C++: Name Mangling

When C++ compilers compile a C++ program, it encodes all function names and

certain other identifiers to include type and scoping information. This encoding

process is called name mangling. Linker uses these mangled names to ensure

type-safe linkage. These mangled names appear in the object files and final

executable file.



What's a symbol?

In every C++ program/library/object file, all non-static functions are represented

in the binary file as symbols. These symbols are special text strings that uniquely

identify a function in the program, library or object file



The Need for Name Mangling:

C language programs does not use name mangling, because in C no two non-static

functions can have the same name. i.e., the symbol name is the same as the

function name: the symbol of myfunc will be myfunc



Because C++ allows overloading (different functions with the same name but

different number of arguments) and has many features C does not, like classes,

member functions, exception specifications — it is not possible to simply use the

function name as the symbol name. To solve that, C++ uses name mangling, which

encodes the function name and all the necessary information (like the number

and size of the arguments) into some special string which only the compiler

knows about



eg.,

bpte4500s001:/sunbuild1/giri/testcases/% nm hide.o



hide.o:



[Index]   Value      Size    Type  Bind  Other Shndx   Name

[3]     |        16|      56|FUNC |GLOB |3    |2      |__1cKCRectangleKset_values6Mii_v_

[4]     |         0|       0|NOTY |GLOB |0    |ABS    |__fsr_init_value

[1]     |         0|       0|FILE |LOCL |0    |ABS    |hide.cpp

[2]     |        88|      32|FUNC |GLOB |2    |2      |main



"__1cKCRectangleKset_values6Mii_v_" is the mangled name



But this kind of scheme is undesirable for the developers because the names

are difficult to read & debug



Two utilities are available with Sun Studio C/C++ compiler collection to convert

the mangled names to their original source code names:

1)  c++filt &

2) dem



C++filt is a filter that demangles (decodes) mangled names.

bpte4500s001% echo __1cKCRectangleKset_values6Mii_v_ | c++filt

void CRectangle::set_values(int,int)



"dem" is another utility to demangle C++ names

bpte4500s001% dem __1cKCRectangleKset_values6Mii_v_

__1cKCRectangleKset_values6Mii_v_ == void CRectangle::set_values(int,int)



Note:

C++ standard does not define how names have to be mangled; thus every compiler

mangles names in its own way. Some compilers even change their name mangling

algorithm between different versions. This could be a problem if the developers

hack & rely on how compiler mangles the C++ symbols, as the same algorithm may

not work with the next version of C++ compiler