C++ Tutorial Index

C++ Tutorial C++ History C++ Installation C++ First Program C++ cin and cout C++ Data type C++ Variable C++ operator C++ Keywords

C++ Control Statements

C++ If C++ Nested if C++ If-else C++ If-else-if C++ Switch C++ Break C++ Continue C++ Goto C++ For loop C++ While loop C++ Do while loop

C++ Functions

C++ Call by Value C++ Call by Reference C++ Recursion Function C++ Inline function C++ Friend function

C++ Arrays

Single dimension array Two dimension array

C++ Strings

C++ Strings

C++ Inheritance

C++ Inheritance Single level Inheritance Multilevel Inheritance Multiple Inheritance Hierarchical Inheritance Hybrid Inheritance

C++ Polymorphism

C++ Polymorphism C++ Overloading C++ Overriding C++ Virtual Function

C++ Pointers

C++ Pointers C++ this pointer

C++ Exception Handling

C++ Exception Handling

C++ Constructors

C++ Constructors Default Constructor Parameterize Constructor Copy constructor Constructor Overloading Destructor

C++ File Handling

C++ File Handling C++ Writing to file C++ Reading file C++ Close file

Miscellaneous

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Passing by the pointer in C++ Free vs delete() in C++ goto statement in C and C++ C++ program to read string using cin.getline() C++ String Concatenation Heap Sort in C++ Swap numbers in C++ Input Iterators in C++ Fibonacci Series in C++ C ++ Program: Alphabet Triangle and Number Triangle C++ Program: Matrix Multiplication C++ Program to Print Fibonacci Triangle Stack in C++ Maps in C++ Queue in C++ C++ Bitset C++ Algorithms Priority Queue in C++ C++ Multimap C++ Deque Function Pointer in C++ Sizeof() Operators in C++ C++ array of Pointers free() Vs delete in C Timsort Implementation Using C++ CPP Templates C++ Aggregation C++ Enumeration C++ Math Functions C++ Object Class C++ Queue Initialize Vector in C++ Vector in C++ C++ STL Components Function overloading in C++ C++ Maximum Index Problem C++ find missing in the second array C++ Program to find the product array puzzle C++ Program To Find Largest Subarray With 0 Sum C++ Program To Move All Zeros To The End Of The Array C++ Program 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Programs to Print Pyramid Patterns in C++ swap() function in C++ Structure of C++ Program Stringstream in C++ and its applications rand() and srand() in C / C++ C++ Ternary Operator C++ Scope of Variables While Loop Examples in C++ Star pattern in C++ using For Loops For Loop Examples in C++ Do-While Loop Examples in C++ Top 5 IDEs for C++ That You Should Try Once Assertions in C/C++ C++ Convert Int to String Continue in C++ While loop Diamond Pattern in C++ using For Loop How to Reverse a String in C++ using Do-While Loop How to Reverse a String in C++ using For Loop How to Reverse a String in C++ using While Loop Infinite loop in C++ Loops in C++ Returning Multiple Values from a Function using Tuple and Pair in C++ wcscpy(), wcslen(), wcscmp() Functions in C++ Auto keyword in C++ C++ 11 vs C++ 14 vs C++ 17 C++ STL (Standard Template Library) Differences Between C Structures and C++ Structures Divide by Zero Exception in C++ Dynamic Constructor in C++ Dynamic Memory Allocation in C++ Find the Size of Array in C/C++ without using sizeof() function Floating Point Operations and Associativity in C, C++ and Java Hello World Program in C++ How to create a table in C++ How to Setup Environment for C++ Programming on Mac Implementation of a Falling Matrix in C++ Message Passing in C++ Pointer to Object in C++ Templates in C++ vs Generics in Java Ways to Copy a Vector in C++ What does Buffer Flush mean in C++ sort() function in C++ Structure Sorting (By Multiple Rules) in C++ Similarities between C++ and Java std::distance in C++ Array program in C++ C++ Tricks for Competitive Programming Desired Capabilities in Selenium Web Driver in C++ Socket Programming in C++ Template Specialization in C++ Classes and Objects in C++ Convex hull Algorithm in C++ DES in C++ C++ vardiac() function Difference between Two Sets in C++ Difference between Exit and Return Structured Binding in C++ Differences between Local and Global Variable Bitwise Operator vs Logical Operator Difference between OOP and POP in C++ Fork in C++ Functors in C++ How to call a void function in C++ How to create a directory or folder in C/C++ How to create a library in C++ How to create a stack in C++ How to create the Processes with Fork in C++ How to Handle Divide by Zero Exception in C++ Lambda Expression in C++ Pattern programs in C++ Roadmap to C++ Programming Substring in C++ Virtual base class in C++ Bits stdc++.h in C++ Top 14 Best Free C++ IDE (Editor & Compiler) for Windows in 2022 Bitmasking in C++ Auto Keyword in C++ Features of OOPS in C++ Hospital Management Project in C++ How to Declare Unordered Sets in C++ How to Sort an Array in C++ Include Guards in C++ Iostream in C++ Method overriding in C++ How to run program in turbo c++ How to Use Getline in C++ Leap Year Program in C++ Naming Convention in C++ New Operator in C++ Nullptr in C++ Object Slicing in C++ Principles of Object-Oriented Programming in C++ Processing strings using std string stream in C++ Pure Virtual 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in C/C++ Depth First Search Program to Traverse a Graph in C++ Features and Use Of Pointers in C/C++ Fread Function in C++ Programming Fscanf Function in The C++ Functions in C++ With Types and Examples Gmtime Function in C/C++ How is Multiset Implemented in C++ How to Build a Program in C++ How to Declare a 2d Array Dynamically in C++ inheritance Program in C++ int Max and int Min in C/C++ is It Fine to Write Void Main Or Main in C/C++ How to create a button in C++ abs() function in C++ Compile Time Polymorphism in C++ Division in C++ Factorial of a Number in C++ using while Loop Multiset in C++ 4 Pillars of OOPs Approach in C++ Backtracking Time Complexity in C++ C++ Global Variable C++ Pipe Tutorial Observer Design Pattern in C++ Private Inheritance in C++ Pthread in C++ Parameters SDL library in C++ with Examples Pointers in C++ Abstract Factory Design Pattern in C++ Ascending order in C++ How the value is passed in C++ Call by Pointer in C++ Constexpr in C++ Deadlock in C++ Design 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How to use the string find() in C++ Dynamic Casting in C++ 2D Vector Initialization in C++ C++ GUI Visual Studio C++ IPC C++ Macro Function Example C++ Permutation Overloading Stream Insertion in C++ Overloading array Index operator in C++ Operators that cannot be overloaded in C++ Operator overloading in C++ isprint() function in c++ Is_trivial function in C++ Is assignment operator Inherited in C++ div() function in C++ Default Assignment Operator and References in C++ Copy Constructor vs Assignment Operator in C++ Conversion Operator in C++ Array sum in C++ STL C++ Define Macro C++ Design C++ Factory Pattern TCP Client Server Example in C++ Convert String to Uppercase in C++ exit() and _Exit() in C and C++ Initializer list in C++ Iterator invalidation in C++ Lower bound in C++ Modulus of Two float numbers or double number Pass by value in C++ Set insert function in C++ Std partition_point in C++ Unary Operator Overloading in C++ Using Default Arguments with Virtual Functions Virtual 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std::next and std::advance in C++ Hiding of all overloaded methods with same name in base class in C++ C++ program to concatenate two strings using operator overloading Difference between array::fill() and array::swap() in C++ Difference between Friend Function and Virtual Function in C++ Semaphores in C++ Seekg in C++

Name Mangling and extern in C++

Name Mangling and Function Overloading:

Function overloading is a feature offered by C++. As long as each function accepts various parameters, we can use this to write many functions with the same name. Function overloading cannot be understood by lower-level languages (such as C or assembly) or tools (such as linker). Each function name in these languages must be distinct for functions to be distinguishable from one another solely by name.

Functions are distinguished in C++ using both their name and parameters. For each function, a brand-new name is generated. The original C++ function's name and parameters determine the new name. It will always produce a unique name when given the name of a function and a set of parameters.

Even if the original C++ function name remains the same, if parameters (number of parameters, type of parameters, or order of parameters) change, a new name will be generated. Name mangling is the term used to describe this encoding of the function name.

The name-mangling method is compiler-dependent. Compilers can employ a variety of tactics. A name that has been distorted by one compiler might not have been distorted by other compilers.

Take into account the following Name Mangling example, which contains several f() function declarations:

// To demonstrate function overloading 
// Name Mangling
int fun(void) 
{ 
return 0; 
}
 
int fun(int) 
{ 
return 1; 
}
 
void good(void)
{ 
int i = fun(), j = fun(0); 
}

We can easily see that the above two functions, which have the same name, "fun," but the parameter is different, then the compiler will generate a new name for differentiating between the same functions, but the parameter will be the same which prevents naming conflicts and makes it possible to overload functions or variables with the same name.

The names listed above may be altered by some C++ compilers to become,

// To demonstrate function overloading 
// Name Mangling
 
int __fun_v(void) 
{ 
return 0; 
}
 
int __fun_i(int) 
{ 
return 1;
 }
 
void __good_v(void) 
{ 
int i = __fun_v(), j = __fun_i(0);
 }

Explanation:

  • In the above functions, we can easily see that compiler is generated a new name for functions which is not similar.
  • Before the compilation, Previously the 1st function name was "fun", but after the compilation, the function name is changed from "f" to "__fun_v”.
  • Similar things happen in the 2nd function and 3rd function that compiler generates the function name with the same arguments when this program is compiled.
  • So this is called Name Mangling.

Note: function overloading is not supported in C, care must be taken to ensure that no symbol names are modified while linking C code to C++.

Extern “C” in C++:

Extern "C" is a keyword in C++ that is used to indicate that the following function or variable should not be mangled. This allows C++ code to interoperate with C code, as C code does not use name mangling. When a function or variable is declared with extern "C", its name will remain the same as it would in C, making it accessible to C code.

When code is placed in the extern "C" block, the C++ compiler makes sure the function names are preserved and that the compiler emits a binary file with the names of the functions unaltered, just like a C compiler would.

In order to prevent C++ functions from being altered so that they can be called from C, the extern "C" linkage specifier can also be used.

For example, consider the following C++ code:

int add(int a, int b) 
{
    return a + b;
}

Without extern "C", the compiler would mangle the name of the function "add" to include information about its type and other attributes, such as the number and types of its parameters. This would make the function difficult or impossible for C code to call.

To prevent this, the function can be declared with extern "C" like this:

extern "C" int add(int a, int b) 
{
    return a + b;
}

This tells the compiler not to mangle the name of the function, and it will remain the same as it would in C. This makes it accessible to C code and can be called from C code without any issues.

Extern "C" is often used in header files shared between C++ and C code. For example, a C++ library might define several functions with the extern "C" in a header file, which can then be included in C code and used without any issues.

It's worth noting that extern "C" applies only to the function or variable that immediately follows it, and it's not a storage class specifier like extern, static or auto. It's also important to note that while extern "C" works for both functions and variables, not all C compilers support it.

Conclusion:

  • Since C++ allows for function overloading, extra information must be added to function names (a process known as name mangling) in order to prevent conflicts in binary code.
  • Name mangling is a technique used in C++ to encode the information about a function or variable's type, scope, and other attributes in its name, which allows the compiler to generate unique names for functions or variables that have the same name but different types or scopes.
  • Since function overloading is not supported by C, function names cannot be modified. The extern "C" block is supported by C++ to prevent linking issues. The extern "C" block's names are protected from alteration by the C++ compiler.
  • Extern "C" is a keyword in C++ that is used to indicate that the following function or variable should not be mangled, making it accessible to C code and allowing C++ code to interoperate with C code. It's a useful technique for creating libraries that can be used by both C and C++ code.