C++ 错误：“表达式必须具有整数或枚举类型”
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C++ Error: "Expression must have integral or enum type"
提问by user3629533
I'm getting the error "Expression must have integral or enum type"on the switchstatement of my (incomplete) function below. I've stared at it for a while and can't figure out what the matter is. Any insight greatly appreciated.
我在下面的（不完整）函数的语句中收到错误“表达式必须具有整数或枚举类型”switch。我盯着它看了一会儿，不知道是怎么回事。任何见解都非常感谢。
std::string CWDriver::eval_input(std::string expr)
{
std::vector<std::string> params(split_string(expr, " "));
std::string output("");
if (params.size() == 0)
{
output = "Input cannot be empty.\n";
}
else
{
switch (params[0])
{
case "d":
}
}
}
回答by Rakib
The error is clear. You can only use integraltypes (integer, enum, charetc. which are convertibleto integralvalue), or any expressionthat evaluates to an integral type in switchstatement.
错误很明显。您只能使用积分类型（integer，enum，char等它们转换到integral值），或任何表达，其值在整型switch声明。
回答by Paul
params[0]has type of std::string. You can't use std::stringtype (which is not integral) as a switchparameter. If you are confident strings are not empty use switch (param[0][0])and case 'd'. But in this case you will be able to switch over one-character strings only. If you need to switch over longer strings you need to use the sequence of if-else if-else if-....
params[0]类型为std::string. 您不能使用std::string类型（不是整数）作为switch参数。如果您确信字符串不是空的，请使用switch (param[0][0])和case 'd'。但在这种情况下，您将只能切换一个字符的字符串。如果需要切换更长的字符串，则需要使用if-else if-else if-....
