蓝桥ROS机器人之现代C++学习笔记第2章习题

#include <iostream>
#include <map>
#include <string>
#include <functional>

template <typename Key, typename Value, typename F>
void update(std::map<Key, Value>& m, F foo) {
    for (auto&& [key, value] : m ) value = foo(key);
}

int main() {
    std::map<std::string, long long int> m {
        {"a", 1},
        {"b", 2},
        {"c", 3}
    };
    update(m, [](std::string key) -> long long int {
        return std::hash<std::string>{}(key);
    });
    for (auto&& [key, value] : m)
        std::cout << key << ":" << value << std::endl;
}

#include <iostream>
template<typename ... T>
auto average(T ... t) {
    return (t + ... ) / sizeof...(t);
}
int main() {
    std::cout << average(1, 2, 3, 4, 5, 6, 7, 8, 9, 10) << std::endl;
}

shiyanlou:Code/ $ git clone https://github.com/changkun/modern-cpp-tutorial.git
\u6b63\u514b\u9686\u5230 'modern-cpp-tutorial'...
^C
shiyanlou:Code/ $ git clone https://github.com/changkun/modern-cpp-tutorial.git
\u6b63\u514b\u9686\u5230 'modern-cpp-tutorial'...




fatal: unable to access 'https://github.com/changkun/modern-cpp-tutorial.git/': Failed to connect to github.com port 443: \u8fde\u63a5\u8d85\u65f6
shiyanlou:Code/ $                                                    [22:34:28]
shiyanlou:Code/ $                                                    [22:34:28]
shiyanlou:Code/ $                                                    [22:34:28]
shiyanlou:Code/ $                                                    [22:34:28]
shiyanlou:Code/ $ gedit ex1.cpp                                      [22:34:28]

(gedit:266): GVFS-RemoteVolumeMonitor-WARNING **: remote volume monitor with dbus name org.gtk.vfs.UDisks2VolumeMonitor is not supported

(gedit:266): Gtk-WARNING **: Calling Inhibit failed: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.gnome.SessionManager was not provided by any .service files
shiyanlou:Code/ $ g++ -std=c++17 ex1.cpp -o ex1                      [22:36:44]
ex1.cpp: In function \u2018void update(std::map<Key, Value>&, F)\u2019:
ex1.cpp:8:17: error: expected unqualified-id before \u2018[\u2019 token
     for (auto&& [key, value] : m ) value = foo(key);
                 ^
ex1.cpp:8:17: error: expected \u2018;\u2019 before \u2018[\u2019 token
ex1.cpp:8:18: error: \u2018key\u2019 was not declared in this scope
     for (auto&& [key, value] : m ) value = foo(key);
                  ^
ex1.cpp:8:23: error: \u2018value\u2019 was not declared in this scope
     for (auto&& [key, value] : m ) value = foo(key);
                       ^
ex1.cpp: In lambda function:
ex1.cpp:8:30: error: expected \u2018{\u2019 before \u2018:\u2019 token
     for (auto&& [key, value] : m ) value = foo(key);
                              ^
ex1.cpp: In function \u2018void update(std::map<Key, Value>&, F)\u2019:
ex1.cpp:8:30: error: expected \u2018;\u2019 before \u2018:\u2019 token
ex1.cpp:8:30: error: expected primary-expression before \u2018:\u2019 token
ex1.cpp:8:30: error: expected \u2018)\u2019 before \u2018:\u2019 token
ex1.cpp:8:30: error: expected primary-expression before \u2018:\u2019 token
ex1.cpp: In function \u2018int main()\u2019:
ex1.cpp:20:17: error: expected unqualified-id before \u2018[\u2019 token
     for (auto&& [key, value] : m)
                 ^
ex1.cpp:20:17: error: expected \u2018;\u2019 before \u2018[\u2019 token
ex1.cpp:20:18: error: \u2018key\u2019 was not declared in this scope
     for (auto&& [key, value] : m)
                  ^
ex1.cpp:20:23: error: \u2018value\u2019 was not declared in this scope
     for (auto&& [key, value] : m)
                       ^
ex1.cpp: In lambda function:
ex1.cpp:20:30: error: expected \u2018{\u2019 before \u2018:\u2019 token
     for (auto&& [key, value] : m)
                              ^
ex1.cpp: In function \u2018int main()\u2019:
ex1.cpp:20:30: error: expected \u2018;\u2019 before \u2018:\u2019 token
ex1.cpp:20:30: error: expected primary-expression before \u2018:\u2019 token
ex1.cpp:20:30: error: expected \u2018)\u2019 before \u2018:\u2019 token
ex1.cpp:20:30: error: expected primary-expression before \u2018:\u2019 token
shiyanlou:Code/ $ gedit ex2.cpp                                      [22:37:09]

(gedit:317): GVFS-RemoteVolumeMonitor-WARNING **: remote volume monitor with dbus name org.gtk.vfs.UDisks2VolumeMonitor is not supported

(gedit:317): Gtk-WARNING **: Calling Inhibit failed: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.gnome.SessionManager was not provided by any .service files
shiyanlou:Code/ $ g++ -std=c++17 ex2.cpp -o ex2                      [22:40:47]
ex2.cpp: In function \u2018auto average(T ...)\u2019:
ex2.cpp:4:17: error: expected primary-expression before \u2018...\u2019 token
     return (t + ... ) / sizeof...(t);
                 ^
ex2.cpp:4:17: error: expected \u2018)\u2019 before \u2018...\u2019 token
ex2.cpp:4:36: error: parameter packs not expanded with \u2018...\u2019:
     return (t + ... ) / sizeof...(t);
                                    ^
ex2.cpp:4:36: note:         \u2018t\u2019
ex2.cpp: In function \u2018int main()\u2019:
ex2.cpp:7:15: error: no match for \u2018operator<<\u2019 (operand types are \u2018std::ostream {aka std::basic_ostream<char>}\u2019 and \u2018void\u2019)
     std::cout << average(1, 2, 3, 4, 5, 6, 7, 8, 9, 10) << std::endl;
               ^
In file included from /usr/include/c++/5/iostream:39:0,
                 from ex2.cpp:1:
/usr/include/c++/5/ostream:108:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__ostream_type& (*)(std::basic_ostream<_CharT, _Traits>::__ostream_type&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
       operator<<(__ostream_type& (*__pf)(__ostream_type&))
       ^
/usr/include/c++/5/ostream:108:7: note:   no known conversion for argument 1 from \u2018void\u2019 to \u2018std::basic_ostream<char>::__ostream_type& (*)(std::basic_ostream<char>::__ostream_type&) {aka std::basic_ostream<char>& (*)(std::basic_ostream<char>&)}\u2019
/usr/include/c++/5/ostream:117:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__ios_type& (*)(std::basic_ostream<_CharT, _Traits>::__ios_type&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>; std::basic_ostream<_CharT, _Traits>::__ios_type = std::basic_ios<char>]
       operator<<(__ios_type& (*__pf)(__ios_type&))
       ^
/usr/include/c++/5/ostream:117:7: note:   no known conversion for argument 1 from \u2018void\u2019 to \u2018std::basic_ostream<char>::__ios_type& (*)(std::basic_ostream<char>::__ios_type&) {aka std::basic_ios<char>& (*)(std::basic_ios<char>&)}\u2019
/usr/include/c++/5/ostream:127:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::ios_base& (*)(std::ios_base&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
       operator<<(ios_base& (*__pf) (ios_base&))
       ^
/usr/include/c++/5/ostream:127:7: note:   no known conversion for argument 1 from \u2018void\u2019 to \u2018std::ios_base& (*)(std::ios_base&)\u2019
/usr/include/c++/5/ostream:166:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
       operator<<(long __n)
       ^
/usr/include/c++/5/ostream:166:7: note:   no known conversion for argument 1 from \u2018void\u2019 to \u2018long int\u2019
/usr/include/c++/5/ostream:170:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
       operator<<(unsigned long __n)
       ^
/usr/include/c++/5/ostream:170:7: note:   no known conversion for argument 1 from \u2018void\u2019 to \u2018long unsigned int\u2019
/usr/include/c++/5/ostream:174:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(bool) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
       operator<<(bool __n)
       ^
/usr/include/c++/5/ostream:174:7: note:   no known conversion for argument 1 from \u2018void\u2019 to \u2018bool\u2019
In file included from /usr/include/c++/5/ostream:638:0,
                 from /usr/include/c++/5/iostream:39,
                 from ex2.cpp:1:
/usr/include/c++/5/bits/ostream.tcc:91:5: note: candidate: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short int) [with _CharT = char; _Traits = std::char_traits<char>]
     basic_ostream<_CharT, _Traits>::
     ^
/usr/include/c++/5/bits/ostream.tcc:91:5: note:   no known conversion for argument 1 from \u2018void\u2019 to \u2018short int\u2019
In file included from /usr/include/c++/5/iostream:39:0,
                 from ex2.cpp:1:
/usr/include/c++/5/ostream:181:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(short unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
       operator<<(unsigned short __n)
       ^
/usr/include/c++/5/ostream:181:7: note:   no known conversion for argument 1 from \u2018void\u2019 to \u2018short unsigned int\u2019
In file included from /usr/include/c++/5/ostream:638:0,
                 from /usr/include/c++/5/iostream:39,
                 from ex2.cpp:1:
/usr/include/c++/5/bits/ostream.tcc:105:5: note: candidate: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(int) [with _CharT = char; _Traits = std::char_traits<char>]
     basic_ostream<_CharT, _Traits>::
     ^
/usr/include/c++/5/bits/ostream.tcc:105:5: note:   no known conversion for argument 1 from \u2018void\u2019 to \u2018int\u2019
In file included from /usr/include/c++/5/iostream:39:0,
                 from ex2.cpp:1:
/usr/include/c++/5/ostream:192:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
       operator<<(unsigned int __n)
       ^
/usr/include/c++/5/ostream:192:7: note:   no known conversion for argument 1 from \u2018void\u2019 to \u2018unsigned int\u2019
/usr/include/c++/5/ostream:201:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
       operator<<(long long __n)
       ^
/usr/include/c++/5/ostream:201:7: note:   no known conversion for argument 1 from \u2018void\u2019 to \u2018long long int\u2019
/usr/include/c++/5/ostream:205:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
       operator<<(unsigned long long __n)
       ^
/usr/include/c++/5/ostream:205:7: note:   no known conversion for argument 1 from \u2018void\u2019 to \u2018long long unsigned int\u2019
/usr/include/c++/5/ostream:220:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(double) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
       operator<<(double __f)
       ^
/usr/include/c++/5/ostream:220:7: note:   no known conversion for argument 1 from \u2018void\u2019 to \u2018double\u2019
/usr/include/c++/5/ostream:224:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(float) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
       operator<<(float __f)
       ^
/usr/include/c++/5/ostream:224:7: note:   no known conversion for argument 1 from \u2018void\u2019 to \u2018float\u2019
/usr/include/c++/5/ostream:232:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long double) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
       operator<<(long double __f)
       ^
/usr/include/c++/5/ostream:232:7: note:   no known conversion for argument 1 from \u2018void\u2019 to \u2018long double\u2019
/usr/include/c++/5/ostream:245:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(const void*) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
       operator<<(const void* __p)
       ^
/usr/include/c++/5/ostream:245:7: note:   no known conversion for argument 1 from \u2018void\u2019 to \u2018const void*\u2019
In file included from /usr/include/c++/5/ostream:638:0,
                 from /usr/include/c++/5/iostream:39,
                 from ex2.cpp:1:
/usr/include/c++/5/bits/ostream.tcc:119:5: note: candidate: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__streambuf_type*) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__streambuf_type = std::basic_streambuf<char>]
     basic_ostream<_CharT, _Traits>::
     ^
/usr/include/c++/5/bits/ostream.tcc:119:5: note:   no known conversion for argument 1 from \u2018void\u2019 to \u2018std::basic_ostream<char>::__streambuf_type* {aka std::basic_streambuf<char>*}\u2019
In file included from /usr/include/c++/5/iostream:39:0,
                 from ex2.cpp:1:
/usr/include/c++/5/ostream:628:5: note: candidate: template<class _CharT, class _Traits, class _Tp> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&&, const _Tp&)
     operator<<(basic_ostream<_CharT, _Traits>&& __os, const _Tp& __x)
     ^
/usr/include/c++/5/ostream:628:5: note:   template argument deduction/substitution failed:
/usr/include/c++/5/ostream: In substitution of \u2018template<class _CharT, class _Traits, class _Tp> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&&, const _Tp&) [with _CharT = char; _Traits = std::char_traits<char>; _Tp = void]\u2019:
ex2.cpp:7:55:   required from here
/usr/include/c++/5/ostream:628:5: error: forming reference to void
/usr/include/c++/5/ostream:574:5: note: candidate: template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const unsigned char*)
     operator<<(basic_ostream<char, _Traits>& __out, const unsigned char* __s)
     ^
/usr/include/c++/5/ostream:574:5: note:   template argument deduction/substitution failed:
ex2.cpp:7:25: note:   cannot convert \u2018average<{int, int, int, int, int, int, int, int, int, int}>(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)\u2019 (type \u2018void\u2019) to type \u2018const unsigned char*\u2019
     std::cout << average(1, 2, 3, 4, 5, 6, 7, 8, 9, 10) << std::endl;
                         ^
In file included from /usr/include/c++/5/iostream:39:0,
                 from ex2.cpp:1:
/usr/include/c++/5/ostream:569:5: note: candidate: template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const signed char*)
     operator<<(basic_ostream<char, _Traits>& __out, const signed char* __s)
     ^
/usr/include/c++/5/ostream:569:5: note:   template argument deduction/substitution failed:
ex2.cpp:7:25: note:   cannot convert \u2018average<{int, int, int, int, int, int, int, int, int, int}>(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)\u2019 (type \u2018void\u2019) to type \u2018const signed char*\u2019
     std::cout << average(1, 2, 3, 4, 5, 6, 7, 8, 9, 10) << std::endl;
                         ^
In file included from /usr/include/c++/5/iostream:39:0,
                 from ex2.cpp:1:
/usr/include/c++/5/ostream:556:5: note: candidate: template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const char*)
     operator<<(basic_ostream<char, _Traits>& __out, const char* __s)
     ^
/usr/include/c++/5/ostream:556:5: note:   template argument deduction/substitution failed:
ex2.cpp:7:25: note:   cannot convert \u2018average<{int, int, int, int, int, int, int, int, int, int}>(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)\u2019 (type \u2018void\u2019) to type \u2018const char*\u2019
     std::cout << average(1, 2, 3, 4, 5, 6, 7, 8, 9, 10) << std::endl;
                         ^
In file included from /usr/include/c++/5/ostream:638:0,
                 from /usr/include/c++/5/iostream:39,
                 from ex2.cpp:1:
/usr/include/c++/5/bits/ostream.tcc:321:5: note: candidate: template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const char*)
     operator<<(basic_ostream<_CharT, _Traits>& __out, const char* __s)
     ^
/usr/include/c++/5/bits/ostream.tcc:321:5: note:   template argument deduction/substitution failed:
ex2.cpp:7:25: note:   cannot convert \u2018average<{int, int, int, int, int, int, int, int, int, int}>(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)\u2019 (type \u2018void\u2019) to type \u2018const char*\u2019
     std::cout << average(1, 2, 3, 4, 5, 6, 7, 8, 9, 10) << std::endl;
                         ^
In file included from /usr/include/c++/5/iostream:39:0,
                 from ex2.cpp:1:
/usr/include/c++/5/ostream:539:5: note: candidate: template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const _CharT*)
     operator<<(basic_ostream<_CharT, _Traits>& __out, const _CharT* __s)
     ^
/usr/include/c++/5/ostream:539:5: note:   template argument deduction/substitution failed:
ex2.cpp:7:55: note:   mismatched types \u2018const _CharT*\u2019 and \u2018void\u2019
     std::cout << average(1, 2, 3, 4, 5, 6, 7, 8, 9, 10) << std::endl;
                                                       ^
In file included from /usr/include/c++/5/iostream:39:0,
                 from ex2.cpp:1:
/usr/include/c++/5/ostream:519:5: note: candidate: template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, unsigned char)
     operator<<(basic_ostream<char, _Traits>& __out, unsigned char __c)
     ^
/usr/include/c++/5/ostream:519:5: note:   template argument deduction/substitution failed:
ex2.cpp:7:25: note:   cannot convert \u2018average<{int, int, int, int, int, int, int, int, int, int}>(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)\u2019 (type \u2018void\u2019) to type \u2018unsigned char\u2019
     std::cout << average(1, 2, 3, 4, 5, 6, 7, 8, 9, 10) << std::endl;
                         ^
In file included from /usr/include/c++/5/iostream:39:0,
                 from ex2.cpp:1:
/usr/include/c++/5/ostream:514:5: note: candidate: template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, signed char)
     operator<<(basic_ostream<char, _Traits>& __out, signed char __c)
     ^
/usr/include/c++/5/ostream:514:5: note:   template argument deduction/substitution failed:
ex2.cpp:7:25: note:   cannot convert \u2018average<{int, int, int, int, int, int, int, int, int, int}>(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)\u2019 (type \u2018void\u2019) to type \u2018signed char\u2019
     std::cout << average(1, 2, 3, 4, 5, 6, 7, 8, 9, 10) << std::endl;
                         ^
In file included from /usr/include/c++/5/iostream:39:0,
                 from ex2.cpp:1:
/usr/include/c++/5/ostream:508:5: note: candidate: template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, char)
     operator<<(basic_ostream<char, _Traits>& __out, char __c)
     ^
/usr/include/c++/5/ostream:508:5: note:   template argument deduction/substitution failed:
ex2.cpp:7:25: note:   cannot convert \u2018average<{int, int, int, int, int, int, int, int, int, int}>(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)\u2019 (type \u2018void\u2019) to type \u2018char\u2019
     std::cout << average(1, 2, 3, 4, 5, 6, 7, 8, 9, 10) << std::endl;
                         ^
In file included from /usr/include/c++/5/iostream:39:0,
                 from ex2.cpp:1:
/usr/include/c++/5/ostream:502:5: note: candidate: template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, char)
     operator<<(basic_ostream<_CharT, _Traits>& __out, char __c)
     ^
/usr/include/c++/5/ostream:502:5: note:   template argument deduction/substitution failed:
ex2.cpp:7:25: note:   cannot convert \u2018average<{int, int, int, int, int, int, int, int, int, int}>(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)\u2019 (type \u2018void\u2019) to type \u2018char\u2019
     std::cout << average(1, 2, 3, 4, 5, 6, 7, 8, 9, 10) << std::endl;
                         ^
In file included from /usr/include/c++/5/iostream:39:0,
                 from ex2.cpp:1:
/usr/include/c++/5/ostream:497:5: note: candidate: template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, _CharT)
     operator<<(basic_ostream<_CharT, _Traits>& __out, _CharT __c)
     ^
/usr/include/c++/5/ostream:497:5: note:   template argument deduction/substitution failed:
ex2.cpp:7:55: note:   deduced conflicting types for parameter \u2018_CharT\u2019 (\u2018char\u2019 and \u2018void\u2019)
     std::cout << average(1, 2, 3, 4, 5, 6, 7, 8, 9, 10) << std::endl;
                                                       ^
In file included from /usr/include/c++/5/bits/ios_base.h:46:0,
                 from /usr/include/c++/5/ios:42,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from ex2.cpp:1:
/usr/include/c++/5/system_error:209:5: note: candidate: template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::error_code&)
     operator<<(basic_ostream<_CharT, _Traits>& __os, const error_code& __e)
     ^
/usr/include/c++/5/system_error:209:5: note:   template argument deduction/substitution failed:
ex2.cpp:7:25: note:   cannot convert \u2018average<{int, int, int, int, int, int, int, int, int, int}>(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)\u2019 (type \u2018void\u2019) to type \u2018const std::error_code&\u2019
     std::cout << average(1, 2, 3, 4, 5, 6, 7, 8, 9, 10) << std::endl;
                         ^
In file included from /usr/include/c++/5/string:52:0,
                 from /usr/include/c++/5/bits/locale_classes.h:40,
                 from /usr/include/c++/5/bits/ios_base.h:41,
                 from /usr/include/c++/5/ios:42,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from ex2.cpp:1:
/usr/include/c++/5/bits/basic_string.h:5172:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)
     operator<<(basic_ostream<_CharT, _Traits>& __os,
     ^
/usr/include/c++/5/bits/basic_string.h:5172:5: note:   template argument deduction/substitution failed:
ex2.cpp:7:55: note:   mismatched types \u2018const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>\u2019 and \u2018void\u2019
     std::cout << average(1, 2, 3, 4, 5, 6, 7, 8, 9, 10) << std::endl;
                                                       ^
shiyanlou:Code/ $                                                    [22:41:10]
shiyanlou:Code/ $                                                    [22:41:11]