The #ifdef directive is used to check if a preprocessor symbol is defined. The standard (C11 6.4.2 Identifiers) mandates that identifiers must not start with a digit: identifier: identifier-nondigit identifier identifier-nondigit identifier digit identifier-nondigit: nondigit universal-character-name other implementation-defined characters> nondigit: one of _ a b c d e f g h i j k l … Read more
You could try typeid(T).name() Edit: Fixed based on comments.
I am working on a large project that involves a lot of preprocessor macro functions to synthesize any code that cannot be replaced by templates. Believe me, I am familiar with all sorts of template tricks, but as long as there is no standardized, type safe metaprogramming language that can directly create code, we will … Read more
Soma macro magic: #define DO_EXPAND(VAL) VAL ## 1 #define EXPAND(VAL) DO_EXPAND(VAL) #if !defined(MYVARIABLE) || (EXPAND(MYVARIABLE) == 1) Only here if MYVARIABLE is not defined OR MYVARIABLE is the empty string #endif Note if you define MYVARIABLE on the command line the default value is 1: g++ -DMYVARIABLE <file> Here the value of MYVARIABLE is the … Read more
The C++ standard headers do not have a “.h” suffix. I believe the reason is that there were many, different pre-standard implementations that the standard would break. So instead of requiring that vendors change their exiting “iostream.h” (for example) header to be standards compliant (which would break their existing user’s code), the standards committee decided … Read more
Macro names should only consist of alphanumeric characters and underscores, i.e. ‘a-z’, ‘A-Z’, ‘0-9’, and ‘_’, and the first character should not be a digit. Some preprocessors also permit the dollar sign character ‘$’, but you shouldn’t use it; unfortunately I can’t quote the C standard since I don’t have a copy of it. From … Read more
You can use the preprocessor directive #pragma message. Example: #define STR_HELPER(x) #x #define STR(x) STR_HELPER(x) #define AAA 123 #pragma message “content of AAA: ” STR(AAA) int main() { return 0; } The output may look like this: $ gcc test.c test.c:5:9: note: #pragma message: content of AAA: 123 #pragma message(“content of AAA: ” STR(AAA)) ^ … Read more
Project Settings -> C/C++ -> Preprocessor -> Preprocessor definitions Here you can define symbols that are applied globally to all source code in your project.
. separates tokens and so you can’t use ## as .red is not a valid token. You would only use ## if you were concatenating two tokens into a single one. This works: #define X(a, b) foo.a = -1; What’s a valid proprocessing token? Can someone explain this? It is what gets parsed/lexed. foo.bar would … Read more
The xstr macro defined below will stringify after doing macro-expansion. #define xstr(a) str(a) #define str(a) #a #define RECORDS_PER_PAGE 10 #define REQUEST_RECORDS \ “SELECT Fields FROM Table WHERE Conditions” \ ” OFFSET %d * ” xstr(RECORDS_PER_PAGE) \ ” LIMIT ” xstr(RECORDS_PER_PAGE) “;”