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- Why the switch statement cannot be applied on strings? 18 answers
- 为什么switch语句不能应用于字符串？ 18个答案
I'm getting the error "Expression must have integral or enum type" on the switch statement 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switch语句中得到错误“Expression必须具有整数或枚举类型”。我已经盯着它看了一会儿，无法弄清楚是怎么回事。任何见解都非常感激。
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":
}
}
}
2 个解决方案
#1
2
The error is clear. You can only use integral types (integer, enum, char etc. which are convertible to integral value), or any expression that evaluates to an integral type in switch statement.
错误很明显。您只能使用整数类型（整数，枚举，字符等可转换为整数值），或任何在switch语句中求值为整数类型的表达式。
#2
1
params[0] has type of std::string. You can't use std::string type (which is not integral) as a switch parameter. 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]具有std :: string类型。您不能将std :: string类型（不是整数）用作switch参数。如果您确信字符串不为空，请使用switch（param [0] [0]）和case“d”。但在这种情况下，您只能切换一个字符的字符串。如果你需要切换更长的字符串，你需要使用if-else的序列if-else if -....
#1
2
The error is clear. You can only use integral types (integer, enum, char etc. which are convertible to integral value), or any expression that evaluates to an integral type in switch statement.
错误很明显。您只能使用整数类型（整数，枚举，字符等可转换为整数值），或任何在switch语句中求值为整数类型的表达式。
#2
1
params[0] has type of std::string. You can't use std::string type (which is not integral) as a switch parameter. 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]具有std :: string类型。您不能将std :: string类型（不是整数）用作switch参数。如果您确信字符串不为空，请使用switch（param [0] [0]）和case“d”。但在这种情况下，您只能切换一个字符的字符串。如果你需要切换更长的字符串，你需要使用if-else的序列if-else if -....