How much effort are you willing to go to? There’s an obnoxiously obscure way to do it but it requires you to set up a dummy directory to hold surrogates for the system headers. OTOH, it doesn’t require any changes in any of your source code. The same technique works equally well for C code. … Read more
Text inside an ifdef/endif or ifndef/endif pair will be left in or removed by the pre-processor depending on the condition. ifdef means “if the following is defined” while ifndef means “if the following is not defined”. So: #define one 0 #ifdef one printf(“one is defined “); #endif #ifndef one printf(“one is not defined “); #endif … Read more
My initial reaction was #ifdef, of course, but I think #if actually has some significant advantages for this – here’s why: First, you can use DEBUG_ENABLED in preprocessor and compiled tests. Example – Often, I want longer timeouts when debug is enabled, so using #if, I can write this DoSomethingSlowWithTimeout(DEBUG_ENABLED? 5000 : 1000); … instead … Read more
In C, string literals are concatenated automatically. For example, const char * s1 = “foo” “bar”; const char * s2 = “foobar”; s1 and s2 are the same string. So, for your problem, the answer (without token pasting) is #ifdef __TESTING #define IV_DOMAIN “example.org” #elif __LIVE_TESTING #define IV_DOMAIN “test.example.com” #else #define IV_DOMAIN “example.com” #endif #define … Read more
Quote Wikipedia: Variable-argument macros were introduced in 1999 in the ISO/IEC 9899:1999 (C99) revision of the C language standard, and in 2011 in ISO/IEC 14882:2011 (C++11) revision of the C++ language standard. So it’s standard from C99 and C++11 onwards, but a GNU extension in C++03.
He who is Shy* gave you the germ of an answer, but only the germ. The basic technique for converting a value into a string in the C pre-processor is indeed via the ‘#’ operator, but a simple transliteration of the proposed solution gets a compilation error: #define TEST_FUNC test_func #define TEST_FUNC_NAME #TEST_FUNC #include <stdio.h> … Read more
gcc -E file.c or g++ -E file.cpp will do this for you. The -E switch forces the compiler to stop after the preprocessing phase, spitting all it’s got at the moment to standard output. Note: Surely you must have some #include directives. The included files get preprocessed, too, so you might get lots of output. … Read more
There is no difference in both. In first case XXX is replaced by yyy and by (yyy) is second case. The convention to use brackts is to avoid logical errors that may occur. For example you define addition function as: #define f(N) N+N int a = f(5)*f(5) Expected value is 10*10 = 100 , but … Read more
The offsetof() macro is a compile-time construct. There is no standard-compliant way to define it, but every compiler must have some way of doing it. One example would be: #define offsetof( type, member ) ( (size_t) &( ( (type *) 0 )->member ) ) While not being a compile-time construct technically (see comments by user … Read more
Because sizeof is evaluated at compilation time while directives are evaluated before compilation, and the part that does that is not the compiler, so it won’t understand what sizeof means.