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The C preprocessor is a siren song, lures people in with the promise of "extra performance/features/structures for zero runtime cost!" but murders any readabili

The C preprocessor is a siren song, lures people in with the promise of "extra performance/features/structures for zero runtime cost!" but murders any readability or rationality within your codebase. Cool concept, but once you've dealt with any legacy codebase that has used it extensively, it feels like an anti-pattern/footgun. Ultimately you just want the language to do those things directly and for the compiler to be smart enough to optimize it later. Essentially it is too clever for its own good.

lupire 5y ago
No one likes the preprocessor, but it's practicaly required if you don't want to move to C++ with template metaprogramming.
- marcosdumay 5y ago
  Well, C++ templates happen on the preprocessor too.
  - adrianN 5y ago
    No they don't. Template instantiation happens during compilation, way later than the preprocessor.
  - kllrnohj 5y ago
    Not really? They're part of compilation and obey all the type rules & syntax of the language. They're not textual replacements that run in a distinctly different phase like macros are.
  - jcelerier 5y ago
    where in hell did you learn that, this is entirely false
    - __d 5y ago
      Well, it is today. When I first learned C++, using cfront in the late 80's, lots of the language was implemented as C pre-processor macros.
      - jcelerier 5y ago
        maybe lots of the language, but not templates. Cfront 2 did not have templates, and Cfront 3 did have them without using the preprocessor. You can even check out how it was done: https://github.com/seyko2/cfront-3/blob/master/src/template.C https://github.com/seyko2/cfront-3/blob/master/src/template....
- badsectoracula 5y ago
  I do like the preprocessor and my major pet peeve with C is that the preprocessor has been stagnant for ages. Like, why the hell can't i do something like #define BASE hey #define HEADERS foo bar baz #append HEADERS bad bal bah #push OSSUFFIX #ifdef WIN32 #define OSSUFFIX win32 #else #define OSSUFFIX unknown #endif #foreach H HEADERS #eval include "$(BASE)/$(OSSUFFIX)/$(HEADERS)" #endfor #pop OSSUFFIX People go to great lengths making all sorts of weird structures from x-macros, repeated statements, defines that only exist to be used by other defines, etc all to work around existing preprocessor limitations - and many of them would simply become unnecessary if the preprocessor could do things like variable editing, loops and being able to eval its own commands. Even though some stuff can be done via language features, it is often necessary and more flexible to work with the source code itself.
  - midjji 5y ago
    One alternative is to just write a C code generator, which lets you mix C and some sensible language, eg. python. Then use that to generate the code which is then sent to gcc.
midjji 5y ago
Its not too clever for its own good, its programmers that are too clever for C, and desperately need basic features, and its the only way to get them unless you switch language. Its also surreally poorly designed, encouraging worse habits than C itself. Avoiding definition collisions and lack of namespaces alone make it horrific for any moderate sized project and up. Combine that with the near complete lack of static analysis tools, and its a recipe for disaster.

lupire 5y ago

No one likes the preprocessor, but it's practicaly required if you don't want to move to C++ with template metaprogramming.

marcosdumay 5y ago
Well, C++ templates happen on the preprocessor too.
- adrianN 5y ago
  No they don't. Template instantiation happens during compilation, way later than the preprocessor.
- kllrnohj 5y ago
  Not really? They're part of compilation and obey all the type rules & syntax of the language. They're not textual replacements that run in a distinctly different phase like macros are.
- jcelerier 5y ago
  where in hell did you learn that, this is entirely false
  - __d 5y ago
    Well, it is today. When I first learned C++, using cfront in the late 80's, lots of the language was implemented as C pre-processor macros.
    - jcelerier 5y ago
      maybe lots of the language, but not templates. Cfront 2 did not have templates, and Cfront 3 did have them without using the preprocessor. You can even check out how it was done: https://github.com/seyko2/cfront-3/blob/master/src/template.C https://github.com/seyko2/cfront-3/blob/master/src/template....
badsectoracula 5y ago
I do like the preprocessor and my major pet peeve with C is that the preprocessor has been stagnant for ages. Like, why the hell can't i do something like #define BASE hey #define HEADERS foo bar baz #append HEADERS bad bal bah #push OSSUFFIX #ifdef WIN32 #define OSSUFFIX win32 #else #define OSSUFFIX unknown #endif #foreach H HEADERS #eval include "$(BASE)/$(OSSUFFIX)/$(HEADERS)" #endfor #pop OSSUFFIX People go to great lengths making all sorts of weird structures from x-macros, repeated statements, defines that only exist to be used by other defines, etc all to work around existing preprocessor limitations - and many of them would simply become unnecessary if the preprocessor could do things like variable editing, loops and being able to eval its own commands. Even though some stuff can be done via language features, it is often necessary and more flexible to work with the source code itself.
- midjji 5y ago
  One alternative is to just write a C code generator, which lets you mix C and some sensible language, eg. python. Then use that to generate the code which is then sent to gcc.

midjji 5y ago

Its not too clever for its own good, its programmers that are too clever for C, and desperately need basic features, and its the only way to get them unless you switch language. Its also surreally poorly designed, encouraging worse habits than C itself. Avoiding definition collisions and lack of namespaces alone make it horrific for any moderate sized project and up. Combine that with the near complete lack of static analysis tools, and its a recipe for disaster.