从char的C ++枚举 [英] C++ enum from char
本文介绍了从char的C ++枚举的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
好吧,我是C ++的新人。我得到了Bjarne的书,我试图遵循计算器代码。
但是,编译器吐出一个关于这一部分的错误:
token_value get_token()
{
char ch;
do {//跳过空格除了'\\\
'
if(!std :: cin.get(ch))return curr_tok = END;
} while(ch!='\\\
'&& isspace(ch));
switch(ch){
case';':
case'\\\
':
std :: cin> WS; // skip whitespace
return curr_tok = PRINT;
case'*':
case'/':
case'+':
case' - ':
case'(':
case ')':
case'=':
return curr_tok = ch;
case'0':case'1':case'2':case'3':case'4':case'5':
case'6':case' 8':case'9':case'。':
std :: cin.putback(ch);
std :: cin>> number_value;
return curr_tok = NUMBER;
默认值:// NAME,NAME =或错误
if(isalpha(ch)){
char * p = name_string;
* p ++ = ch;
while(std :: cin.get(ch)&& isalnum(ch))* p ++ = ch;
std :: cin.putback(ch);
* p = 0;
return curr_tok = NAME;
}
错误(bad token);
return curr_tok = PRINT;
}
它吐出的错误是:
calc.cpp:42:错误:从'char'到'token_value'无效转换
token_value
是一个枚举,如下所示:
enum token_value {
NAME,NUMBER,END,
PLUS ='+',MINUS =' - ',MUL ='*',DIV ='/',
PRINT =';',ASSIGN ='=',LP ='(',RP =')'
};
token_value curr_tok;
我的问题是,如何将ch(从cin)转换为相关的枚举值? / p>
解决方案
您不能从 char
$ c> enum - 你必须明确地做:
return curr_tok = static_cast< token_value> (ch)。
但要小心!如果您的 enum
值没有匹配您的 char
,那么很难使用结果:)
Ok, I'm new at C++. I got Bjarne's book, and I'm trying to follow the calculator code.
However, the compiler is spitting out an error about this section:
token_value get_token()
{
char ch;
do { // skip whitespace except '\n'
if(!std::cin.get(ch)) return curr_tok = END;
} while (ch!='\n' && isspace(ch));
switch (ch) {
case ';':
case '\n':
std::cin >> WS; // skip whitespace
return curr_tok=PRINT;
case '*':
case '/':
case '+':
case '-':
case '(':
case ')':
case '=':
return curr_tok=ch;
case '0': case '1': case '2': case '3': case '4': case '5':
case '6': case '7': case '8': case '9': case '.':
std::cin.putback(ch);
std::cin >> number_value;
return curr_tok=NUMBER;
default: // NAME, NAME=, or error
if (isalpha(ch)) {
char* p = name_string;
*p++ = ch;
while (std::cin.get(ch) && isalnum(ch)) *p++ = ch;
std::cin.putback(ch);
*p = 0;
return curr_tok=NAME;
}
error("bad token");
return curr_tok=PRINT;
}
The error it's spitting out is this:
calc.cpp:42: error: invalid conversion from ‘char’ to ‘token_value’
token_value
is an enum that looks like:
enum token_value {
NAME, NUMBER, END,
PLUS='+', MINUS='-', MUL='*', DIV='/',
PRINT=';', ASSIGN='=', LP='(', RP=')'
};
token_value curr_tok;
My question is, how do I convert ch (from cin), to the associated enum value?
解决方案
You can't implicitly cast from char
to an enum
- you have to do it explicitly:
return curr_tok = static_cast<token_value> (ch);
But be careful! If none of your enum
values match your char
, then it'll be hard to use the result :)
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