std::stringstream sstream;
sstream << R"(
<array>
  <item>
    <string>foo</string>
    <bool>true</bool>
  </item>
  <item>
    <string>bar</string>
    <bool>false</bool>
    <float>0.4</float>
  </item>
  <item>
    <string>test</string>
    <bool>false</bool>
  </item>
</array>
)";

Poco::XML::InputSource src(sstream);
Poco::XML::DOMParser parser;
auto doc = parser.parse(&src);

auto node = doc->getNodeByPath("/array/item[0]/float");
std::cout << (node ? node->innerText() : "[not found]") << std::endl;

node = doc->getNodeByPath("/array/item[1]/float");
std::cout << (node ? node->innerText() : "[not found]") << std::endl;

node = doc->getNodeByPath("/array/item[2]/float");
std::cout << (node ? node->innerText() : "[not found]") << std::endl;