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https://github.com/pix/cppp

Fork of cppp: A Partial Preprocessor for C from Brian Raiter
https://github.com/pix/cppp

Last synced: 16 days ago
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Fork of cppp: A Partial Preprocessor for C from Brian Raiter

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README 

        
cppp is a partial preprocessor for C/C++ code. It implements enough of

the C preprocessor to identify the preprocessor statements #if,

#ifdef, et al., and applies their effects for the identifiers that are

specified on the command-line. Preprocessor statements using

identifiers not specified by the user are passed through without

modification. And no other part of the input is altered.



Thus, if cppp is invoked with the options -DFOO -UBAR, then FOO will

be defined, BAR will be undefined, and all other identifiers will be

unaffected. A section guarded by "#ifdef FOO" will be included in the

output without the guard statements, and a section guarded by "#ifdef

BAR" will be entirely dropped from the output.



In addition to removing #ifdef statements, cppp understands complex

expressions in #if statements that involve the defined operator, and

will apply the effects even partially. Thus for example the

preprocessor statement "#if (defined(BAR) || defined(BAZ))" would be

edited to read "#if defined(BAZ)" in the output.



cppp can also handle simple numeric tests. For example, giving cppp

the option -D_LIB_VERSION=5 would cause the preprocessor statement

"#if _LIB_VERSION >= 4" to succeed. Note, however, that cppp is

limited to dealing with integer constants. The preprocessor statement

"#if _LIB_VERSION >= _HEADER_FILE_VERSION" would simply get rewritten

to "#if 5 >= _HEADER_FILE_VERSION", even if a definition for

_HEADER_FILE_VERSION was provided in the same file.



The general purpose of this program is to deal with legacy code bases

where #ifdefs have crept in and infiltrated the source. This sort of

thing usually happens while code is transitioning from one platform to

another, in the misguided belief that this will ease the process

rather than make it more confusing. Then, if the time finally comes

that the ifdefs can be safely removed, it often doesn't get done

because it's too tedious and error-prone to do it manually.



I originally wrote cppp as an interesting exercise, but I later wound

up using it to save myself from just such a tedious task. Sadly,

because the code was not originally intended to be seen by anyone, it

is not well-written and in some places it is downright opaque. I have

attempted to ameliorate this by cleaning up some of the most egregious

inconsistencies and adding a handful of comments, but the central

functions are quite large and not easily explicated (particularly with

all the intervening years since the time of its original creation). I

offer it solely as a tool that might save you from a mind-numbing

chore, but not as something to learn from.



Brian Raiter

[email protected]

June, 2011