Repeat Code in C Based on Compile time Arguments

Question

Suppose I have a some C code, say, printf("A"); how can I repeat it N number of times based on some compile time argument where N is passed in that compiler argument. e.g gcc -D print=N

Similarly, is there a way where we can pass the range of the loop based on the compile time argument/flag?

The second is easy `for (int i = 0; i < print; ++i) ...` The first could be done in C++ with templates, not sure about C though. — john, Jul 03 '20 at 19:26
See https://stackoverflow.com/questions/6872919/compile-time-loops — Frazzo, Jul 03 '20 at 19:26
Please see [How to pass macro definition from “make” command line arguments (-D) to C source code?](https://stackoverflow.com/questions/9052792/how-to-pass-macro-definition-from-make-command-line-arguments-d-to-c-source) — Weather Vane, Jul 03 '20 at 19:26
C and C++ are different languages and need different answers for this question. — n. m. could be an AI, Jul 03 '20 at 19:32

score 6 · Accepted Answer · answered Jul 03 '20 at 19:25

Simply put it into a loop:

for (int i = 0; i < print; ++i)
  printf("A");

The print symbol will be substituted by the value specified on the compiler command line (e.g. -Dprint=5), so the loop runs the desired amount of times. You can do the same thing with the start value 0 by adding another -D definition to use a different range.

However, print is not a good name for such a macro; it's convention to use a longer name in all caps to avoid collisions with e.g. function names.

score 2 · Answer 2 · edited Sep 22 '20 at 07:42

how can I repeat it N number of times based on some compile time argument where N is passed in that compiler argument

Just generate a C file, perhaps using another script (or metaprogram, that you could write in Guile, GPP, C++ or even C) to generate it. Configure your build automation tool (e.g. GNU make or ninja) accordingly.

Remember, you can #include a generated file.

For examples (of C file generators), see GNU bison or SWIG.

See also this blog (from the late Jacques Pitrat).

You could also be interested in libgccjit.

Repeat Code in C Based on Compile time Arguments

2 Answers2