2018年3月28日 · 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++ ...

I'm trying to make a macro with the following formula: (a^2/(a+b))*b, and I want to make sure that the there will be no dividing by zero.

2017年3月4日 · #define simply substitutes a name with its value. Furthermore, a #define'd constant may be used in the preprocessor: you can use it with #ifdef to do conditional compilation based on its value, or use the stringizing operator # to get a string with its value. And as the compiler knows its value at compile time it may optimize code based on that ...

In other words, when the compiler starts building your code, no #define statements or anything like that is left. A good way to understand what the preprocessor does to your code is to get hold of the preprocessed output and look at it.

Probably a naïve question - I used to program 20 years ago and haven't coded much since. My memory of how the C preprocessor works has atrophied significantly since then...

2014年3月11日 · #define mkstr(s) #s mkstr(foo) // is the same as "foo" So in your case, #define PROJX(id) "..\\" #id "_data_var.h" #define PROJ(id) PROJX(id) #define PROJECT PROJ(ID) might be one way to go. Another alternative is. #define mkstrX(s) #s #define mkstr(s) mkstrX(s) #define PROJECT "..\\" mkstr(ID) "_data_var.h" which does the same, getting a result of

You could indeed perform those check, at the cost of increased volume and complexity of code. The pythonic way is to assume the happy path (all types correct) is being followed, and cross the bridge of handling any errors when they become obvious (i.e. when the code raises an exception).

That file can then #ifdef _PASS2/#else to define macros for all the variables that should be different on the two passes. Even though the code gets generated twice, on some micros that will take less space than using the arrow operator with passed-in pointers.

2009年10月28日 · #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.

2008年8月19日 · #define is used to define compile-time constants that you can use with #if to include or exclude bits of code. #define USEFOREACH #if USEFOREACH foreach(var item in items) { #else for(int i=0; i < items.Length; ++i) { var item = items[i]; //take item #endif doSomethingWithItem(item); }