C++ regex_match not working

Question

Here is part of my code

bool CSettings::bParseLine ( const char* input )
{
    //_asm INT 3


    std::string line ( input );
    std::size_t position = std:         


        

Answer 1

The problem is that std::regex_match must match the entire string but you are trying to match only part of it.

You need to either use std::regex_search or alter your regular expression to match all three parts at once:

#include <regex>
#include <string>
#include <iostream>

const auto test =
{
      "foo.bar = 15"
    , "baz.asd = 13"
    , "ffffd.dgh = 66"
};

int main()
{
    const std::regex r(R"~(([^.]+)\.([^\s]+)[^0-9]+(\d+))~");
    //                     (  1  )  (   2  )       ( 3 ) <- capture groups

    std::cmatch m;

    for(const auto& line: test)
    {
        if(std::regex_match(line, m, r))
        {
            // m.str(0) is the entire matched string
            // m.str(1) is the 1st capture group
            // etc...
            std::cout << "a = " << m.str(1) << '\n';
            std::cout << "b = " << m.str(2) << '\n';
            std::cout << "c = " << m.str(3) << '\n';
            std::cout << '\n';
        }
    }
}

Regular expression: https://regex101.com/r/kB2cX3/2

Output:

a = foo
b = bar
c = 15

a = baz
b = asd
c = 13

a = ffffd
b = dgh
c = 66

Answer 2

To focus on regex patterns I'd prefer to use raw string literals in c++:

regex cvarPattern ( R"rgx(\.([a-zA-Z_]+))rgx" );
regex parentPattern ( R"rgx(^([a-zA-Z0-9_]+)\.)rgx" );
regex cvarValue ( R"rgx(\.[a-zA-Z0-9_]+[ ]*=[ ]*(\d+\.*\d*))rgx" );

Everything between the rgx( )rgx delimiters doesn't need any extra escaping for c++ char literal characters.

---

Actually what you have written in your question resembles to those regular expressions I've been writing as raw string literals.
You probably simply meant something like

regex cvarPattern ( R"rgx(.([a-zA-Z_]+))rgx" );
regex parentPattern ( R"rgx(^([a-zA-Z0-9_]+).)rgx" );
regex cvarValue ( R"rgx(.[a-zA-Z0-9_]+[ ]*=[ ]*(\d+(\.\d*)?))rgx" );

I didn't dig in deeper, but I'm not getting all of these escaped characters in your regular expression patterns now.

---

As for your question in the comment, you can use a choice of matching sub-pattern groups, and check for which of them was applied in the matches structure:

regex cvarValue ( 
   R"rgx(.[a-zA-Z0-9_]+[ ]*=[ ]*((\d+)|(\d+\.\d?)|([a-zA-Z]+)){1})rgx" );
                             // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

You probably don't need these cvarPattern and parentPattern regular expressions to inspect other (more detailed) views about the matching pattern.