WKB hex decoder in C++
In PostGIS world, I often need to construct geometry from Well-Known-Binary (WKB) or PostGIS EWKB stream encoded as hex stream. It’s easy to do if I have access to PostgreSQL/PostGIS client which accepts SQL queries:
SELECT
ST_AsText(
ST_GeomFromWKB(
decode('0101000000e5d022dbf93e2e40dbf97e6abc743540', 'hex'),
4326))I often need to do the same directly in C++ code - parse hex encoded binary stream to raw stream of bytes. Here is simple hex decoder I use:
#include <sstream>
#include <string>
#include <vector>
typedef std::vector<unsigned char> ewkb_t;
void hex_to_bytes(std::string const& hexstr, ewkb_t bytes)
{
bytes.clear();
for(std::string::size_type i = 0; i < hexstr.size() / 2; ++i)
{
std::istringstream iss(hexstr.substr(i * 2, 2));
unsigned int n;
iss >> std::hex >> n;
bytes.push_back(static_cast<unsigned char>(n));
}
}
For example, I use it to build FDO geometry objects using another utility CreateGeometryFromExtendedWkb defined in FDO provider for PostGIS:
// POINT (1.234 5.678)
std::string ewkbhex("01010000005839B4C876BEF33F83C0CAA145B61640");
ewkb_t ewkb;
hex_to_bytes(ewkbhex, ewkb);
if (!ewkb.empty())
{
FdoPtr<fdoigeometry> g = CreateGeometryFromExtendedWkb(ewkb);
// ... use geometry
}