You can simulate conditionals using macro token concatenation as follows: #define DEF_CONST(b_const) DEF_CONST_##b_const #define DEF_CONST_true const #define DEF_CONST_false Then, /* OK */ DEF_CONST(true) int x; /* expands to const int x */ DEF_CONST(false) int y; /* expands to int y */ /* NOT OK */ bool bSomeBool = true; // technically not C 🙂 DEF_CONST(bSomeBool) … Read more
It should be noted that MSVC uses the syntax: #pragma message ( “your warning text here” ) The usual #warning syntax generates a fatal error C1021: invalid preprocessor command ‘warning’ so it is not portable to those compilers.
The simple explanation would be that the standard requires assert to be a macro, if we look at the draft C99 standard(as far as I can tell the sections are the same in draft C11 standard as well) section 7.2 Diagnostics paragraph 2 says: The assert macro shall be implemented as a macro, not as … Read more
While a preprocessor macro is being expanded, that macro’s name is not expanded. So all three of your symbols are defined as themselves: ONE -> TWO -> THREE -> ONE (not expanded because expansion of ONE is in progress) TWO -> THREE -> ONE -> TWO ( ” TWO ” ) THREE -> ONE -> … Read more
The C++ Standard says (16.3.4.3): The resulting completely macro-replaced preprocessing token sequence [… of the macro expansion…] is not processed as a preprocessing directive even if it resembles one… So no, there is no ‘official’ way of achieving what you want with macros.
It looks like a way to statically ensure that name is a string literal and not some other type. If you do (void)”” “hello”; then it is a valid C expression. But if you do something like (void)”” 1; then you get a syntax error.
The text replacement is done where the macro is used, not where you wrote the #define. At the point you use FOO, it replaces FOO with NUM and NUM is currently defined to be 20.
What you need to do is have the preprocessor generate reflection data about the fields. This data can be stored as nested classes. First, to make it easier and cleaner to write it in the preprocessor we will use typed expression. A typed expression is just an expression that puts the type in parenthesis. So … Read more
Yes! (well, sort of) There are a couple publicly available tools to help you out. Both use preprocessor code generation to create templates which implement the custom operators. These operators consist of one or more built-in operators in conjunction with an identifier. Since these aren’t actually custom operators, but merely tricks of operator overloading, there … Read more
The __llvm__ and __clang__ macros are the official way to check for an LLVM compiler (llvm-gcc or clang) or clang, respectively. __has_feature and __has_builtin are the recommended way of checking for optional compiler features when using clang, they are documented here. Note that you can find a list of the builtin compiler macros for gcc, … Read more
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