The pattern “(?<=aa)b” works, while “(?<=a{2})b” does not

[Viorel]

It seems that (?<=a{2})b is not accepted:

// Using CTRE 3.11.0,
// Visual Studio 2026, Console Application, C++20

#include "single-header\\ctre-unicode.hpp"

int main( )
{
	auto matches = ctre::search_all<L"(?<=a{2})b">( L"aab" );

	for( const auto& match : matches )
	{

	}

	return 0;
}

The errors are located in ctre-unicode.hpp:

• 'first': no matching overloaded function found
• 'collides': no matching overloaded function found
• binary '=': no operator found which takes a right-hand operand of type 'Iterator' (or there is no acceptable conversion)

If the pattern is replaced with a similar one — (?<=aa)b — then it works.

It is expected to work in both cases.

There is also an on-line sample for different compilers: https://godbolt.org/z/frTKGx4c8.