[C++/STL] pointer to member function!? about …
御風只配做笨木頭
: // vc6[o] bcb4[o] g++2.91.57[o]
: #include <map>
: #include <string>
: using namespace std;
: // BCB 要求需先有 typedef. （不合理的要求）
: // VC6 和 G++ 允許直接為 map 指定 type of pointer to member function.
: class A {
: typedef bool (A::*MemFuncPtr)(char);
: map<string, MemFuncPtr> table;
: };
: int main()
: {
: }
: -- jjhou
正巧跟學弟在討論 BCB 的 __property 怎樣用 standard 的方法 implement。
我寫了下面這段 code（明天計組期中考 :~~~）：
=====================================================================
% more property.cc
#include <iostream>
#include <cstring>
using namespace std;
template <typename BASE, typename T>
class property
{
public:
typedef T (BASE::*RMemFuncPtr)();
typedef void (BASE::*WMemFuncPtr)(T&);
property () {}
property (BASE* me, RMemFuncPtr rf, WMemFuncPtr wf)
: _me(me), _rfunc(rf), _wfunc(wf) { }
// 用這個 ctor 會掛點... :<
void setup(BASE* me, RMemFuncPtr rf, WMemFuncPtr wf) {
_me = me;
_rfunc = rf;
_wfunc = wf;
}
property& operator = (T rhs) {
(_me->*_wfunc)(rhs);
return *this;
}
operator T () {
return (_me->*_rfunc)();
}
private:
BASE* _me;
RMemFuncPtr _rfunc;
WMemFuncPtr _wfunc;
};
class Test
{
public:
Test() {
Cnum.setup(this, &Test::RNum, &Test::WNum);
}
char* RNum() {
cerr << "Test::RNum called" << endl;
return const_cast<char*>(tbl[Nnum]);
}
void WNum(char* &rhs) {
cerr << "Test::WNum called" << endl;
for (int i = 0; i < 10; ++i) {
if (!strcmp(rhs, tbl[i])) {
Nnum = i;
return;
}
}
Nnum = 0;
}
property<Test, char*> Cnum;
int Nnum;
private:
static const char* tbl[10];
};
const char* Test::tbl[10] = { "零", "一", "二", "三", "四",
"五", "六", "七", "八", "九", };
int
main(int argc, char* argv[])
{
Test atext;
char buf[] = "三";
atext.Cnum = buf;
cout << atext.Cnum;
return 0;
}
% g++ -v
Reading specs from /usr/local/lib/gcc-lib/i386-portbld-freebsd3.2/egcs-2.91.66/s
p
ecs
% g++ property.cc
% ./a.out
Test::WNum called
Test::RNum called
三
%
============================================================================
若是要使用 3 個參數的 ctor 版本的話（用起來才漂亮些），Test 變成：
============================================================================
class Test
{
public:
Test() {
// Cnum.setup(this, &Test::RNum, &Test::WNum);
}
char* RNum() {
cerr << "Test::RNum called" << endl;
return const_cast<char*>(tbl[Nnum]);
}
void WNum(char* &rhs) {
cerr << "Test::WNum called" << endl;
for (int i = 0; i < 10; ++i) {
if (!strcmp(rhs, tbl[i])) {
Nnum = i;
return;
}
}
Nnum = 0;
}
property<Test, char*> Cnum(this, &Test::RNum, &Test::WNum);
int Nnum;
private:
static const char* tbl[10];
};
============================================================================
然後 g++ 跟我這樣 complain：
============================================================================
% g++ property.cc
property.cc:67: invalid use of `this' at top level
property.cc:67: incomplete type `Test' does not have member `RNum'
property.cc:67: incomplete type `Test' does not have member `WNum'
property.cc:67: warning: ANSI C++ forbids initialization of member `Cnum'
property.cc:67: warning: making `Cnum' static
property.cc:67: ANSI C++ forbids in-class initialization of non-const static member `Cnum'
property.cc:67: initializer invalid for static member with constructor
property.cc:67: (you really want to initialize it separately)
============================================================================
請問侯老或版上的各位大大，這是怎樣的一個情形啊？
又，有可能避掉 _me 嗎？
ps.電腦裡沒灌 BCB 或 VC，不知道在 BCB 或 VC 底下，
這段程式碼會變成什麼樣子... :Q
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