c++读取shape文件中的线和面代码

读取shape文件可以使用开源库GDAL（Geospatial Data Abstraction Library），GDAL支持读取shape文件并提供了丰富的API。

以下是使用GDAL读取shape文件中线和面的示例代码：

#include "gdal_priv.h"
#include "ogr_api.h"
#include "ogr_geometry.h"

int main()
{
    // 打开shape文件
    GDALAllRegister();
    GDALDataset* poDS = (GDALDataset*)GDALOpenEx("path/to/shapefile.shp", GDAL_OF_VECTOR, NULL, NULL, NULL);

    // 获取图层
    OGRLayer* poLayer = poDS->GetLayer(0);

    // 读取线
    poLayer->ResetReading();
    OGRFeature* poFeature = poLayer->GetNextFeature();
    while(poFeature)
    {
        OGRGeometry* poGeometry = poFeature->GetGeometryRef();
        if(poGeometry->getGeometryType() == wkbLineString)
        {
            OGRLineString* poLine = (OGRLineString*)poGeometry;
            int nPoints = poLine->getNumPoints();
            for(int i = 0; i < nPoints; i++)
            {
                double x = poLine->getX(i);
                double y = poLine->getY(i);
                // 处理线上的点
            }
        }
        poFeature->Destroy();
        poFeature = poLayer->GetNextFeature();
    }

    // 读取面
    poLayer->ResetReading();
    poFeature = poLayer->GetNextFeature();
    while(poFeature)
    {
        OGRGeometry* poGeometry = poFeature->GetGeometryRef();
        if(poGeometry->getGeometryType() == wkbPolygon)
        {
            OGRPolygon* poPolygon = (OGRPolygon*)poGeometry;
            int nRings = poPolygon->getNumInteriorRings() + 1;
            for(int i = 0; i < nRings; i++)
            {
                OGRLinearRing* poRing = i == 0 ? poPolygon->getExteriorRing() : poPolygon->getInteriorRing(i - 1);
                int nPoints = poRing->getNumPoints();
                for(int j = 0; j < nPoints; j++)
                {
                    double x = poRing->getX(j);
                    double y = poRing->getY(j);
                    // 处理面上的点
                }
            }
        }
        poFeature->Destroy();
        poFeature = poLayer->GetNextFeature();
    }

    // 关闭文件
    GDALClose(poDS);

    return 0;
}

这段代码可以读取shape文件中的第一个图层（如果有多个图层，可以使用GetLayer(i)获取第i个图层），并分别读取线和面上的点。需要注意的是，读取面时需要分别处理面的外环和内环。