CODEWITHSUNDEEP
c++regex
dexylitol
dexylitol

Reputation: 41

c++ std::regex doesn't match as expected

I've tried to implement a simple string-test method using c++ std::regex, in MS VC++ 2012.

const std::string str = "1.0.0.0029.443";

if ( std::regex_match( str, std::regex( "\\.0\\d+" ) ) )
    std::cout << "matched." << std::endl;

I guessed that the code would match ".0029" part of the given str. However, it doesn't match at all. I tried it on http://regex101.com/ and it worked.

Upvotes: 2

Views: 1920

Answers (3)

hwnd
hwnd

Reputation: 70732

Use std::regex_search instead to return your submatch.

const std::string str = "1.0.0.0029.443";

std::regex rgx("(\\.0[0-9]+)");
std::smatch match;

if (std::regex_search(str.begin(), str.end(), match, rgx)) {
    std::cout << match[1] << '\n';
}

Upvotes: 4

zx81
zx81

Reputation: 41838

To ensure your regex matches the full string and nothing else, you need something like this:

^(?:\d+\.)*\d+$

This translates into 

if ( std::regex_match( str, std::regex( "^(?:\\d+\\.)*\\d+$" ) ) )
    std::cout << "matched." << std::endl;

The beginning and end of anchors ^ and $ are required, otherwise you might match a string in the middle of BANANA_0.1.12AND_APPLE

Upvotes: 0

T.C.
T.C.

Reputation: 137330

std::regex_match reports an exact match, i.e., the entire input string must match the regex.

To match subsequences, use std::regex_search.

Upvotes: 4

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