Text inside an ifdef/endif or ifndef/endif pair will be left in or removed by the pre-processor depending on the condition. ifdef means “if the following is defined” while ifndef means “if the following is not defined”. So: #define one 0 #ifdef one printf(“one is defined “); #endif #ifndef one printf(“one is not defined “); #endif … Read more
Your usage example container_of(dev, struct wifi_device, dev); might be a bit misleading as you are mixing two namespaces there. While the first dev in your example refers to the name of pointer the second dev refers to the name of a structure member. Most probably this mix up is provoking all that headache. In fact … Read more
There is a very solid reason for this: const in C does not mean something is constant. It just means a variable is read-only. In places where the compiler requires a true constant (such as for array sizes for non-VLA arrays), using a const variable, such as fieldWidth is just not possible.
Go to your Target or Project settings, click the Gear icon at the bottom left, and select “Add User-Defined Setting”. The new setting name should be GCC_PREPROCESSOR_DEFINITIONS, and you can type your definitions in the right-hand field. Per Steph’s comments, the full syntax is: constant_1=VALUE constant_2=VALUE Note that you don’t need the ‘=’s if you … Read more
Use the preprocessor # operator: #define CALL_DO_SOMETHING(VAR) do_something(#VAR, VAR);
Classical C preprocessor question…. #define STR_HELPER(x) #x #define STR(x) STR_HELPER(x) #define MAJOR_VER 2 #define MINOR_VER 6 #define MY_FILE “/home/user/.myapp” STR(MAJOR_VER) STR(MINOR_VER) The extra level of indirection will allow the preprocessor to expand the macros before they are converted to strings.
I don’t think there is a way to do variable length string comparisons completely in preprocessor directives. You could perhaps do the following though: #define USER_JACK 1 #define USER_QUEEN 2 #define USER USER_JACK #if USER == USER_JACK #define USER_VS USER_QUEEN #elif USER == USER_QUEEN #define USER_VS USER_JACK #endif Or you could refactor the code a … Read more
Macros are just like any other tool – a hammer used in a murder is not evil because it’s a hammer. It is evil in the way the person uses it in that way. If you want to hammer in nails, a hammer is a perfect tool. There are a few aspects to macros that … Read more
If you’re using c99 or c++0x there is the pragma operator, used as _Pragma(“argument”) which is equivalent to #pragma argument except it can be used in macros (see section 6.10.9 of the c99 standard, or 16.9 of the c++0x final committee draft) For example, #define STRINGIFY(a) #a #define DEFINE_DELETE_OBJECT(type) \ void delete_ ## type ## … Read more
Pre-ANSI C preprocessor did not allow for space between the start of a line and the “#” character; the leading “#” had to always be placed in the first column. Pre-ANSI C compilers are non-existent these days. Use which ever style (space before “#” or space between “#” and the identifier) you prefer. http://www.delorie.com/gnu/docs/gcc/cpp_48.html