Method substring

Sming/Wiring/WString.cpp:775–786

}

String String::substring(size_t left, size_t right) const
{
	auto len = length();
	if(left > right || left >= len) {
		return nullptr;
	}

	if(right > len) {
		right = len;
	}
	return String(cbuffer() + left, right - left);
}

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/*  Modification                             */