C规范(6.7.2.2)的枚举特定部分规定：
The identifiers in an enumerator list are declared as constants that have type int and
may appear wherever such are permitted.127) An enumerator with = defines its
enumeration constant as the value of the constant expression. If the first enumerator has
no =,the value of its enumeration constant is 0.
所以我应该能够使用与int常量相同的枚举成员.在这个小样本程序中：
enum first {
a,b
};
enum second {
c,d
};
int main(){
enum first myf = a;
enum second mys = c;
if(myf == mys)
printf("same value\n");
return 0;
}
当编译gcc -Wall -Werror时,我收到消息：
error: comparison between ‘enum first’ and ‘enum second’ [-Werror=enum-compare]
我知道,如果我将myf和MysqL的类型转换为int,那么编译器将会很开心,就像我可以用myf和mys的值来设置几个int,并进行比较;但为什么我要做这些任何一个来摆脱警告呢？为什么首先存在这个警告？这样做,我看不到会有一些危险.
注意：我已经阅读了关于这个枚举比较标志的gcc文档,但它并没有说什么：
-Wenum-compare
Warn about a comparison between values of different enumerated types. In C++ enumeral mismatches in conditional expressions are also diagnosed and the warning is enabled by default. In C this warning is enabled by -Wall.
解决方法
enum Day {
Sunday,Monday,Tuesday,Wednesday,Thursday,Friday,Saturday
};
enum Month {
January,February,March,April,May,June,July,August,September,October,November,December
};
enum Day day = Wednesday;
enum Month month = April;
if (day == month) { ... }
这个评估是真实的,但总体上来说,这种比较并没有多大意义.如果你知道你的意思,那么typecast会说服编译器,正如你所说.
