错误:开关量不是整数
我已经通过 StackOverflow 和多谷歌链接研究了我的问题，但我仍然感到困惑.我认为对我来说最好的事情就是问...
I have researched my issue all over StackOverflow and multi-google links, and I am still confused. I figured the best thing for me is ask...
我正在创建一个简单的命令行计算器.到目前为止，这是我的代码:
Im creating a simple command line calculator. Here is my code so far:
const std::string Calculator::SIN("sin");
const std::string Calculator::COS("cos");
const std::string Calculator::TAN("tan");
const std::string Calculator::LOG( "log" );
const std::string Calculator::LOG10( "log10" );
void Calculator::set_command( std::string cmd ) {
for(unsigned i = 0; i < cmd.length(); i++)
{
cmd[i] = tolower(cmd[i]);
}
command = cmd;
}
bool Calculator::is_legal_command() const {
switch(command)
{
case TAN:
case SIN:
case COS:
case LOG:
case LOG10:
return true;
break;
default:
return false;
break;
}
}
我得到的错误是:
Calculator.cpp: In member function 'bool Calculator::is_trig_command() const':
Calculator.cpp: error: switch quantity not an integer
Calculator.cpp: error: 'Calculator::TAN' cannot appear in a constant-expression
Calculator.cpp: error: 'Calculator::SIN' cannot appear in a constant-expression
Calculator.cpp: error: 'Calculator::COS' cannot appear in a constant-expression
强大的互联网，它说允许在 switch 语句中使用字符串.
The mighty internet, it says strings are allowed to be used in switch statements.
谢谢大家，感谢您的帮助.
Thanks everyone, I appreciate your help.
推荐答案
在switch中，表达式必须是an 整数类型或具有明确转换为整数类型的类类型" (引用 VS2008 文档).
In switch, the expression must be of "an integral type or of a class type for which there is an unambiguous conversion to integral type" (quoting VS2008 docs).
字符串类没有像 char 那样明确转换为整数类型".
A string class doesn't have "unambiguous conversion to integral type", like a char does.
作为一种解决方法:
创建一个
map并开启map的值:switch(command_map[command])`
做一组if/else代替switch.更烦人且难以阅读，所以我推荐地图路线.
Do a set of if/else instead of switch. Much more annoying and hard to read, so I'd recommend the map route.
顺便说一句，对于真正复杂的逻辑，一个更好的解决方案是改进映射解决方案以完全摆脱 switch 并使用函数查找:std::地图<std::string, functionPointerType>.您的特定情况可能不需要它，但对于复杂的非常长的查找逻辑来说要快得多.
As an aside, an even better solution for really complicated logic like that is to improve the mapping solution to get rid of switch completely and instead go with a function lookup: std::map<std::string, functionPointerType>. It may not be needed for your specific case, but is MUCH faster for complicated very long look-up logic.
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