There is no way to change the precision via to_string()
but the setprecision IO manipulator could be used instead:
#include <sstream>
template <typename T>
std::string to_string_with_precision(const T a_value, const int n = 6)
{
std::ostringstream out;
out.precision(n);
out << std::fixed << a_value;
return out.str();
}