C

Although name mangling is not generally required or used by languages that do not support function overloading, like C and classic Pascal, they use it in some cases to provide added information about a function. For example, compilers targeted at Microsoft Windows platforms support a variety of calling conventions, which determine the manner in which parameters are sent to subroutines and results are returned. Because the different calling conventions are incompatible with one another, compilers mangle symbols with codes detailing which convention should be used to call the specific routine.

The mangling scheme for Windows was established by Microsoft and has been informally followed by other compilers including Digital Mars, Borland, and GNU Compiler Collection (GCC) when compiling code for the Windows platforms. The scheme even applies to other languages, such as Pascal, D, Delphi, Fortran, and C#. This allows subroutines written in those languages to call, or be called by, extant Windows libraries using a calling convention different from their default.

When compiling the following C examples:

int _cdecl    f (int x) { return 0; }
int _stdcall  g (int y) { return 0; }
int _fastcall h (int z) { return 0; }

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 the case of cdecl, the function name is merely prefixed by an underscore.

The 64-bit convention on Windows (Microsoft C) has no leading underscore. This difference may in some rare cases lead to unresolved externals when porting such code to 64 bits. For example, Fortran code can use 'alias' to link against a C method by name as follows:

SUBROUTINE f()
!DEC$ ATTRIBUTES C, ALIAS:'_f' :: f
END SUBROUTINE

This will compile and link fine under 32 bits, but generate an unresolved external _f under 64 bits. One workaround for this is not to use 'alias' at all (in which the method names typically need to be capitalized in C and Fortran). Another is to use the BIND option:

SUBROUTINE f() BIND(C,NAME="f")
END SUBROUTINE

In C, most compilers also mangle static functions and variables (and in C++ functions and variables declared static or put in the anonymous namespace) in translation units using the same mangling rules as for their non-static versions. If functions with the same name (and parameters for C++) are also defined and used in different translation units, it will also mangle to the same name, potentially leading to a clash. However, they will not be equivalent if they are called in their respective translation units. Compilers are usually free to emit arbitrary mangling for these functions, because it is illegal to access these from other translation units directly, so they will never need linking between different object code (linking of them is never needed). To prevent linking conflicts, compilers will use standard mangling, but will use so-called 'local' symbols. When linking many such translation units there might be multiple definitions of a function with the same name, but resulting code will only call one or another depending on which translation unit it came from. This is usually done using the relocation mechanism.

C++

C++ compilers are the most widespread users of name mangling. The first C++ compilers were implemented as translators to C source code, which would then be compiled by a C compiler to object code; because of this, symbol names had to conform to C identifier rules. Even later, with the emergence of compilers that produced machine code or assembly directly, the system's linker generally did not support C++ symbols, and mangling was still required.

The C++ language does not define a standard decoration scheme, so each compiler uses its own. C++ also has complex language features, such as classes, templates, namespaces, and operator overloading, that alter the meaning of specific symbols based on context or usage. Meta-data about these features can be disambiguated by mangling (decorating) the name of a symbol. Because the name-mangling systems for such features are not standardized across compilers, few linkers can link object code that was produced by different compilers.

int  f () { return 1; }
int  f (int)  { return 0; }
void g () { int i = f(), j = f(0); }

int  __f_v () { return 1; }
int  __f_i (int)  { return 0; } 
void __g_v () { int i = __f_v(), j = __f_i(0); }

namespace wikipedia 
{
   class article 
   {
   public:
      std::string format ();  // = _ZN9wikipedia7article6formatEv

      bool print_to (std::ostream&);  // = _ZN9wikipedia7article8print_toERSo

      class wikilink 
      {
      public:
         wikilink (std::string const& name);  // = _ZN9wikipedia7article8wikilinkC1ERKSs
      };
   };
}

_ZN9wikipedia7article6formatE

_ZN9wikipedia7article6formatEv

_ZN9wikipedia7article8print_toERSo

#ifdef __cplusplus 
extern "C" {
#endif
    /* ... */
#ifdef __cplusplus
}
#endif

#ifdef __cplusplus
extern "C" {
#endif

void *memset (void *, int, size_t);
char *strcat (char *, const char *);
int   strcmp (const char *, const char *);
char *strcpy (char *, const char *);

#ifdef __cplusplus
}
#endif

if (strcmp(argv[1], "-x") == 0) 
    strcpy(a, argv[2]);
else 
    memset (a, 0, sizeof(a));

if (__1cGstrcmp6Fpkc1_i_(argv[1], "-x") == 0) 
    __1cGstrcpy6Fpcpkc_0_(a, argv[2]);
else 
    __1cGmemset6FpviI_0_ (a, 0, sizeof(a));

$ c++filt -n _ZNK3MapI10StringName3RefI8GDScriptE10ComparatorIS0_E16DefaultAllocatorE3hasERKS0_
Map<StringName, Ref<GDScript>, Comparator<StringName>, DefaultAllocator>::has(StringName const&) const

#include <stdio.h>
#include <stdlib.h>
#include <cxxabi.h>

int main() {
	const char *mangled_name = "_ZNK3MapI10StringName3RefI8GDScriptE10ComparatorIS0_E16DefaultAllocatorE3hasERKS0_";
	int status = -1;
	char *demangled_name = abi::__cxa_demangle(mangled_name, NULL, NULL, &status);
	printf("Demangled: %s\n", demangled_name);
	free(demangled_name);
	return 0;
}

Demangled: Map<StringName, Ref<GDScript>, Comparator<StringName>, DefaultAllocator>::has(StringName const&) const

Java

In Java, the signature of a method or a class contains its name and the types of its method arguments and return value, where applicable. The format of signatures is documented, as the language, compiler, and .class file format were all designed together (and had object-orientation and universal interoperability in mind from the start).

public class foo {
    class bar {
        public int x;
    }

    public void zark () {
        Object f = new Object () {
            public String toString() {
                return "hello";
            }
        };
    }
}

Python

In Python, mangling is used for class attributes that one does not want subclasses to use^[8] which are designated as such by giving them a name with two or more leading underscores and no more than one trailing underscore. For example, __thing will be mangled, as will ___thing and __thing_, but __thing__ and __thing___ will not. Python's runtime does not restrict access to such attributes, the mangling only prevents name collisions if a derived class defines an attribute with the same name.

On encountering name mangled attributes, Python transforms these names by prepending a single underscore and the name of the enclosing class, for example:

>>> class Test:
...     def __mangled_name(self):
...         pass
...     def normal_name(self):
...         pass
>>> t = Test()
>>> [attr for attr in dir(t) if "name" in attr]
['_Test__mangled_name', 'normal_name']

Pascal

exports
  myFunc name 'myFunc',
  myProc name 'myProc';

Fortran

Name mangling is also necessary in Fortran compilers, originally because the language is case insensitive. Further mangling requirements were imposed later in the evolution of the language because of the addition of modules and other features in the Fortran 90 standard. The case mangling, especially, is a common issue that must be dealt with to call Fortran libraries, such as LAPACK, from other languages, such as C.

Because of the case insensitivity, the name of a subroutine or function FOO must be converted to a standardized case and format by the compiler so that it will be linked in the same way regardless of case. Different compilers have implemented this in various ways, and no standardization has occurred. The AIX and HP-UX Fortran compilers convert all identifiers to lower case foo, while the Cray and Unicos Fortran compilers converted identifiers to all upper case FOO. The GNU g77 compiler converts identifiers to lower case plus an underscore foo_, except that identifiers already containing an underscore FOO_BAR have two underscores appended foo_bar__, following a convention established by f2c. Many other compilers, including Silicon Graphics's (SGI) IRIX compilers, GNU Fortran, and Intel's Fortran compiler (except on Microsoft Windows), convert all identifiers to lower case plus an underscore (foo_ and foo_bar_, respectively). On Microsoft Windows, the Intel Fortran compiler defaults to uppercase without an underscore.^[9]

Identifiers in Fortran 90 modules must be further mangled, because the same procedure name may occur in different modules. Since the Fortran 2003 Standard requires that module procedure names not conflict with other external symbols,^[10] compilers tend to use the module name and the procedure name, with a distinct marker in between. For example:

module m 
contains
   integer function five()
      five = 5
   end function five
end module m

In this module, the name of the function will be mangled as __m_MOD_five (e.g., GNU Fortran), m_MP_five_ (e.g., Intel's ifort), m.five_ (e.g., Oracle's sun95), etc. Since Fortran does not allow overloading the name of a procedure, but uses generic interface blocks and generic type-bound procedures instead, the mangled names do not need to incorporate clues about the arguments.

The Fortran 2003 BIND option overrides any name mangling done by the compiler, as shown above.

Rust

Function names are mangled by default in Rust. However, this can be disabled by the #[no_mangle] function attribute. This attribute can be used to export functions to C, C++, or Objective-C.^[11] Further, along with the #[start] function attribute or the #[no_main] crate attribute, it allows the user to define a C-style entry point for the program.^[12]

Rust has used many versions of symbol mangling schemes that can be selected at compile time with an -Z symbol-mangling-version option. The following manglers are defined:

• legacy A C++ style mangling based on the Itanium IA-64 C++ ABI. Symbols begin with _ZN, and filename hashes are used for disambiguation. Used since Rust 1.9.^[13]
• v0 An improved version of the legacy scheme, with changes for Rust. Symbols begin with _R. Polymorphism can be encoded. Functions don't have return types encoded (Rust does not have overloading). Unicode names use modified punycode. Compression (backreference) use byte-based addressing. Used since Rust 1.37.^[14]

Examples are provided in the Rust symbol-names tests.^[15]

Objective-C

Essentially two forms of method exist in Objective-C, the class ("static") method, and the instance method. A method declaration in Objective-C is of the following form:

+ (return-type) name0:parameter0 name1:parameter1 ...
– (return-type) name0:parameter0 name1:parameter1 ...

Class methods are signified by +, instance methods use -. A typical class method declaration may then look like:

+ (id) initWithX: (int) number andY: (int) number;
+ (id) new;

With instance methods looking like this:

- (id) value;
- (id) setValue: (id) new_value;

Each of these method declarations have a specific internal representation. When compiled, each method is named according to the following scheme for class methods:

_c_Class_name0_name1_ ...

and this for instance methods:

_i_Class_name0_name1_ ...

The colons in the Objective-C syntax are translated to underscores. So, the Objective-C class method + (id) initWithX: (int) number andY: (int) number;, if belonging to the Point class would translate as _c_Point_initWithX_andY_, and the instance method (belonging to the same class) - (id) value; would translate to _i_Point_value.

Each of the methods of a class are labeled in this way. However, to look up a method that a class may respond to would be tedious if all methods are represented in this fashion. Each of the methods is assigned a unique symbol (such as an integer). Such a symbol is known as a selector. In Objective-C, one can manage selectors directly – they have a specific type in Objective-C – SEL.

During compiling, a table is built that maps the textual representation, such as _i_Point_value, to selectors (which are given a type SEL). Managing selectors is more efficient than manipulating the text representation of a method. Note that a selector only matches a method's name, not the class it belongs to: different classes can have different implementations of a method with the same name. Because of this, implementations of a method are given a specific identifier too, these are known as implementation pointers, and are also given a type, IMP.

Message sends are encoded by the compiler as calls to the id objc_msgSend (id receiver, SEL selector, ...) function, or one of its cousins, where receiver is the receiver of the message, and SEL determines the method to call. Each class has its own table that maps selectors to their implementations – the implementation pointer specifies where in memory the implementation of the method resides. There are separate tables for class and instance methods. Apart from being stored in the SEL to IMP lookup tables, the functions are essentially anonymous.

The SEL value for a selector does not vary between classes. This enables polymorphism.

The Objective-C runtime maintains information about the argument and return types of methods. However, this information is not part of the name of the method, and can vary from class to class.

Since Objective-C does not support namespaces, there is no need for the mangling of class names (that do appear as symbols in generated binaries).

Swift

Swift keeps metadata about functions (and more) in the mangled symbols referring to them. This metadata includes the function's name, attributes, module name, parameter types, return type, and more. For example:

The mangled name for a method func calculate(x: int) -> int of a MyClass class in module test is _TFC4test7MyClass9calculatefS0_FT1xSi_Si, for 2014 Swift. The components and their meanings are as follows:^[16]

• _T: The prefix for all Swift symbols. Everything will start with this.
• F: Non-curried function.
• C: Function of a class, i.e. a method
• 4test: Module name, prefixed with its length.
• 7MyClass: Name of class the function belongs to, prefixed with its length.
• 9calculate: Function name, prefixed with its length.
• f: The function attribute. In this case ‘f’, which means a normal function.
• S0: Designates the type of the first parameter (namely the class instance) as the first in the type stack (here MyClass is not nested and thus has index 0).
• _FT: This begins the type list for the parameter tuple of the function.
• 1x: External name of first parameter of the function.
• Si: Indicates builtin Swift type Swift.Int for the first parameter.
• _Si: The return type: again Swift.Int.

Mangling for versions since Swift 4.0 is documented officially. It retains some similarity to Itanium.^[17]