How do I sort a string using a custom compare function in C ++?
I need to sort the characters of a string and have lower letters first. For example, after sorting, "acDbA" becomes "abcAD".
Below is the code:
bool compare(const char& c1, const char& c2) {
if (c1 >= 'A' && c1 <= 'Z' && c2 >= 'a' && c2 <= 'z') return false;
if (c2 >= 'A' && c2 <= 'Z' && c1 >= 'a' && c1 <= 'z') return true;
return c1<c2;
}
void sortLetters(string &letters) {
sort(letters.begin(), letters.end(), compare);
}
However, in Visual Studio I got:
'sort': no matching overloaded function found
'SortLetters::compare': non-standard syntax; use '&' to create a pointer to member
'void std::sort(_RanIt,_RanIt)': expects 2 arguments - 3 provided
How to create a custom comparison function to sort a string, I couldn't find examples on the internet with sorting strings.
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The above code just compiles when using a free function. In your case, you are using an object method that is not just being called.
You can pass a functor object or a lambda object. By the way, since std :: sort is a function template, it doesn't matter what the exact parameters of the comparator are. The only thing that matters is that it can take both values and return something that can be converted to bool.
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The code below works, only change - the compare item function is now marked as "static":
class SortLetters {
public:
static bool compare(const char& c1, const char& c2) {
if (c1 >= 'A' && c1 <= 'Z' && c2 >= 'a' && c2 <= 'z') return false;
if (c2 >= 'A' && c2 <= 'Z' && c1 >= 'a' && c1 <= 'z') return true;
return c1<c2;
}
void sortLetters(string &letters) {
sort(letters.begin(), letters.end(), compare);
}
};
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