10.9 Caveats of using protoize
The conversion programs protoize and unprotoize can
sometimes change a source file in a way that won't work unless you
rearrange it.
- protoize can insert references to a type name or type tag before
the definition, or in a file where they are not defined.
If this happens, compiler error messages should show you where the new
references are, so fixing the file by hand is straightforward.
- There are some C constructs which protoize cannot figure out.
For example, it can't determine argument types for declaring a
pointer-to-function variable; this you must do by hand. protoize
inserts a comment containing `???' each time it finds such a
variable; so you can find all such variables by searching for this
string. ISO C does not require declaring the argument types of
pointer-to-function types.
- Using unprotoize can easily introduce bugs. If the program
relied on prototypes to bring about conversion of arguments, these
conversions will not take place in the program without prototypes.
One case in which you can be sure unprotoize is safe is when
you are removing prototypes that were made with protoize; if
the program worked before without any prototypes, it will work again
without them.
You can find all the places where this problem might occur by compiling
the program with the -Wconversion option. It prints a warning
whenever an argument is converted.
- Both conversion programs can be confused if there are macro calls in and
around the text to be converted. In other words, the standard syntax
for a declaration or definition must not result from expanding a macro.
This problem is inherent in the design of C and cannot be fixed. If
only a few functions have confusing macro calls, you can easily convert
them manually.
- protoize cannot get the argument types for a function whose
definition was not actually compiled due to preprocessing conditionals.
When this happens, protoize changes nothing in regard to such
a function. protoize tries to detect such instances and warn
about them.
You can generally work around this problem by using protoize step
by step, each time specifying a different set of -D options for
compilation, until all of the functions have been converted. There is
no automatic way to verify that you have got them all, however.
- Confusion may result if there is an occasion to convert a function
declaration or definition in a region of source code where there is more
than one formal parameter list present. Thus, attempts to convert code
containing multiple (conditionally compiled) versions of a single
function header (in the same vicinity) may not produce the desired (or
expected) results.
If you plan on converting source files which contain such code, it is
recommended that you first make sure that each conditionally compiled
region of source code which contains an alternative function header also
contains at least one additional follower token (past the final right
parenthesis of the function header). This should circumvent the
problem.
- unprotoize can become confused when trying to convert a function
definition or declaration which contains a declaration for a
pointer-to-function formal argument which has the same name as the
function being defined or declared. We recommend you avoid such choices
of formal parameter names.
- You might also want to correct some of the indentation by hand and break
long lines. (The conversion programs don't write lines longer than
eighty characters in any case.)
