static const vs #define

Is it better to use static const vars than #define preprocessor? Or maybe it depends on the context?

What are advantages/disadvantages for each method?

“static const” vs “#define” in C

Which one is better to use among the below statements in C? static const int var=5; or #define var 5

Const vs Static Const

How does the compiler (e.g. GCC) allocates const and static const variable, as in, where would it reside? In data memory or program memory?

How to define static const member?

My Test class has a const static member of a subtype. I usually define this const static member as follows. class Test { public: class Dummy {}; private: static Dummy const dummy; }; Test::Dummy const

define() vs const

Pretty straightforward question: In PHP, when do you use define(‘FOO’, 1); and when do you use const FOO = 1; What are the main differences between those two?

static const Vs extern const

I have been using static const in my header files as so: static NSString * const myString = @foo; But have read that this is not the ‘safe’ or correct wary of doing this. Apparently if i want my co

Difference between static const and #define in Objective-C [duplicate]

Possible Duplicate: “static const” vs “#define” in C In Objective-C what is the difference between the following two lines: #define myInteger 5 static const NSInteger myInteger = 5; Assume they’re

const string vs. #define

i need to share some strings in my c++ program. should i use #define or const string? thanks mystring1.h #define str1 str1 #define str2 str2 Or mystring2.h extern const string str1; extern cons

#define MY_INT VS const int MY_INT [duplicate]

Possible Duplicate: “static const” vs “#define” in c When I do this : #define WEEKDAYS 7 and that : const int WEEKDAYS = 7; Any difference between them ? seems that both do the same thing – sets

static constant Vs define directive

I want to define a constant in my .m file. I can see two options here: static NSString *const kMyLabel = @myLabel; #define kMyLabel @myLabel Which one is the best? Is there any issues with using

const string vs static string in c#

Is using static string better than const string in C# static string _mystr; vs const string Mystr;


Using a static const is like using any other const variables in your code. This means you can trace wherever the information comes from, as opposed to a #define that will simply be replaced in the code in the pre-compilation process.

You might want to take a look at the C++ FAQ Lite for this question:

Please see here: static const vs define

usually a const declaration (notice it doesn’t need to be static) is the way to go

Personally, I loathe the preprocessor, so I’d always go with const.

The main advantage to a #define is that it requires no memory to store in your program, as it is really just replacing some text with a literal value. It also has the advantage that it has no type, so it can be used for any integer value without generating warnings.

Advantages of “const”s are that they can be scoped, and they can be used in situations where a pointer to an object needs to be passed.

I don’t know exactly what you are getting at with the “static” part though. If you are declaring globally, I’d put it in an anonomous namespace instead of using static. For example

namespace {
   unsigned const seconds_per_minute = 60;

int main (int argc; char *argv[]) {

If this is a C++ question and it mentions #define as an alternative, then it is about “global” (i.e. file-scope) constants, not about class members. When it comes to such constants in C++ static const is redundant. In C++ const have internal linkage by default and there’s no point in declaring them static. So it is really about const vs. #define.

And, finally, in C++ const is preferable. At least because such constants are typed and scoped. There are simply no reasons to prefer #define over const, aside from few exceptions.

String constants, BTW, are one example of such an exception. With #defined string constants one can use compile-time concatenation feature of C/C++ compilers, as in

#define OUT_NAME "output"
#define LOG_EXT ".log"
#define TEXT_EXT ".txt"

const char *const log_file_name = OUT_NAME LOG_EXT;
const char *const text_file_name = OUT_NAME TEXT_EXT;

P.S. Again, just in case, when someone mentions static const as an alternative to #define, it usually means that they are talking about C, not about C++. I wonder whether this question is tagged properly…

  • A static const is typed (it has a type) and can be checked by the compiler for validity, redefinition etc.
  • a #define can be redifined undefined whatever.

Usually you should prefer static consts. It has no disadvantage. The prprocessor should mainly be used for conditional compilation (and sometimes for really dirty trics maybe).

Pros and cons to everything, depending on usage:

  • enums
    • only possible for integer values
    • properly scoped / identifier clash issues handled nicely, particularly in C++11 enum classes where the enumerations for enum class X are disambiguated by the scope X::
    • strongly typed, but to a big-enough signed-or-unsigned int size over which you have no control in C++03 (though you can specify a bit field into which they should be packed if the enum is a member of struct/class/union), while C++11 defaults to int but can be explicitly set by the programmer
    • can’t take the address – there isn’t one as the enumeration values are effectively substituted inline at the points of usage
    • stronger usage restraints (e.g. incrementing – template <typename T> void f(T t) { cout << ++t; } won’t compile, though you can wrap an enum into a class with implicit constructor, casting operator and user-defined operators)
    • each constant’s type taken from the enclosing enum, so template <typename T> void f(T) get a distinct instantiation when passed the same numeric value from different enums, all of which are distinct from any actual f(int) instantiation. Each function’s object code could be identical (ignoring address offsets), but I wouldn’t expect a compiler/linker to eliminate the unnecessary copies, though you could check your compiler/linker if you care.
    • even with typeof/decltype, can’t expect numeric_limits to provide useful insight into the set of meaningful values and combinations (indeed, “legal” combinations aren’t even notated in the source code, consider enum { A = 1, B = 2 } – is A|B “legal” from a program logic perspective?)
    • the enum’s typename may appear in various places in RTTI, compiler messages etc. – possibly useful, possibly obfuscation
    • you can’t use an enumeration without the translation unit actually seeing the value, which means enums in library APIs need the values exposed in the header, and make and other timestamp-based recompilation tools will trigger client recompilation when they’re changed (bad!)
  • consts
    • properly scoped / identifier clash issues handled nicely
    • strong, single, user-specified type
      • you might try to “type” a #define ala #define S std::string(“abc”), but the constant avoids repeated construction of distinct temporaries at each point of use
    • One Definition Rule complications
    • can take address, create const references to them etc.
    • most similar to a non-const value, which minimises work and impact if switching between the two
    • value can be placed inside the implementation file, allowing a localised recompile and just client links to pick up the change
  • defines
    • “global” scope / more prone to conflicting usages, which can produce hard-to-resolve compilation issues and unexpected run-time results rather than sane error messages; mitigating this requires:
      • long, obscure and/or centrally coordinated identifiers, and access to them can’t benefit from implicitly matching used/current/Koenig-looked-up namespace, namespace aliases etc.
      • while the trumping best-practice allows template parameter identifiers to be single-character uppercase letters (possibly followed by a number), other use of identifiers without lowercase letters is conventionally reserved for and expected of preprocessor defines (outside the OS and C/C++ library headers). This is important for enterprise scale preprocessor usage to remain manageable. 3rd party libraries can be expected to comply. Observing this implies migration of existing consts or enums to/from defines involves a change in capitalisation, and hence requires edits to client source code rather than a “simple” recompile. (Personally, I capitalise the first letter of enumerations but not consts, so I’d be hit migrating between those two too – maybe time to rethink that.)
    • more compile-time operations possible: string literal concatenation, stringification (taking size thereof), concatenation into identifiers
      • downside is that given #define X “x” and some client usage ala “pre” X “post”, if you want or need to make X a runtime-changeable variable rather than a constant you force edits to client code (rather than just recompilation), whereas that transition is easier from a const char* or const std::string given they already force the user to incorporate concatenation operations (e.g. “pre” + X + “post” for string)
    • can’t use sizeof directly on a defined numeric literal
    • untyped (GCC doesn’t warn if compared to unsigned)
    • some compiler/linker/debugger chains may not present the identifier, so you’ll be reduced to looking at “magic numbers” (strings, whatever…)
    • can’t take the address
    • the substituted value need not be legal (or discrete) in the context where the #define is created, as it’s evaluated at each point of use, so you can reference not-yet-declared objects, depend on “implementation” that needn’t be pre-included, create “constants” such as { 1, 2 } that can be used to initialise arrays, or #define MICROSECONDS *1E-6 etc. (definitely not recommending this!)
    • some special things like __FILE__ and __LINE__ can be incorporated into the macro substitution
    • you can test for existence and value in #if statements for conditionally including code (more powerful than a post-preprocessing “if” as the code need not be compilable if not selected by the preprocessor), use #undef-ine, redefine etc.
    • substituted text has to be exposed:
      • in the translation unit it’s used by, which means macros in libraries for client use must be in the header, so make and other timestamp-based recompilation tools will trigger client recompilation when they’re changed (bad!)
      • or on the command line, where even more care is needed to make sure client code is recompiled (e.g. the Makefile or script supplying the definition should be listed as a dependency)

As a general rule, I use consts and consider them the most professional option for general usage (though the others have a simplicity appealing to this old lazy programmer).

Defining constants by using preprocessor directive #define is not recommended to apply not only in C++, but also in C. These constants will not have the type. Even in C was proposed to use const for constants.

If you are defining a constant to be shared among all the instances of the class, use static const. If the constant is specific to each instance, just use const (but note that all constructors of the class must initialize this const member variable in the initialization list).