C++ 对字符串使用小于比较运算符
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Using the less than comparison operator for strings
提问by Dmist
I'm following a tutorial for C++ and looking at strings and overloading with operators such as +=, ==, != etc, currently have a simple if statement
我正在关注 C++ 的教程，并查看字符串和使用 +=、==、!= 等运算符重载，目前有一个简单的 if 语句
if(s1 < s2)
cout << s2 <<endl;
else
if(s2 < s1)
cout << s1 << endl;
else
cout << "Equal\n";
but how does this work, and how does the program decide which string is greater than another? looking around I've found a basic template decleration:
但是这是如何工作的，程序如何决定哪个字符串大于另一个？环顾四周，我发现了一个基本的模板声明：
template<class charT, class traits, class Allocator>
bool operator< ( const basic_string<charT,traits,Allocator>& lhs,
const basic_string<charT,traits,Allocator>& rhs );
does this define how < works? if so, what does mean / do?
这是否定义了 < 的工作原理？如果是这样，是什么意思/做什么？
also do the following operators have any meaning for strings? -= and *=
以下运算符对字符串也有任何意义吗？-= 和 *=
any advice is greatly appreciated!
任何意见是极大的赞赏！
回答by templatetypedef
The less-than operator on strings does a lexicographical comparison on the strings. This compares strings in the same way that they would be listed in dictionary order, generalized to work for strings with non-letter characters.
字符串上的小于运算符对字符串进行字典序比较。这以与按字典顺序列出的方式相同的方式比较字符串，概括为适用于具有非字母字符的字符串。
For example:
例如：
"a" < "b"
"a" < "ab"
"A" < "a" (Since A has ASCII value 65; a has a higher ASCII value)
"cat" < "caterpillar"
For more information, look at the std::lexicographical_comparealgorithm, which the less-than operator usually invokes.
有关更多信息，请查看std::lexicographical_compare小于运算符通常调用的算法。
As for -=and *=, neither of these operators are defined on strings. The only "arithmetic" operators defined are +and +=, which perform string concatenation.
至于-=and *=，这两个运算符都没有在字符串上定义。定义的唯一“算术”运算符是+and +=，它们执行字符串连接。
Hope this helps!
希望这可以帮助！
回答by NPE
The comparison operators implement lexicographic orderingof strings.
比较运算符实现字符串的字典顺序。
-=and *=are not defined for strings.
-=并且*=不是为字符串定义的。
