c++:数据类型的判断type_traits

//判断左值右值引用
void main()
{
	int i(10);//i是左值  有内存实体
	int &ri(i);
	int &&rri(i + 5);//右值引用
	cout << is_lvalue_reference<decltype(i)>::value << endl;//是左值不是引用 输出0
	cout << is_lvalue_reference<decltype(ri)>::value << endl;//是左值引用输出1
	cout << is_lvalue_reference<decltype(rri)>::value << endl;//是右值引用输出0
	cin.get();
}


//此处的 decltype 引用常量都可以获取
//检测是否是数组
void main()
{
	int a[5];
	int *p = a;
	cout << is_array<decltype(a)>::value << endl;//数组输出1
	cout << is_array<decltype(p)>::value << endl;//非数组输出0
	cin.get();
}



void main()
{
	int num = 123;
	double db = 23;
	cout << is_integral<decltype(num)>::value << endl;//判断数据类型  int  1
	cout << is_integral<decltype(db)>::value << endl;//不是int型  0

	string str1;//cpp中的string也是个类
	cout << is_class<string>::value << endl;//1
	cout << is_class<decltype(str1)>::value << endl;//1
	cin.get();
}



template<class T1,class T2>
void same(const T1 &t1, const T2&t2)
{
	cout << is_same<T1, T2>::value << endl;//判定类型是否相等
}
//判断模板的数据类型
void main()
{
	same(12, 34);//一样的数据类型输出  1
	same(12, 34.23);//不一样输出   0
	same('A', 34);//0
	same("sdjbjabf", 34);//0
	cin.get();
}



template<class T1, class T2>
void same2(const T1 &t1, const T2&t2)
{
	//cout << typeid(T1).name() << is_integral(t1) << endl;//error
	cout << typeid(T1).name() << "    " << typeid(t1).name() << "    " << is_integral<T1>::value << endl;
	cout << is_same<T1, T2>::value << endl;
}
//判断模板的数据类型
void main()
{
	same2(12, 34);
	same2(12, 34.23);
	same2('A', 34);
	same2("sdjbjabf", 34);
	cin.get();
}




int add()
{
	return 0;
}
double check()
{
	return 0;
}
class A
{};
class B
{};
template<typename T1,typename T2>
void check_type(const T1 &t1, const T2 &t2,typename enable_if<is_same<T1,T2>::value>::type*p=nullptr)
{
	cout << t1<<"	"<<t2 <<":类型相同"<< endl;
}
template<typename T1, typename T2>
void check_type(const T1 &t1, const T2 &t2, typename enable_if<!is_same<T1, T2>::value>::type*p = nullptr)
{
	cout << t1 << "	" << t2 << ":类型不相同" << endl;
}
//模板与type判断类型的异同   根据参数类型自动选择模板
void main()
{
	check_type(12, 34);
	check_type(12.34, 0.12);
	check_type(12, 34.0);

	check_type(12, (float)34);
	check_type((int)12.34, (int)0.12);

	check_type('A','\n');
	check_type("1234", "abcd");

	check_type(add, check);
	A a;
	B b;
	check_type(&a, &b);
	cin.get();
}


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||=== Build file: "no target" in "no project" (compiler: unknown) ===| E:\C++\2\main.cpp||In function 'int main()':| E:\C++\2\main.cpp|11|error: no match for 'operator>>' (operand types are 'std::basic_istream<char>::__istream_type' {aka 'std::basic_istream<char>'} and '<unresolved overloaded function type>')| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|120|note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__istream_type& (*)(std::basic_istream<_CharT, _Traits>::__istream_type&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|120|note: no known conversion for argument 1 from '<unresolved overloaded function type>' to 'std::basic_istream<char>::__istream_type& (*)(std::basic_istream<char>::__istream_type&)' {aka 'std::basic_istream<char>& (*)(std::basic_istream<char>&)'}| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|124|note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__ios_type& (*)(std::basic_istream<_CharT, _Traits>::__ios_type&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>; std::basic_istream<_CharT, _Traits>::__ios_type = std::basic_ios<char>]'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|124|note: no known conversion for argument 1 from '<unresolved overloaded function type>' to 'std::basic_istream<char>::__ios_type& (*)(std::basic_istream<char>::__ios_type&)' {aka 'std::basic_ios<char>& (*)(std::basic_ios<char>&)'}| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|131|note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::ios_base& (*)(std::ios_base&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|131|note: no known conversion for argument 1 from '<unresolved overloaded function type>' to 'std::ios_base& (*)(std::ios_base&)'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|168|note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(bool&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|168|note: no known conversion for argument 1 from '<unresolved overloaded function type>' to 'bool&'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|172|note: candidate: 'std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(short int&) [with _CharT = char; _Traits = std::char_traits<char>]'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|172|note: no known conversion for argument 1 from '<unresolved overloaded function type>' to 'short int&'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|175|note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(short unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|175|note: no known conversion for argument 1 from '<unresolved overloaded function type>' to 'short unsigned int&'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|179|note: candidate: 'std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(int&) [with _CharT = char; _Traits = std::char_traits<char>]'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|179|note: no known conversion for argument 1 from '<unresolved overloaded function type>' to 'int&'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|182|note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|182|note: no known conversion for argument 1 from '<unresolved overloaded function type>' to 'unsigned int&'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|186|note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|186|note: no known conversion for argument 1 from '<unresolved overloaded function type>' to 'long int&'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|190|note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|190|note: no known conversion for argument 1 from '<unresolved overloaded function type>' to 'long unsigned int&'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|195|note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|195|note: no known conversion for argument 1 from '<unresolved overloaded function type>' to 'long long int&'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|199|note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|199|note: no known conversion for argument 1 from '<unresolved overloaded function type>' to 'long long unsigned int&'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|214|note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(float&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|214|note: no known conversion for argument 1 from '<unresolved overloaded function type>' to 'float&'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|218|note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(double&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|218|note: no known conversion for argument 1 from '<unresolved overloaded function type>' to 'double&'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|222|note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long double&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|222|note: no known conversion for argument 1 from '<unresolved overloaded function type>' to 'long double&'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|235|note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(void*&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|235|note: no known conversion for argument 1 from '<unresolved overloaded function type>' to 'void*&'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|259|note: candidate: 'std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__streambuf_type*) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__streambuf_type = std::basic_streambuf<char>]'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|259|note: no known conversion for argument 1 from '<unresolved overloaded function type>' to 'std::basic_istream<char>::__streambuf_type*' {aka 'std::basic_streambuf<char>*'}| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\bits\basic_string.tcc|1465|note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\bits\basic_string.tcc|1465|note: template argument deduction/substitution failed:| E:\C++\2\main.cpp|11|note: couldn't deduce template parameter '_Alloc'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\bits\istream.tcc|931|note: candidate: 'std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, _CharT&) [with _CharT = char; _Traits = std::char_traits<char>]'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\bits\istream.tcc|931|note: no known conversion for argument 2 from '<unresolved overloaded function type>' to 'char&'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|756|note: candidate: 'template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, unsigned char&)'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|756|note: template argument deduction/substitution failed:| E:\C++\2\main.cpp|11|note: cannot convert 'std::endl' (type '<unresolved overloaded function type>') to type 'unsigned char&'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|761|note: candidate: 'template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, signed char&)'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|761|note: template argument deduction/substitution failed:| E:\C++\2\main.cpp|11|note: cannot convert 'std::endl' (type '<unresolved overloaded function type>') to type 'signed char&'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|799|note: candidate: 'std::basic_istream<_CharT2, _Traits2>& std::operator>>(std::basic_istream<_CharT2, _Traits2>&, _CharT2*) [with _CharT2 = char; _Traits2 = std::char_traits<char>; _CharT = char; _Traits = std::char_traits<char>]'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|799|note: no known conversion for argument 2 from '<unresolved overloaded function type>' to 'char*'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|803|note: candidate: 'template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, unsigned char*)'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|803|note: template argument deduction/substitution failed:| E:\C++\2\main.cpp|11|note: cannot convert 'std::endl' (type '<unresolved overloaded function type>') to type 'unsigned char*'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|808|note: candidate: 'template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, signed char*)'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|808|note: template argument deduction/substitution failed:| E:\C++\2\main.cpp|11|note: cannot convert 'std::endl' (type '<unresolved overloaded function type>') to type 'signed char*'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|980|note: candidate: 'template<class _Istream, class _Tp> typename std::enable_if<std::__and_<std::__not_<std::is_lvalue_reference<_Tp> >, std::__is_convertible_to_basic_istream<_Istream>, std::__is_extractable<typename std::__is_convertible_to_basic_istream<_Tp>::__istream_type, _Tp&&, void> >::value, typename std::__is_convertible_to_basic_istream<_Tp>::__istream_type>::type std::operator>>(_Istream&&, _Tp&&)'| E:\CodeBlocks\MinGW\lib\gcc\x86_64-w64-mingw32\8.1.0\include\c++\istream|980|note: template argument deduction/substitution failed:| E:\C++\2\main.cpp|11|note: couldn't deduce template parameter '_Tp'| E:\C++\2\main.cpp|12|error: 'class cube' has no member named 'setchang'| E:\C++\2\main.cpp|13|error: 'class cube' has no member named 'getchang'| ||=== Build failed: 3 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===| 是什么意思,怎么解决
最新发布
07-17
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