Any C library which defines a macro named max in its standard headers is broken beyond imagination. Fortunately, an easy workaround if you need to support such platforms is to #undef max (and any other problematic macros it defines) after including the system headers and before any of your own headers/code. Note that everyone else … Read more
You can undefine it and define again: #include <iostream> #define AAA 13 int main() { #undef AAA #define AAA 7 std::cout << AAA; } outputs: 7 Please note that statements that start with # are preprocessor directives that are taken care of before the code is even compiled. In this case, this constant AAA will … Read more
Consider this code, #define WIDTH 300 enum econst { eWidth=300 }; const int Width=300; struct sample{}; int main() { sample s; int x = eWidth * s; //error 1 int y = WIDTH * s; //error 2 int z = Width * s; //error 3 return 0; } Obviously each multiplication results in compilation-error, but … Read more
While leaving it blank is the obvious option, I’d go with #define conditional_noop(x) do {} while(0) This trick is obviously no-op, but forces you to write a semicolon after conditional_noop(123).
Aren’t they basically the same? No. Absolutely not. Not even close. Apart from the fact your macro is an int and your constexpr unsigned is an unsigned, there are important differences and macros only have one advantage. Scope A macro is defined by the preprocessor and is simply substituted into the code every time it … Read more
Call the make command this way: make CFLAGS=-Dvar=42 And be sure to use $(CFLAGS) in your compile command in the Makefile. As @jørgensen mentioned, putting the variable assignment after the make command will override the CFLAGS value already defined in the Makefile. Alternatively, you could set -Dvar=42 in another variable than CFLAGS and then reuse … Read more
Since Rust 1.34, you can use extern crate self as my_crate, and use my_crate::Foo instead of $crate::Foo. https://github.com/rust-lang/rust/issues/54647 https://github.com/rust-lang/rust/pull/57407 (Credit: Neptunepink ##rust irc.freenode.net)
If I understand correctly, empty macro argument is allowed since C99 and C++0x(11). C99 6.10.3/4 says: … the number of arguments (including those arguments consisting of no preprocessing tokens) shall equal the number of parameters … and C++ N3290 16.3/4 has the same statement, while C++03 16.3/10 mentions: … any argument consists of no preprocessing … Read more
Rust macros aren’t able to do that. Macros operate at the syntactic level, not at the semantic level. That means that although the compiler knows it has an expression (syntax), it doesn’t know what the type of the expression’s value (semantic) is at the moment the macro is expanded. A workaround would be to pass … Read more