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In the C++ programming language, a reference is a simple reference datatype that is less powerful but safer than the pointer type inherited from C.The name C++ reference may cause confusion, as in computer science a reference is a general concept datatype, with pointers and C++ references being specific reference datatype implementations.
However, C is not a subset of C++, [3] and nontrivial C programs will not compile as C++ code without modification. Likewise, C++ introduces many features that are not available in C and in practice almost all code written in C++ is not conforming C code. This article, however, focuses on differences that cause conforming C code to be ill ...
The details differ between C (where only objects and functions - but not types - have linkage) and C++ and between this simplified overview. Linkage between languages must be done with some care, as different languages adorn their external symbols differently. A common idiom uses extern "C" to link C++ and C code.
When the program calls the speak function on a Cat reference (which can refer to an instance of Cat, or an instance of HouseCat or Lion), the code must be able to determine which implementation of the function the call should be dispatched to. This depends on the actual class of the object, not the class of the reference to it (Cat).
For example, symbol table entries representing initialized data are denoted by the character "d" and symbol table entries for functions have the symbol type "t" (because executable code is located in the text section of an object file). Additionally, the capitalization of the symbol type indicates the type of linkage: lower-case letters ...
In some programming language environments (at least one proprietary Lisp implementation, for example), [citation needed] the value used as the null pointer (called nil in Lisp) may actually be a pointer to a block of internal data useful to the implementation (but not explicitly reachable from user programs), thus allowing the same register to be used as a useful constant and a quick way of ...
For example, a binary is dynamically linked against libraries libfoo.so and libbar.so. libfoo defines symbol f and declares it as weak. libbar also defines f and declares it as strong. Depending on the library ordering on the link command line (i.e. -lfoo -lbar ) the dynamic linker uses the weak f from libfoo.so although a strong version is ...
Or there must be a declaration of the variable, with the keyword extern, inside the function. The static keyword (static and extern are mutually exclusive), applied to the definition of an external variable, changes this a bit: the variable can only be accessed by the functions in the same module where it was defined. But it is possible for a ...