c-preprocessor

If I could find a way to do something similar to this, I could cut out hundreds of lines of code in my application, and dramatically increase maintainability. Anyone have any ideas? #include <stdio.h> int main( ) { #define include_all_files(root) \ #include #root "1.h" \ #include #root "2.h" \ #include #root "3.h" \ #include #root "4.h" include_all_files( first_library ) include_all_files( second_library ) include_all_files( third_library ) return 0; } EDIT : I appreciate the responses, my example seems to be causing a misdirection in effort, so here is the problem I am actually trying to

Is it possible to put #ifndef at the top of a c file? Basically I need to check whether a certain preprocessor constant was declared when running the program and my program will change accordingly. I need to check if -D DESCENDING_ORDER=1 is added as an argument (doesn't matter what value given). I have this code at the top of my main c file: #ifndef DESCENDING_ORDER int ascending = 1; #else int ascending = 0; #endif Works when compiling by itself, but I get errors when I try compiling with a Makefile, something along the lines of "expected identifier before 'int' for int ascending = 1 .

EDIT: I'm planing to refactor some code, and replace the define with a namespace alias. I can't do this though just because "macros are evil". I need to explain why I want to make the change and what can go wrong if I don't. Leaving aside the stance that "macros are evil", what are the downfalls of #define over a namespace alias? Take the code #define MY_NAMESPACE my_namespace versus namespace MY_NAMESPACE = my_namespace; The reason for having aliases is not in the scope of the question. You can also assume the name of the namespace is unique enough that it doesn't appear anywhere else (i.e.

I was looking through Microsoft's port of OpenSSL on GitHub. One commit caught my eye, and it was Adding Win10 Universal Platform support . In the commit, a partition called WINAPI_FAMILY_ONECORE_APP showed up. However, I'm not finding much about it when searching. There are two hits in English and 22 hits in Chinese (see below). Following What’s new in Visual Studio Tools for Windows 10 Preview provides some quasi-bullet points with no explanations: new API partition WINAPI_FAMILY_ONECORE_APP ARM 64 Universal CRT ... I have two questions: What is WINAPI_FAMILY_ONECORE_APP , and how is it

I am trying to understand implement a print once function, this code is working fine; But I am not able to understand some things: 1) How blockwise this is working? Maybe I am not able to clear it properly, but just want to know, what property of C make this happen? 1 #include <stdio.h> 2 3 #define _TRACE_ 4 5 #ifdef _TRACE_ 6 #define print_once(fmt, ...) \ 7 ({ \ 8 static bool __print_once=false; \ 9 if(!__print_once) { \ 10 __print_once = true; \ 11 do { \ 12 printf(fmt, ##__VA_ARGS__); \ 13 }while(0); \ 14 } \ 15 }) 16 #else 17 #define print_once(fmt, ...) \ 18 printf("\n"); 19 #endif 20 21

This question already has an answer here: What are the applications of the ## preprocessor operator and gotchas to consider? 13 answers The ## operator in C 7 answers What's the meaning of "##" in the following? #define CC_SYNTHESIZE(varType, varName, funName)\ protected: varType varName;\ public: inline varType get##funName(void) const { return varName; }\ public: inline void set##funName(varType var){ varName = var; } The operator ## concatenates two arguments leaving no blank spaces between them: e.g. #define glue(a,b) a ## b glue(c,out) << "test"; This would also be translated into: cout <