例如:
int a = 12;
cout << typeof(a) << endl;
预期的输出:
int
例如:
int a = 12;
cout << typeof(a) << endl;
预期的输出:
int
当前回答
涉及RTTI (typeid)的其他答案可能是您想要的,只要:
您可以承担内存开销(对于某些编译器,这可能相当大) 编译器返回的类名很有用
另一种选择(类似于Greg Hewgill的答案)是建立一个特征的编译时表。
template <typename T> struct type_as_string;
// declare your Wibble type (probably with definition of Wibble)
template <>
struct type_as_string<Wibble>
{
static const char* const value = "Wibble";
};
注意,如果你将声明包装在宏中,你将在声明带有多个参数的模板类型时遇到麻烦(例如std::map),这是由于逗号的原因。
要访问变量类型的名称,您所需要的是
template <typename T>
const char* get_type_as_string(const T&)
{
return type_as_string<T>::value;
}
其他回答
Try:
#include <typeinfo>
// …
std::cout << typeid(a).name() << '\n';
您可能必须在编译器选项中激活RTTI才能使其工作。此外,它的输出取决于编译器。它可能是一个原始类型名称或名称混乱符号或介于两者之间的任何东西。
不要忘记包含<typeinfo>
我相信您所指的是运行时类型标识。你可以通过做来达到以上目的。
#include <iostream>
#include <typeinfo>
using namespace std;
int main() {
int i;
cout << typeid(i).name();
return 0;
}
对于一些不同的东西,这里有一个类型的“To English”转换,解构每个限定符、范围、参数等等,递归地构建描述类型的字符串,我认为“演绎这个”建议将有助于减少许多特殊化。无论如何,这是一个有趣的晨练,尽管过度膨胀。:)
struct X {
using T = int *((*)[10]);
T f(T, const unsigned long long * volatile * );
};
int main() {
std::cout << describe<decltype(&X::f)>() << std::endl;
}
输出:
pointer to member function of class 1X taking (pointer to array[10]
of pointer to int, pointer to volatile pointer to const unsigned
long long), and returning pointer to array[10] of pointer to int
代码如下: https://godbolt.org/z/7jKK4or43
注:最新版本在我的github: https://github.com/cuzdav/type_to_string
// Print types as strings, including functions, member
#include <type_traits>
#include <typeinfo>
#include <string>
#include <utility>
namespace detail {
template <typename T> struct Describe;
template <typename T, class ClassT>
struct Describe<T (ClassT::*)> {
static std::string describe();
};
template <typename RetT, typename... ArgsT>
struct Describe<RetT(ArgsT...)> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...)> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) const> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) volatile> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) noexcept> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) const volatile> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) const noexcept> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) volatile noexcept> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) const volatile noexcept> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...)&> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) const &> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) volatile &> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) & noexcept> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) const volatile &> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) const & noexcept> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) volatile & noexcept> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) const volatile & noexcept> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) &&> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) const &&> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) volatile &&> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) && noexcept> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) const volatile &&> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) const && noexcept> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) volatile && noexcept> {
static std::string describe();
};
template <typename RetT, class ClassT, typename... ArgsT>
struct Describe<RetT(ClassT::*)(ArgsT...) const volatile && noexcept> {
static std::string describe();
};
template <typename T>
std::string describe()
{
using namespace std::string_literals;
auto terminal = [&](char const * desc) {
return desc + " "s + typeid(T).name();
};
if constexpr(std::is_const_v<T>) {
return "const " + describe<std::remove_const_t<T>>();
}
else if constexpr(std::is_volatile_v<T>) {
return "volatile " + describe<std::remove_volatile_t<T>>();
}
else if constexpr (std::is_same_v<bool, T>) {
return "bool";
}
else if constexpr(std::is_same_v<char, T>) {
return "char";
}
else if constexpr(std::is_same_v<signed char, T>) {
return "signed char";
}
else if constexpr(std::is_same_v<unsigned char, T>) {
return "unsigned char";
}
else if constexpr(std::is_unsigned_v<T>) {
return "unsigned " + describe<std::make_signed_t<T>>();
}
else if constexpr(std::is_void_v<T>) {
return "void";
}
else if constexpr(std::is_integral_v<T>) {
if constexpr(std::is_same_v<short, T>)
return "short";
else if constexpr(std::is_same_v<int, T>)
return "int";
else if constexpr(std::is_same_v<long, T>)
return "long";
else if constexpr(std::is_same_v<long long, T>)
return "long long";
}
else if constexpr(std::is_same_v<float, T>) {
return "float";
}
else if constexpr(std::is_same_v<double, T>) {
return "double";
}
else if constexpr(std::is_same_v<long double, T>) {
return "long double";
}
else if constexpr(std::is_same_v<std::nullptr_t, T>) {
return "nullptr_t";
}
else if constexpr(std::is_class_v<T>) {
return terminal("class");
}
else if constexpr(std::is_union_v<T>) {
return terminal("union");
}
else if constexpr(std::is_enum_v<T>) {
std::string result;
if (!std::is_convertible_v<T, std::underlying_type_t<T>>) {
result += "scoped ";
}
return result + terminal("enum");
}
else if constexpr(std::is_pointer_v<T>) {
return "pointer to " + describe<std::remove_pointer_t<T>>();
}
else if constexpr(std::is_lvalue_reference_v<T>) {
return "lvalue-ref to " + describe<std::remove_reference_t<T>>();
}
else if constexpr(std::is_rvalue_reference_v<T>) {
return "rvalue-ref to " + describe<std::remove_reference_t<T>>();
}
else if constexpr(std::is_bounded_array_v<T>) {
return "array[" + std::to_string(std::extent_v<T>) + "] of " +
describe<std::remove_extent_t<T>>();
}
else if constexpr(std::is_unbounded_array_v<T>) {
return "array[] of " + describe<std::remove_extent_t<T>>();
}
else if constexpr(std::is_function_v<T>) {
return Describe<T>::describe();
}
else if constexpr(std::is_member_object_pointer_v<T>) {
return Describe<T>::describe();
}
else if constexpr(std::is_member_function_pointer_v<T>) {
return Describe<T>::describe();
}
}
template <typename RetT, typename... ArgsT>
std::string Describe<RetT(ArgsT...)>::describe() {
std::string result = "function taking (";
((result += detail::describe<ArgsT>(", ")), ...);
return result + "), returning " + detail::describe<RetT>();
}
template <typename T, class ClassT>
std::string Describe<T (ClassT::*)>::describe() {
return "pointer to member of " + detail::describe<ClassT>() +
" of type " + detail::describe<T>();
}
struct Comma {
char const * sep = "";
std::string operator()(std::string const& str) {
return std::exchange(sep, ", ") + str;
}
};
enum Qualifiers {NONE=0, CONST=1, VOLATILE=2, NOEXCEPT=4, LVREF=8, RVREF=16};
template <typename RetT, typename ClassT, typename... ArgsT>
std::string describeMemberPointer(Qualifiers q) {
std::string result = "pointer to ";
if (NONE != (q & CONST)) result += "const ";
if (NONE != (q & VOLATILE)) result += "volatile ";
if (NONE != (q & NOEXCEPT)) result += "noexcept ";
if (NONE != (q & LVREF)) result += "lvalue-ref ";
if (NONE != (q & RVREF)) result += "rvalue-ref ";
result += "member function of " + detail::describe<ClassT>() + " taking (";
Comma comma;
((result += comma(detail::describe<ArgsT>())), ...);
return result + "), and returning " + detail::describe<RetT>();
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...)>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(NONE);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) const>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(CONST);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) noexcept>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(NOEXCEPT);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) volatile>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(VOLATILE);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) volatile noexcept>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(VOLATILE | NOEXCEPT);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) const volatile>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(CONST | VOLATILE);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) const noexcept>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(CONST | NOEXCEPT);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) const volatile noexcept>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(CONST | VOLATILE | NOEXCEPT);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) &>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(LVREF);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) const &>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(LVREF | CONST);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) & noexcept>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(LVREF | NOEXCEPT);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) volatile &>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(LVREF | VOLATILE);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) volatile & noexcept>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(LVREF | VOLATILE | NOEXCEPT);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) const volatile &>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(LVREF | CONST | VOLATILE);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) const & noexcept>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(LVREF | CONST | NOEXCEPT);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) const volatile & noexcept>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(LVREF | CONST | VOLATILE | NOEXCEPT);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...)&&>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(RVREF);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) const &&>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(RVREF | CONST);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) && noexcept>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(RVREF | NOEXCEPT);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) volatile &&>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(RVREF | VOLATILE);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) volatile && noexcept>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(RVREF | VOLATILE | NOEXCEPT);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) const volatile &&>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(RVREF | CONST | VOLATILE);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) const && noexcept>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(RVREF | CONST | NOEXCEPT);
}
template <typename RetT, class ClassT, typename... ArgsT>
std::string Describe<RetT(ClassT::*)(ArgsT...) const volatile && noexcept>::describe() {
return describeMemberPointer<RetT, ClassT, ArgsT...>(RVREF | CONST | VOLATILE | NOEXCEPT);
}
} // detail
///////////////////////////////////
// Main function
///////////////////////////////////
template <typename T>
std::string describe() {
return detail::describe<T>();
}
///////////////////////////////////
// Sample code
///////////////////////////////////
#include <iostream>
struct X {
using T = int *((*)[10]);
T f(T, const unsigned long long * volatile * );
};
int main() {
std::cout << describe<decltype(&X::f)>() << std::endl;
}
c++在编译时使用模板和运行时使用TypeId进行数据类型解析。
编译时解决方案。
template <std::size_t...Idxs>
constexpr auto substring_as_array(std::string_view str, std::index_sequence<Idxs...>)
{
return std::array{str[Idxs]..., '\n'};
}
template <typename T>
constexpr auto type_name_array()
{
#if defined(__clang__)
constexpr auto prefix = std::string_view{"[T = "};
constexpr auto suffix = std::string_view{"]"};
constexpr auto function = std::string_view{__PRETTY_FUNCTION__};
#elif defined(__GNUC__)
constexpr auto prefix = std::string_view{"with T = "};
constexpr auto suffix = std::string_view{"]"};
constexpr auto function = std::string_view{__PRETTY_FUNCTION__};
#elif defined(_MSC_VER)
constexpr auto prefix = std::string_view{"type_name_array<"};
constexpr auto suffix = std::string_view{">(void)"};
constexpr auto function = std::string_view{__FUNCSIG__};
#else
# error Unsupported compiler
#endif
constexpr auto start = function.find(prefix) + prefix.size();
constexpr auto end = function.rfind(suffix);
static_assert(start < end);
constexpr auto name = function.substr(start, (end - start));
return substring_as_array(name, std::make_index_sequence<name.size()>{});
}
template <typename T>
struct type_name_holder {
static inline constexpr auto value = type_name_array<T>();
};
template <typename T>
constexpr auto type_name() -> std::string_view
{
constexpr auto& value = type_name_holder<T>::value;
return std::string_view{value.data(), value.size()};
}
运行时的解决方案。
template <typename T>
void PrintDataType(T type)
{
auto name = typeid(type).name();
string cmd_str = "echo '" + string(name) + "' | c++filt -t";
system(cmd_str.c_str());
}
主要代码
#include <iostream>
#include <map>
#include <string>
#include <typeinfo>
#include <string_view>
#include <array> // std::array
#include <utility> // std::index_sequence
using std::string;
int main () { / /动态分辨率。 std::map<int, int> iMap; PrintDataType (iMap); //编译类型解析。 std:: cout < < type_name < std::列表< int > > () < < std:: endl; 返回0; }
代码片段
Howard Hinnant使用魔法数字提取类型名称。康桓瑋建议字符串前缀和后缀。但是前缀/后缀一直在变化。 使用" probe_type " type_name自动计算" probe_type "的前缀和后缀大小,以提取类型名称:
#include <string_view>
using namespace std;
namespace typeName {
template <typename T>
constexpr string_view wrapped_type_name () {
#ifdef __clang__
return __PRETTY_FUNCTION__;
#elif defined(__GNUC__)
return __PRETTY_FUNCTION__;
#elif defined(_MSC_VER)
return __FUNCSIG__;
#endif
}
class probe_type;
constexpr string_view probe_type_name ("typeName::probe_type");
constexpr string_view probe_type_name_elaborated ("class typeName::probe_type");
constexpr string_view probe_type_name_used (wrapped_type_name<probe_type> ().find (probe_type_name_elaborated) != -1 ? probe_type_name_elaborated : probe_type_name);
constexpr size_t prefix_size () {
return wrapped_type_name<probe_type> ().find (probe_type_name_used);
}
constexpr size_t suffix_size () {
return wrapped_type_name<probe_type> ().length () - prefix_size () - probe_type_name_used.length ();
}
template <typename T>
string_view type_name () {
constexpr auto type_name = wrapped_type_name<T> ();
return type_name.substr (prefix_size (), type_name.length () - prefix_size () - suffix_size ());
}
}
#include <iostream>
using typeName::type_name;
using typeName::probe_type;
class test;
int main () {
cout << type_name<class test> () << endl;
cout << type_name<const int*&> () << endl;
cout << type_name<unsigned int> () << endl;
const int ic = 42;
const int* pic = ⁣
const int*& rpic = pic;
cout << type_name<decltype(ic)> () << endl;
cout << type_name<decltype(pic)> () << endl;
cout << type_name<decltype(rpic)> () << endl;
cout << type_name<probe_type> () << endl;
}
输出
gcc 10.2:
test
const int *&
unsigned int
const int
const int *
const int *&
typeName::probe_type
铿锵声11.0.0:
test
const int *&
unsigned int
const int
const int *
const int *&
typeName::probe_type
VS 2019版本16.7.6:
class test
const int*&
unsigned int
const int
const int*
const int*&
class typeName::probe_type