========= case 1 =========

both fun1() fun2() called in main() have default parameters
------test71.cpp-------
#include <stdio.h>

int fun1(int x=10);

int fun1(int x)
{
    printf("fun1() x=%d\n");
    return 0;
}

int fun2(int x);

int fun2(int x=10)
{
    printf("fun2() x=%d\n");
    return 0;
}

// cl /Fatest71.asm test71.cpp

void main()
{
    fun1();
    fun2();
}
-------test71.asm---------
	TITLE	test71.cpp
	.386P
include listing.inc
if @Version gt 510
.model FLAT
else
_TEXT	SEGMENT PARA USE32 PUBLIC 'CODE'
_TEXT	ENDS
_DATA	SEGMENT DWORD USE32 PUBLIC 'DATA'
_DATA	ENDS
CONST	SEGMENT DWORD USE32 PUBLIC 'CONST'
CONST	ENDS
_BSS	SEGMENT DWORD USE32 PUBLIC 'BSS'
_BSS	ENDS
_TLS	SEGMENT DWORD USE32 PUBLIC 'TLS'
_TLS	ENDS
FLAT	GROUP _DATA, CONST, _BSS
	ASSUME	CS: FLAT, DS: FLAT, SS: FLAT
endif
PUBLIC	?fun1@@YAHH@Z					; fun1
EXTRN	_printf:NEAR
_DATA	SEGMENT
$SG580	DB	'fun1() x=%d', 0aH, 00H
_DATA	ENDS
_TEXT	SEGMENT
?fun1@@YAHH@Z PROC NEAR					; fun1
; File test71.cpp
; Line 8
	push	ebp
	mov	ebp, esp
; Line 9
	push	OFFSET FLAT:$SG580
	call	_printf
	add	esp, 4
; Line 10
	xor	eax, eax
; Line 11
	pop	ebp
	ret	0
?fun1@@YAHH@Z ENDP					; fun1
_TEXT	ENDS
PUBLIC	?fun2@@YAHH@Z					; fun2
_DATA	SEGMENT
	ORG $+3
$SG586	DB	'fun2() x=%d', 0aH, 00H
_DATA	ENDS
_TEXT	SEGMENT
?fun2@@YAHH@Z PROC NEAR					; fun2
; Line 16
	push	ebp
	mov	ebp, esp
; Line 17
	push	OFFSET FLAT:$SG586
	call	_printf
	add	esp, 4
; Line 18
	xor	eax, eax
; Line 19
	pop	ebp
	ret	0
?fun2@@YAHH@Z ENDP					; fun2
_TEXT	ENDS
PUBLIC	_main
_TEXT	SEGMENT
_main	PROC NEAR
; Line 22
	push	ebp
	mov	ebp, esp
; Line 23
	push	10					; 0000000aH
	call	?fun1@@YAHH@Z				; fun1
	add	esp, 4
; Line 24
	push	10					; 0000000aH
	call	?fun2@@YAHH@Z				; fun2
	add	esp, 4
; Line 25
	pop	ebp
	ret	0
_main	ENDP
_TEXT	ENDS
END

========= case 2 =========

fun1() called in main() has default parameters
fun2() called in main() does not have default parameter
------test71.cpp--------
// cl /Fatest71.asm test71.cpp

#include "test71a.h"

void main()
{
    fun1();
    fun2(); // error: function does not take zero parameter
}
------test71a.h--------
int fun1(int x=10);

int fun2(int x);
------test71a.cpp--------
#include <stdio.h>

int fun1(int x)
{
    printf("fun1() x=%d\n");
    return 0;
}

int fun2(int x=10)
{
    printf("fun2() x=%d\n");
    return 0;
}