C++ std::find for strings ignoreres lower/upper case?

Question

I need for a class a function which checks if a string is contained in another. Did I understand right that the STL function std::find for strings ignore lower and upper case (that is what I need)?

Use `std::find_if` instead and supply a function to do the case insensitive comparison. — john, Jul 20 '20 at 09:23
your question is kind of vague, what exactly are you tryinjg to do? — Adrian Costin, Jul 20 '20 at 09:26
To use @john solution this thread may help https://stackoverflow.com/q/36494584/6865932 — anastaciu, Jul 20 '20 at 09:27
In recommend you to provide full description of your problem, to avoid misunderstanding. Issue can be more complex then you can imagine, for example if your string is UTF-8 encoded. — Marek R, Jul 20 '20 at 09:38

Adrian Costin · Accepted Answer · 2020-07-20T10:58:03.270

2

find searches for an element equal to value

std::string::find iterates over the range and returns the position to the first element satisfying the condition or last is no match was found.

if you pass a substring contained in a larger string to the std::find function, the algorithm should return the position where the substring starts.

std::string::find is not case insensitive, it just iterates the container and checks if the substring is present

edited Jul 20 '20 at 10:58

answered Jul 20 '20 at 09:25

Adrian Costin

418
3
12

1

`std::find` returns an iterator and finds characters in strings, not substrings. Maybe you refer to `std::string::find`(but that also returns no pointer) – 463035818_is_not_an_ai Jul 20 '20 at 09:50
1

also not an iterator to the last element is returned, but an iterator one past the last element if the element could not be found – 463035818_is_not_an_ai Jul 20 '20 at 09:51
yes, it returns std::string::npos, and yes it is std::string::find @idclev463035818, thank you for the correction. aren't iterators just a generalization of pointers though ? – Adrian Costin Jul 20 '20 at 10:57
vehicle is a generalization for car, but yet planes are no cars ;) – 463035818_is_not_an_ai Jul 20 '20 at 11:30

score 1 · Answer 2 · answered Jul 20 '20 at 11:17

std::string::find does not perform a case-insensitive search; it searches for an exact match. You would have to convert both the string to search and the search term to either lower or upper case first, and then use std::string::find.

However, there is another way you could do it with modern C++ (C++11 onward): use std::regex_search with the std::regex_constants::icase flag:

bool findCaseInsensitiveRegex(const std::string &completeString, const std::string &toSearch)
{
    std::regex pattern(toSearch, std::regex_constants::icase);
    return std::regex_search(completeString, pattern);
}

where toSearch is a regex made from the string to search for, and completeString is the complete string to search in.

Examples of both methods here.

C++ std::find for strings ignoreres lower/upper case?

2 Answers2