As far as I know, what you're trying to do (use if statement and then return a value from a macro) isn't possible in ISO C... but it is somewhat possible with statement expressions (GNU extension).

May 14, 2011 · Most compilers will allow you to define a macro from the command line (e.g. g++ -DDEBUG something.cpp), but you can also just put a define in your code like so: #define DEBUG Some resources: Wikipedia article; C++ specific site; Documentation on GCC's preprocessor; Microsoft reference; C specific site (I don't think it's different from the C++ ...

These two aren't equivalent: * In the first example, 'b' is still a positional argument that must be provided: * in the second example, 'b' is a true optional argument that can be ommitted (and in this case will have the value None if ommitted).

Oct 28, 2009 · #define is a compiler pre processor directive and should be used as such, for conditional compilation etc.. E.g. where low level code needs to define some possible alternative data structures for portability to specif hardware. It can produce inconsistent results depending on the order your modules are compiled and linked.

Sep 11, 2009 · Define the type of an object, which may be built-in or a class or struct. Declare the name of an object, so anything with a name has been declared which includes Variables, Funtions, etc. A class or struct allows you to change how objects will be defined when it …

May 10, 2010 · In the normal C or C++ build process the first thing that happens is that the PreProcessor runs, the preprocessor looks though the source files for preprocessor directives like #define or #include and then performs simple operations with them. in the case of a #define directive the preprocessor does simple text based substitution.

Jul 9, 2018 · #define is part of something called the "preprocessor." Essentially, this is the code that is processed before the C document is compiled. Most of the preprocessor code is in a file with a ".h" extension (which is why you may have seen that when importing libraries). The preprocessor language is primitive.

Nov 13, 2009 · /* Define _USE_MATH_DEFINES before including math.h to expose these macro * definitions for common math constants. These are placed under an #ifdef * since these commonly-defined names are not part of the C/C++ standards.

Feb 12, 2021 · Statements defined using #define are called macros. And macros are used in a multitude of uses. We can use them to conditionally compile sections of code. #ifdef ONE int AddOne(int x) { return x + 1; } #else int AddTwo(int x) { return x + 2; } #endif When we don't need to store constants in a variable. #define MAX_BOUND 1000 #define MIN_BOUND 10

#define is a preprocessor operation and will cause all occurrences of m to be replaced by 30000 before the compilation phase happens. The other two examples are bona fide variables. The other two examples are bona fide variables.