C++ 按字典序比较字符串
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Comparing strings lexicographically
提问by slugo
I thought that if I used operators such as ">" and "<" in c++ to compare strings, these would compare them lexicographically, the problem is that this only works sometimes in my computer. For example
我想如果我在 c++ 中使用诸如“>”和“<”之类的运算符来比较字符串，它们会按字典顺序比较它们，问题是这只在我的计算机中有时有效。例如
if("aa" > "bz") cout<<"Yes";
This will print nothing, and thats what I need, but If I type
这不会打印任何内容，这就是我需要的，但是如果我输入
if("aa" > "bzaa") cout<<"Yes";
This will print "Yes", why is this happening? Or is there some other way I should use to compare strings lexicographically?
这将打印“是”，为什么会发生这种情况？或者我应该使用其他方法来按字典顺序比较字符串吗？
回答by Ivaylo Strandjev
Comparing std::string-s like that willwork. However you are comparing string literals. To do the comparison you want either initialize a std::string with them or use strcmp:
std::string像这样比较-s会起作用。但是，您正在比较字符串文字。要进行比较，您需要使用它们初始化 std::string 或使用 strcmp：
if(std::string("aa") > std::string("bz")) cout<<"Yes";
This is the c++ style solution to that.
这是 C++ 风格的解决方案。
Or alternatively:
或者：
if(strcmp("aa", "bz") > 0) cout<<"Yes";
EDIT(thanks to Konrad Rudolph's comment): in fact in the first version only one of the operands should be converted explicitly so:
编辑（感谢 Konrad Rudolph 的评论）：实际上，在第一个版本中，只有一个操作数应该显式转换，因此：
if(std::string("aa") > "bz") cout<<"Yes";
Will again work as expected.
将再次按预期工作。
回答by nobar
You are comparing "primitive" strings, which are of type char const *.
您正在比较类型为 的“原始”字符串char const *。
The following is essentially equivalent to your example:
以下内容基本上等同于您的示例：
char const * s1 = "aa";
char const * s2 = "bz";
if ( s1 > s2 ) cout<<"Yes";
This is comparing the pointers (the memory addresses of the strings), not the contents.
这是比较指针（字符串的内存地址），而不是内容。
@izomorphius has suggested some good solutions.
@izomorphius 提出了一些很好的解决方案。
