Tuesday 3 February 2004 — This is close to 21 years old. Be careful.
A co-worker had a mysterious C++ compile error: a symbol was undefined, but it was clearly present in the header file. We figured there was an ifdef affecting it, but how to find the culprit in the 11,000-line header file?
I tossed off this Python script:
# showifstruct.py
import re, sys
reDirective = re.compile(r'\s*#\s*([a-z]+)')
f = file(sys.argv[1])
targetLnum = int(sys.argv[2])
# A stack. Each element is a list of tuples.
# Each tuple is a linenumber/text pair of a directive that affects the current line.
ifstack = []
lnum = 0
for l in f.readlines():
lnum += 1
if lnum == targetLnum:
break
matchDir = reDirective.match(l)
if matchDir:
directive = matchDir.group(1)
if directive in ['if', 'ifdef', 'ifndef']:
# Start a group
ifstack.append( [[lnum, l]] )
elif directive == 'else':
ifstack[-1].append( [lnum, l] )
elif directive == 'endif':
del ifstack[-1]
indent = ''
for ifs in ifstack:
for lnum, line in ifs:
print "%6d: %s%s" % (lnum, indent, line),
indent += ' '
Give it a file name and a line number, and it will track what preprocessor directives affect the line in question. It prints the lines that matter, indented to show structure, with line numbers:
$ showifstruct WinUser.h 11100
12: #ifndef _WINUSER_
10384: #if(WINVER >= 0x0500)
10483: #ifndef NOWINABLE
Comments
A minor nit - instead of this:
del ifstack[-1]
you could do this:
ifstack.pop()
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