我面临以下问题。假设我有两个(或更多)枚举类,如下所示:
enum class CURSOR { ON, OFF };
enum class ANSI { ON, OFF };
我正在尝试实现一个名为OPTION
的(模板)函数,它能够执行如下操作:
OPTION( CURSOR::ON );
OPTION( ANSI::ON );
我试着用这种方式来实现它:
template <typename T>
inline void OPTION( const T& opt )
{
if( opt == CURSOR::ON ) //do something...;
else if( opt == CURSOR::OFF ) //do something...;
else if( opt == ANSI::ON ) //do something...;
else if( opt == ANSI::OFF ) //do something...;
}
但是,如果我试图编译前面定义的两行代码,则会出现以下错误:
examples/../include/manipulators/csmanip.hpp: In instantiation of 'void osm::OPTION(const T&) [with T = CURSOR]':
examples/manipulators.cpp:190:14: required from here
examples/../include/manipulators/csmanip.hpp:88:18: error: no match for 'operator==' (operand types are 'const osm::CURSOR' and 'osm::ANSI')
88 | else if( opt == ANSI::ON ) enableANSI();
| ~~~~^~~~~~~~~~~
examples/../include/manipulators/csmanip.hpp:88:18: note: candidate: 'operator==(osm::ANSI, osm::ANSI)' (built-in)
examples/../include/manipulators/csmanip.hpp:88:18: note: no known conversion for argument 1 from 'const osm::CURSOR' to 'osm::ANSI'
examples/../include/manipulators/csmanip.hpp:88:18: note: candidate: 'operator==(osm::CURSOR, osm::CURSOR)' (built-in)
examples/../include/manipulators/csmanip.hpp:88:18: note: no known conversion for argument 2 from 'osm::ANSI' to 'osm::CURSOR'
examples/../include/manipulators/csmanip.hpp:89:18: error: no match for 'operator==' (operand types are 'const osm::CURSOR' and 'osm::ANSI')
89 | else if( opt == ANSI::OFF ) disableANSI();
请忽略以下事实:我在代码中的命名空间osm
中定义了它们。
你知道问题出在哪里吗?如果你知道如何构建一个适合这个任务的函数,你知道吗?谢谢。
发布于 2022-06-24 16:42:05
我同意273 k和templatetypedef关于使用重载的说法。
但是,如果您一心想在一个地方拥有一个具有案例处理逻辑的模板,那么您可以这样做:
#include <iostream>
#include <type_traits>
using std::cout;
enum class CURSOR { ON, OFF };
enum class ANSI { ON, OFF };
template <typename T>
void OPTION(T opt) {
if constexpr (std::is_same_v<T, CURSOR>) {
if (opt == CURSOR::ON) cout << "cursor is on\n";
else if (opt == CURSOR::OFF) cout << "cursor is off\n";
} else if constexpr (std::is_same_v<T, ANSI>) {
if (opt == ANSI::ON) cout << "ANSI is on\n";
else if (opt == ANSI::OFF) cout << "ANSI is off\n";
}
}
int main() {
OPTION( CURSOR::ON );
OPTION( ANSI::ON );
}
发布于 2022-06-24 16:15:35
一个选项是编写几个重载函数,每个函数处理不同的枚举类型。例如:
void OPTION(CURSOR c) {
switch (c) {
case CURSOR::ON: /* turn cursor on */; break;
case CURSOR::OFF: /* turn cursor off */; break;
}
}
void OPTION(ANSI a) {
switch (a) {
case ANSI::ON: /* turn ANSI on */; break;
case ANSI::OFF: /* turn ANSI off */; break;
}
}
然后,重载解析将选择正确的函数来调用:
OPTION(CURSOR::OFF); // Calls first function
OPTION(ANSI::ON); // Calls second function
https://stackoverflow.com/questions/72746726
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