字符串的最小字典值

当使用运算符 smallest string?

更具体地说，什么是比任何其他字符串更小的（使用

空字符串是所有字符串中“最小”的——也就是说，它比任何非空字符串都小。

§21.4.8.4 [字符串::op

template<class charT, class traits, class Allocator>
bool operator< (const basic_string<charT,traits,Allocator>& lhs,
                const basic_string<charT,traits,Allocator>& rhs) noexcept;

1 Returns: lhs.compare(rhs) < 0.

§21.4.7.9 [字符串::比较]：

int compare(const basic_string& str) const noexcept;

1 Effects：确定有效长度rlen的字符串到 比较最小的size() and str.size()。功能 然后通过调用比较两个字符串traits::compare(data(), str.data(), rlen).

2 Returns：如果结果为非零结果 比较非零。否则，返回一个值，如 表 72.

表 72 —compare() 结果

 Condition               Return Value
 size() < str.size()     < 0
 size() == str.size()    0
 size() > str.size()     > 0

For any comparison between an empty string e and a non-empty string ne, rlen is zero, in which case traits::compare() is specified to return zero^*. Hence, the result of e.compare(ne) is always less than zero per table 72, and e < ne is always true.

^* _{The compare() function of character traits is specified to return zero if "for each i in [0,n), X::eq(p[i],q[i]) is true" (§21.2.1 [char.traits.require], Table 62); when n == 0, the range is empty, and the condition is vacuously true.}