E.13. Linkage Specifications

It is possible from a C++ program to call functions written and compiled with a C compiler. As stated in Section 6.17, C++ specially encodes function names for type-safe linkage. C, however, does not encode its function names. Thus, a function compiled in C will not be recognized when an attempt is made to link C code with C++ code, because the C++ code expects a specially encoded function name. C++ enables the programmer to provide linkage specifications to inform the compiler that a function was compiled on a C compiler and to prevent the name of the function from being encoded by the C++ compiler. Linkage specifications are useful when large libraries of specialized functions have been developed, and the user either does not have access to the source code for recompilation into C++ or does not have time to convert the library functions from C to C++.

To inform the compiler that one or several functions have been compiled in C, write the function prototypes as follows:

 extern "C" function prototype // single function

 extern "C" // multiple functions
 function prototypes

These declarations inform the compiler that the specified functions are not compiled in C++, so name encoding should not be performed on the functions listed in the linkage specification. These functions can then be linked properly with the program. C++ environments normally include the standard C libraries and do not require the programmer to use linkage specifications for those functions.

Introduction to Computers, the Internet and World Wide Web

Introduction to C++ Programming

Introduction to Classes and Objects

Control Statements: Part 1

Control Statements: Part 2

Functions and an Introduction to Recursion

Arrays and Vectors

Pointers and Pointer-Based Strings

Classes: A Deeper Look, Part 1

Classes: A Deeper Look, Part 2

Operator Overloading; String and Array Objects

Object-Oriented Programming: Inheritance

Object-Oriented Programming: Polymorphism


Stream Input/Output

Exception Handling

File Processing

Class string and String Stream Processing

Web Programming

Searching and Sorting

Data Structures

Bits, Characters, C-Strings and structs

Standard Template Library (STL)

Other Topics

Appendix A. Operator Precedence and Associativity Chart

Appendix B. ASCII Character Set

Appendix C. Fundamental Types

Appendix D. Number Systems

Appendix E. C Legacy Code Topics

Appendix F. Preprocessor

Appendix G. ATM Case Study Code

Appendix H. UML 2: Additional Diagram Types

Appendix I. C++ Internet and Web Resources

Appendix J. Introduction to XHTML

Appendix K. XHTML Special Characters

Appendix L. Using the Visual Studio .NET Debugger

Appendix M. Using the GNU C++ Debugger


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C++ How to Program
C++ How to Program (5th Edition)
ISBN: 0131857576
EAN: 2147483647
Year: 2004
Pages: 627
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