用gdal打开一个shp文件并读出里面点的坐标，并计算面积。

#include
#include<stdlib.h>
#include
#include
#include
#include"ogrsf_frmts.h"
using namespace std;
extern double getarea(OGRLinearRing *ring);
int main()
{
GDALAllRegister();
GDALDataset lauds;
lauds = (GDALDataset)GDALOpenEx(“E:/Desktop/national fundamental information/LanduseData/LanduseData/Landuse.shp”, GDAL_OF_VECTOR||GDAL_OF_UPDATE, NULL, NULL, NULL);

if (lauds == NULL)
{
	cout << "open failed\n" << endl;
	exit(1);
}

OGRLayer *laulayer;
laulayer = lauds->GetLayerByName("Landuse");
//laulayer->DeleteField(5);

#if 0
OGRFieldDefn ofield(“area_sum”, OFTReal);
if (laulayer->CreateField(&ofield, TRUE) != OGRERR_NONE)
{
cout << “Creating Name field failed.\n” << endl;
}
#endif

OGRFeature *laufeature;
laulayer->ResetReading();
while ((laufeature=laulayer->GetNextFeature())!=NULL)
{