.group(1)  # NpcList[NpcIndex] in your example
    return ''.join(beginning + line for line in match.group(2).splitlines())

re.sub(regex, repl, the_string)

In repl you can obtain all the information about the matching from the match object, build whichever string you want and return it. The matched string will be replaced by the string you return.

Note that you must be really careful to write the regex above. In particular using (.+) as I did matches all the line up to the newline excluded, which or may not be what you want(but I don't know VB and I have no idea which regex could go there instead to catch only what you want.

The same goes for the (the-regex-forthe-VB-expression)+. I have no idea what code could be in those lines, hence I leave to you the detail of implementing it. Maybe taking all the line can be okay, but I wouldn't trust something this simple(probably expressions can span multiple lines, right?).

Also doing all in one big regular expression is, in general, error prone and slow.

I'd strongly consider regexes only to find With and End With and use something else to do the replacements.

share|improve this answer
I want to know if regex is able to find the "With" string and after that use it as if was the macro replacing the .something with the (Thing the replace found after while).something each time it appears until it finds End With. I just could identify the with and just read after it ends but I wanted to know if it was possible. – Lautaro Apr 22 at 19:28
NpcList[NpcIndex] and .goTo(245) are just examples, not exact strings to be matched – deathApril Apr 22 at 20:26
up vote 0 down vote

This may do what you need in Python 2.7. I'm assuming you want to strip out the With and End With, right? You don't need those in C.

>>> import re
>>> search_text = """
... With Np1clist[Npc1Index]
...  .comeFrom(543)
... End With
...
... With Npc2list[Npc2Index]
...  .goTo(245)
... End With"""
>>>
>>> def f(m):
...     return '{0}{1}({2})'.format(m.group(1), m.group(2), m.group(3))
...
>>> regex = r'With\s+([^\s]*)\s*(\.[^(]+)\(([^)]+)\)[^\n]*\nEnd With'
>>> print re.sub(regex, f, search_text)

Np1clist[Npc1Index].comeFrom(543)

Npc2list[Npc2Index].goTo(245)
share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.