Why would somebody use an #if 1 C preprocessor directive?

Question

I am looking through some C source code and I don\'t understand the following part

#if 1

   typedef u         


        

Answer 1

For experimenting with various code paths.

Answer 2

It's another way of saying for #if true it was most likely a result of code that was previously checking for another symbol then refactored to always be true.

Answer 3

The cleaner way of doing it is probably doing something like:

#if ALGO1

#else

#endif

But, you will have to pass in ALGO1 to the compiler args somewhere...for example in a makefile, you need to add -DALGO1=1 (if no 1 is provided, 1 is assumed). Ref: http://www.amath.unc.edu/sysadmin/DOC4.0/c-compiler/user_guide/cc_options.doc.html

This is more work...so, usually, for quick checks, #if 1 is used. And in some cases, forgotten and left behind as well :-)