c++ - Calling a function pointer whose assigned function has less arguments then the pointer type -

consider following code:

#include <iostream>  typedef int (*test_func_t) (int, int, int);  int print_integer (int a) {     std::cout << "num: " << << "\n";     return a; }  int main (int argc, char * argv[]) {     test_func_t func = (test_func_t) &print_integer;     std::cout << "calling 3 parameters func(5,7,9)\n";     func(5,7,9);     return 0; } 

as can see, type (test_func_t) defined function 3 int arguments. function pointer (func) assigned pointer "print_integer", receives 1 argument, , function pointer called 3 arguments (5, 7, 9).

this code works , produces "num: 5" output.

gdb disas output (intel syntax)

disas main ...    0x080486cb <+9>:     mov    dword ptr [esp+0x1c],0x804867d ...    0x080486e0 <+37>:    mov    dword ptr [esp+0x8],0x9    0x080486e8 <+45>:    mov    dword ptr [esp+0x4],0x7    0x080486f0 <+53>:    mov    dword ptr [esp],0x5    0x080486f7 <+60>:    mov    eax,dword ptr [esp+0x1c]    0x080486fb <+64>:    call   eax  disas print_integer    ...    0x08048683 <+6>:     mov    dword ptr [esp+0x4],0x8048830    0x0804868b <+14>:    mov    dword ptr [esp],0x8049ae0    0x08048692 <+21>:    call   0x8048530 <std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*)@plt>    0x08048697 <+26>:    mov    edx,dword ptr [ebp+0x8]    0x0804869a <+29>:    mov    dword ptr [esp+0x4],edx    0x0804869e <+33>:    mov    dword ptr [esp],eax    0x080486a1 <+36>:    call   0x80484d0 <std::ostream::operator<<(int)@plt> 

as can see, rest of arguments ([ebp+0x12] , [ebp+0x16]) not used.

my questions:

1. this seems work on linux x86 __cdecl calling convention. safe on other architectures , calling conventions well?
2. does c/c++ standard allows/defines result of assigning function pointer function expects fewer arguments?

example of such use: node.js's node_module registers function type has 3 arguments [exports, module, priv]. called 3 formal examples show registering of function 1 or 2 arguments.

quoting c++11 standard expr.reinterpret.cast 6:

a function pointer can explicitly converted function pointer of different type. effect of calling function through pointer function type (8.3.5) is not same type used in definition of function undefined.

so, i'd not safe in general. undefined behaviour. said, don't know how other implementation of c++ behave in situation.