How does an extern “C” declaration work?

Question

I\'m taking a programming languages course and we\'re talking about the extern \"C\" declaration.

How does this declaration work at a deeper level othe

Answer 1

extern "C", is a keyword to declare a function with C bindings, because C compiler and C++ compiler will translate source into different form in object file:

For example, a code snippet is as follows:

int _cdecl func1(void) {return 0}
int _stdcall func2(int) {return 0}
int _fastcall func3(void) {return 1}

32-bit C compilers will translate the code in the form as follows:

_func1
_func2@4
@func3@4

in the cdecl, func1 will translate as '_name'

in the stdcall, func2 will translate as '_name@X'

in the fastcall, func2 will translate as '@name@X'

'X' means the how many bytes of the parameters in parameter list.

64-bit convention on Windows has no leading underscore

In C++, classes, templates, namespaces and operator overloading are introduced, since it is not allowed two functions with the same name, C++ compiler provide the type information in the symbol name,

for example, a code snippet is as follows:

int func(void) {return 1;}
int func(int) {return 0;}
int func_call(void) {int m=func(), n=func(0);}

C++ compiler will translate the code as follows:

int func_v(void) {return 1;}
int func_i(int) {return 0;}
int func_call(void) {int m=_func_v(), n=_func_i(0);}

'_v' and '_i' are type information of 'void' and 'int'