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What exactly does One Definition Rule in C++ say? The only trustworthy occurence I can find is in The C++ Programming Language, 3rd. ed., P. 9.2.3. Is there any official definition of the rule except that?
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10. +1 for the succinct opening sentence: "In plain word, odr-used means something(variable or function) is used in a context where the definition of it must be present."
If an object, a reference or a function is odr-used, its definition must exist somewhere in the program; a violation of that is usually a link-time error. struct S { static const int x = 0; // static data member // a definition outside of class is required if it is odr-used }; const int& f(const int& r); int n = b ? (
The #define creates a macro, which is the association of an identifier or parameterized identifier with a token string. After the macro is defined, the compiler can substitute the token string for each occurrence of the identifier in the source file.
Inline function in C++ is an enhancement feature that improves the execution time and speed of the program. The main advantage of inline functions is that you can use them with C++ classes as well.
The truth is in the standard (3.2 One definition rule) :
No translation unit shall contain more than one definition of any variable, function, class type, enumeration type or template.
[...]
Every program shall contain exactly one definition of every non-inline function or object that is used in that program; no diagnostic required. The definition can appear explicitly in the program, it can be found in the standard or a user-defined library, or (when appropriate) it is implicitly defined (see 12.1, 12.4 and 12.8). An inline function shall be defined in every translation unit in which it is used.
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