1.類定義輸入運算符 >> 時候，代碼最后應(yīng)該檢測 輸入流是否為有效，如果無效，應(yīng)該把輸入對象置于默認(rèn)初始化狀態(tài)。

??? 定義>>時候，類必須是非常量引用。定義<<，最好是常量引用。

???? 定義的時候不能加friend.

2.關(guān)于日期輸入的正確格式：

Date & Date::operator=(const string &date) { istringstream is(date); char ch1,ch2; is >> year >> ch1 >> month >> ch2 >> day; if(!is || ch1 != '-' || ch2 != '-' )throw invalid_argument("Bad date"); if(month < 1 || month > 12 || day < 1 || day > 21)throw invalid_argument("Bad date"); return *this; }

3.

#include <string> #include <iostream> using namespace std; class Test {int &fun()const{return a;}private:int a;}; int main() { Test t1;return 0; }

binding reference of type ‘int&’ to ‘const int’ discards qualifiers

const成員函數(shù)不能返回類成員的非常量引用。因為有修改類成員的風(fēng)險。

3.

g++報錯"undefined reference to `vtable for XXX' "的原因 原因就一個:沒有全部實現(xiàn)XXX基類的純虛函數(shù).

4.

// items定義成一個multiset，可以將同一本書的多條交易信息保存到一個multiset中,
// 這里不能用圓括號，因為default member initializer來初始化成員有2
// 個方法，list initialization,即一對花括號.第二種是copy initializa//tion，即 等號.如果嘗試用圓括號，編譯器會誤以為是函數(shù)聲明，所以/報告compare is not a type..
?? ??? ?multiset<shared_ptr<Quote>,decltype(compare)*> items{compare};

所以這里給items初始化有不能使用圓括號。

5.

MoveBase_cmd_vel_sub = node_handle.subscribe( "/movebase_cmd_vel", 60, DHRobotBase::moveBase_cmd_vel); // 訂閱 topic

在使用這句話時出現(xiàn)這個問題：

?error: invalid use of non-static member function? ? ? ?"/movebase_cmd_vel", 60, DHRobotBase::moveBase_cmd_vel);

折騰了好久終于弄好了:

MoveBase_cmd_vel_sub = node_handle.subscribe("/movebase_cmd_vel", 60, &DHRobotBase::moveBase_cmd_vel,this); // 訂閱topic

原因大概是這個：在C++語言中，對于一個由類名加倆冒號再加成員名構(gòu)成的東西（學(xué)名叫“quilified-id”），比如：A::x，只有當(dāng)x是A類的靜態(tài)成員的時候，A::x才能表示一個左值。而對于函數(shù)類型到函數(shù)指針類型的默認(rèn)轉(zhuǎn)換，只有當(dāng)函數(shù)類型是左值的時候才行

6.關(guān)于c、c++的輸入輸出函數(shù)的掌握：

/***********************************************************************************這個讀取字符的函數(shù)可以把所有的輸入字符都?xì)w結(jié)為' '和非' '兩類，減輕輸入字符后的處理難度。 */ char read_char(void) { int ch = getchar(); if(ch == '\t' || ch == '\n')return ' '; return ch; }

讀入單詞的一個經(jīng)典程序，c現(xiàn)代方法上的
?

/******************************************************************************* len表示讀入的單詞的長度,word是字符指針 *******************************************************************************/ void read_word(char * word,int len) { int ch,pos = 0; while((ch = read_char()) == ' ') //調(diào)用read_char()函數(shù)比getchar()更方便; while(ch != ' ' && ch != EOF) //EOF是文件結(jié)束符，表示linux中CTRL+D或者 win中ctrl+z{if(pos < len)word[pos ++] = ch;ch = read_char(); //如果這里讀入”空格“或者EOF，那么讀入停止} word[pos] = '\0'; //末尾添加\0 }

自己的c語言太菜了，真是無地自容了。

7.

//本程序只有一個主題： //對于代碼中的某個節(jié)點來說，基類的公有成員是否是可訪問的，則派生類向基類的轉(zhuǎn)換也是可訪問的；反之則不行。 //我自己的語言理解這句話是：對于某個用戶來說，如果這個用戶能透過派生類看到（或者使用）基類的公有成員，那么這個用戶就可以使用從派生類向基類的轉(zhuǎn)換；反之，則不行。 //如果上面的難理解，那我就這樣說：某個用戶能否使用派生類對象向基類對象的轉(zhuǎn)換，關(guān)鍵是看對這個用戶來說，能否通過派生類對象使用基類的共有成員,B b;b.pub_men//(如果能這樣使用就對，不能就錯);#include <string> #include <iostream> using namespace std; class A {public:int a= 1;protected:int b = 2;private:int c = 3;};class B:protected A { public: void f()const{A * a;B * b = new B;//下面的這句，能否實現(xiàn)，關(guān)鍵在于這個用戶能否通過派生類看到基類的共有成員。//下面這句的用戶其實就是派生類本身（A是基類，B是派生類），肯定能看見基類的共有成員了//所以下面的語句是合法的a = b; //派生類對象到基類對象的轉(zhuǎn)換cout << "B::b" << b->b << endl;delete b;} };class C:protected B {public:void f(){cout << "A::b" <<b << endl;}};int main() { A * a = new A; B * b = new B; //下面這個語句 c=b 是否合理，關(guān)鍵是這個語句的用戶能否透過派生類(B類)看見基類(A類)的共有成員， //答案是否定的，因為B：protected A，這句話說明了，A類的共有成員在B類中成為了protected成員。 //對于普通用戶而言，B類protected成員是不可見的。所以下面這句代碼匯報錯。 //A * c = b; //使用了派生類對象向基類對象的轉(zhuǎn)換 b->f();delete a; delete b;return 0; }

8.自己在做15.9的課后習(xí)題15.41時候，把OrQuery的eval求并集的set_intersection的函數(shù)中，前兩個迭代器，本應(yīng)該是shared_ptr<set<line_no>>的迭代器，結(jié)果帶入shared_ptr<vector<string>>的迭代器，結(jié)果出現(xiàn)如下看不懂的錯誤：

a.out query.cc quote.h textquery.cc r@r:~/coml/c++/15/15.9/ex/15.41$ g++ main.cc query.cc -o 123 In file included from /usr/include/c++/9/algorithm:62,from query.h:38,from query.cc:7: /usr/include/c++/9/bits/stl_algo.h: In instantiation of ‘_OutputIterator std::__set_intersection(_InputIterator1, _InputIterator1, _InputIterator2, _InputIterator2, _OutputIterator, _Compare) [with _InputIterator1 = __gnu_cxx::__normal_iterator<std::__cxx11::basic_string<char>*, std::vector<std::__cxx11::basic_string<char> > >; _InputIterator2 = __gnu_cxx::__normal_iterator<std::__cxx11::basic_string<char>*, std::vector<std::__cxx11::basic_string<char> > >; _OutputIterator = std::insert_iterator<std::set<long unsigned int> >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]’: /usr/include/c++/9/bits/stl_algo.h:5307:48: required from ‘_OIter std::set_intersection(_IIter1, _IIter1, _IIter2, _IIter2, _OIter) [with _IIter1 = __gnu_cxx::__normal_iterator<std::__cxx11::basic_string<char>*, std::vector<std::__cxx11::basic_string<char> > >; _IIter2 = __gnu_cxx::__normal_iterator<std::__cxx11::basic_string<char>*, std::vector<std::__cxx11::basic_string<char> > >; _OIter = std::insert_iterator<std::set<long unsigned int> >]’ query.h:425:93: required from here /usr/include/c++/9/bits/stl_algo.h:5258:16: error: no match for ‘operator=’ (operand types are ‘std::insert_iterator<std::set<long unsigned int> >’ and ‘std::__cxx11::basic_string<char>’)5258 | *__result = *__first1;| ~~~~~~~~~~^~~~~~~~~~~ In file included from /usr/include/c++/9/bits/stl_algobase.h:67,from /usr/include/c++/9/bits/char_traits.h:39,from /usr/include/c++/9/string:40,from query.cc:1: /usr/include/c++/9/bits/stl_iterator.h:716:7: note: candidate: ‘std::insert_iterator<_Container>& std::insert_iterator<_Container>::operator=(const typename _Container::value_type&) [with _Container = std::set<long unsigned int>; typename _Container::value_type = long unsigned int]’716 | operator=(const typename _Container::value_type& __value)| ^~~~~~~~ /usr/include/c++/9/bits/stl_iterator.h:716:56: note: no known conversion for argument 1 from ‘std::__cxx11::basic_string<char>’ to ‘const value_type&’ {aka ‘const long unsigned int&’}716 | operator=(const typename _Container::value_type& __value)| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~ /usr/include/c++/9/bits/stl_iterator.h:724:7: note: candidate: ‘std::insert_iterator<_Container>& std::insert_iterator<_Container>::operator=(typename _Container::value_type&&) [with _Container = std::set<long unsigned int>; typename _Container::value_type = long unsigned int]’724 | operator=(typename _Container::value_type&& __value)| ^~~~~~~~ /usr/include/c++/9/bits/stl_iterator.h:724:51: note: no known conversion for argument 1 from ‘std::__cxx11::basic_string<char>’ to ‘std::set<long unsigned int>::value_type&&’ {aka ‘long unsigned int&&’}724 | operator=(typename _Container::value_type&& __value)| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~ /usr/include/c++/9/bits/stl_iterator.h:665:11: note: candidate: ‘constexpr std::insert_iterator<std::set<long unsigned int> >& std::insert_iterator<std::set<long unsigned int> >::operator=(const std::insert_iterator<std::set<long unsigned int> >&)’665 | class insert_iterator| ^~~~~~~~~~~~~~~ /usr/include/c++/9/bits/stl_iterator.h:665:11: note: no known conversion for argument 1 from ‘std::__cxx11::basic_string<char>’ to ‘const std::insert_iterator<std::set<long unsigned int> >&’ /usr/include/c++/9/bits/stl_iterator.h:665:11: note: candidate: ‘constexpr std::insert_iterator<std::set<long unsigned int> >& std::insert_iterator<std::set<long unsigned int> >::operator=(std::insert_iterator<std::set<long unsigned int> >&&)’ /usr/include/c++/9/bits/stl_iterator.h:665:11: note: no known conversion for argument 1 from ‘std::__cxx11::basic_string<char>’ to ‘std::insert_iterator<std::set<long unsigned int> >&&’

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