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An external variable can be accessed by all the functions in all the modules of a program. It is a global variable.For a function to be able to use the variable, a declaration or the definition of the external variable must lie before the function definition in the source code.
The minimum of code needed to compile for C++ is a function, for Java is a class. C++ allows a range of implicit conversions between native types (including some narrowing conversions), and also allows defining implicit conversions involving user-defined types.
This is also valid in C++. (C++ 98/03 deprecated this usage in favor of anonymous namespaces, but is no longer deprecated in C++ 11.) Also, C++ implicitly treats any const namespace-scope variable as having internal linkage unless it is explicitly declared extern, unlike C. A name's linkage is related to, but distinct from, its scope. The scope ...
Likewise, for C code to call a C++ function bar(), the C++ code for bar() must be declared with extern "C". A common practice for header files to maintain both C and C++ compatibility is to make its declaration be extern "C" for the scope of the header: [21]
Information hiding is accomplished by furnishing a compiled version of the source code that is interfaced via a header file. Almost always, there is a way to override such protection – usually via reflection API (Ruby, Java, C#, etc.), sometimes by mechanism like name mangling , or special keyword usage like friend in C++.
[8] [9] Common Lisp; Compiled Native Interface (CNI), alternative to JNI used in the GNU compiler environment. One of the bases of the Component Object Model is a common interface format, which natively uses the same types as Visual Basic for strings and arrays. D does it the same way as C++ does, with extern "C" through extern (C++)
32-bit compilers emit, respectively: _f _g@4 @h@4 In the stdcall and fastcall mangling schemes, the function is encoded as _name@X and @name@X respectively, where X is the number of bytes, in decimal, of the argument(s) in the parameter list (including those passed in registers, for fastcall).
In any translation unit, a template, type, function, or object can have no more than one definition. Some of these can have any number of declarations. A definition provides an instance. In the entire program, an object or non-inline function cannot have more than one definition; if an object or function is used, it must have exactly one ...