C++ Regex not matching with a token in string

Regex is not matching a token { in string –

string:

{ int b = 10; }

code:

            std::cout << std::regex_match(line, m, std::regex("\\{")) << std::endl;
            std::cout << std::regex_match(line, m, std::regex("([A-Za-z0-9_]+) ([\\{]+)")) << std::endl;
            std::cout << std::regex_match(line, m, std::regex("([\\{])")) << std::endl;
            std::cout << std::regex_match(line, m, std::regex("([\\{]\n)")) << std::endl;

output:

{ int b = 10; }
0
0
0
0

I can’t find what I’ve missed out.