我正在阅读Bjarne Stroustrup的“The C++ Programming Language”第4版。在本书的第一部分,我发现using
的使用看起来像以下:如何使用模板在C++中使用`(使参数化别名)进行别名?
// Error is in these 2 lines
template<typename T>
using Iterator<T> = typename T::iterator;
*参见[**]为完整的程序和错误消息*
这正是我在105页面发现当我把这个变成一个完整的程序,并试图编译它,g++
给了我这个错误masseage:
> g++ -std=c++14 -o fnd find_all.cpp
find_all.cpp:13:15: error: expected '=' before '<' token
using Iterator<T> = typename T::iterator;
^
find_all.cpp:13:15: error: expected type-specifier before '<' token
我不能鳍d在这段代码中的任何问题,(我是新的C++,我无法找到我的小知识问题)(更多容易混淆的,我发现这个上了Bjarne的书)
有人能告诉我为什么该代码是否会产生错误?
注意:但是,如果我用
typename C::iterator
替换Iterator<C>
(见下文),它工作正常,没有错误!
[**]完整的计划和错误消息:
// Error is in these 2 lines
template<typename T>
using Iterator<T> = typename T::iterator;
// -------------------------------------------
// For the completeness I'll include my complete program here
template<typename C, typename V>
vector<Iterator<C>> find_all(C& c, V v) // find all occurrences of v in c
{
vector<Iterator<C>> res;
for (auto p = c.begin(); p!=c.end(); ++p)
if (∗p==v)
res.push_back(p);
return res;
}
void test()
{
string m {"Mary had a little lamb"};
for (auto p : find_all(m, 'a'))
if (*p == 'a')
cerr << "string bug!\n";
list<double> ld { 1.1, 2.2, 3.3, 4.4, 5.5, 6.6, 1.1, 1.1 };
for (auto p : find_all(ld, 1.1))
if (*p == 1.1)
cerr << "list bug!\n";
vector<string> strv { "blue", "yellow", "red", "white", "orange", "blue" };
for (auto p : find_all(strv, "blue"))
if (*p == "blue")
cerr << "string vector bug!\n";
}
int main(void)
{
test();
return 0;
}
错误消息:
> g++ -std=c++14 -o fnd find_all.cpp
find_all.cpp:13:15: error: expected '=' before '<' token
using Iterator<T> = typename T::iterator;
^
find_all.cpp:13:15: error: expected type-specifier before '<' token
find_all.cpp:16:8: error: 'Iterator' was not declared in this scope
vector<Iterator<C>> find_all(C& c, V v)
^
find_all.cpp:16:17: error: template argument 1 is invalid
vector<Iterator<C>> find_all(C& c, V v)
^
find_all.cpp:16:17: error: template argument 2 is invalid
find_all.cpp:16:18: error: expected unqualified-id before '>' token
vector<Iterator<C>> find_all(C& c, V v)
^
find_all.cpp: In function 'void test()':
find_all.cpp:30:31: error: 'find_all' was not declared in this scope
for (auto p : find_all(m, 'a'))
^
find_all.cpp:35:32: error: 'find_all' was not declared in this scope
for (auto p : find_all(ld, 1.1))
^
find_all.cpp:40:37: error: 'find_all' was not declared in this scope
for (auto p : find_all(strv, "blue"))
非常感谢你,现在工作得很好。这本书似乎是一个错字,谢谢 – 0xEDD1E