如何在C ++中比较base36值？

Question

As we all know, with C-style string comparisons, the value is dependent on the ASCII value of each character and just uses the strcmp function to compare. I'm confused that what the std::string compare depends on?

Although I have searched Google, I still didn't find the answer.

In addition, if strings are all base36 strings and they are all in lower case, could I compare their values by strings directly? Or I should convert them as a long variable using the strtol function? Which method is better?

Answer 1

Your outset "As we all know, with C-style string comparisons, the value is dependent on the ASCII value of each character..." is unfortunately wrong already. With eg UTF-8 strings and various forms of collation, that's simply untrue.

Then "...and just uses the strcmp function to compare." is also wrong, because C-style strings don't have an inherent way to compare but multiple ways that also depend on eg the encoding and locale. You could use strcmp() for bytewise equality comparisons though, but that won't always give you expected results.

To answer your question what std::string uses, that's simple. std::string is a specialization of the std::basic_string template and it delegates comparisons to its char_traits template parameter. This parameter typically uses memcmp() . It can not possibly use strcmp() , because other than a C-style string, std::string can include null chars, but strcmp() would stop at those.

Answer 2

std::string compare depends upon 'ASCII values' in exactly the same way that strcmp does.

For base36 comparisons, simple string comparison (either strcmp or std::string) doesn't work because "00123" and "123" are equal when representing base36 integers but they compare differently as strings. Neither does strtol work very well because of integer overflow. Instead you should probably write your own comparison routine that removes leading zeros, then compares length and finally for strings of equal length does a string comparison.