我正在尝试公开需要从 GeoTrans c++ 库调用的方法，但遇到了问题。任何帮助都会很棒!

我有以下 c++ 文件，我正在运行 nmake 以将其编译成 dll。

#include <iostream>

#include "CoordinateConversionService.h"
#include "CoordinateSystemParameters.h"
#include "GeodeticParameters.h"
#include "CoordinateTuple.h"
#include "GeodeticCoordinates.h"
#include "CartesianCoordinates.h"
#include "Accuracy.h"
#include "MGRSorUSNGCoordinates.h"
#include "UTMParameters.h"
#include "UTMCoordinates.h"
#include "CoordinateType.h"
#include "HeightType.h"
#include "CoordinateConversionException.h"

using MSP::CCS::Precision;

int main(int argc, char **argv){}

extern "C"__declspec(dllexport) void __stdcall convertGeodeticToGeocentric(const double lat,const double lon, const double height, double& x, double& y, double& z)
{       
        MSP::CCS::CoordinateSystemParameters geocentricParameters(MSP::CCS::CoordinateType::geocentric);
        MSP::CCS::CoordinateConversionService ccs( "WGE", &geodeticParameters, "WGE", &geocentricParameters );
        MSP::CCS::Accuracy sourceAccuracy;
        MSP::CCS::Accuracy targetAccuracy;
        MSP::CCS::GeodeticCoordinates sourceCoordinates(MSP::CCS::CoordinateType::geodetic, lon, lat, height);
        MSP::CCS::CartesianCoordinates targetCoordinates(MSP::CCS::CoordinateType::geocentric);
        ccs.convertSourceToTarget( &sourceCoordinates, &sourceAccuracy, targetCoordinates, targetAccuracy );
        x = targetCoordinates.x();
        y = targetCoordinates.y();
        z = targetCoordinates.z();
}

extern "C"__declspec(dllexport) void __stdcall convertGeocentricToGeodetic(const double x, const double y, const double z, double& lat,double& lon, double& height)
{
        MSP::CCS::CoordinateSystemParameters geocentricParameters(MSP::CCS::CoordinateType::geocentric);
        MSP::CCS::GeodeticParameters geodeticParameters(MSP::CCS::CoordinateType::geodetic, MSP::CCS::HeightType::ellipsoidHeight);
        MSP::CCS::CoordinateConversionService ccs( "WGE", &geocentricParameters, "WGE", &geodeticParameters );
        MSP::CCS::Accuracy sourceAccuracy;
        MSP::CCS::Accuracy targetAccuracy;
        MSP::CCS::CartesianCoordinates sourceCoordinates(MSP::CCS::CoordinateType::geocentric, x, y, z);
        MSP::CCS::GeodeticCoordinates targetCoordinates;
        ccs.convertSourceToTarget( &sourceCoordinates, &sourceAccuracy, targetCoordinates, targetAccuracy );
        lat = targetCoordinates.latitude();
        lon = targetCoordinates.longitude();
        height = targetCoordinates.height();
}

extern "C"__declspec(dllexport) void __stdcall convertGeocentricToUTM(const double x, const double y, const double z, long& zone, char& hemisphere, double& easting, double& northing)
{
        MSP::CCS::CoordinateSystemParameters geocentricParameters(MSP::CCS::CoordinateType::geocentric);
        MSP::CCS::UTMParameters utmParameters(MSP::CCS::CoordinateType::universalTransverseMercator, 1, 0);
        MSP::CCS::CoordinateConversionService ccs( "WGE", &geocentricParameters, "WGE", &utmParameters );
        MSP::CCS::Accuracy sourceAccuracy;
        MSP::CCS::Accuracy targetAccuracy;
        MSP::CCS::CartesianCoordinates sourceCoordinates(MSP::CCS::CoordinateType::geocentric, x, y, z);
        MSP::CCS::UTMCoordinates targetCoordinates;
        ccs.convertSourceToTarget( &sourceCoordinates, &sourceAccuracy, targetCoordinates, targetAccuracy );
        zone = targetCoordinates.zone();
        hemisphere = targetCoordinates.hemisphere();
        easting = targetCoordinates.easting();
        northing = targetCoordinates.northing();
}

extern "C"__declspec(dllexport) void __stdcall convertGeocentricToMGRS(const double x, const double y, const double z, char*& mgrsString, Precision::Enum& precision)
{
        MSP::CCS::CoordinateSystemParameters geocentricParameters(MSP::CCS::CoordinateType::geocentric);
        MSP::CCS::CoordinateSystemParameters mgrsParameters(MSP::CCS::CoordinateType::militaryGridReferenceSystem);
        MSP::CCS::CoordinateConversionService ccs( "WGE", &geocentricParameters, "WGE", &mgrsParameters );
        MSP::CCS::Accuracy sourceAccuracy;
        MSP::CCS::Accuracy targetAccuracy;
        MSP::CCS::CartesianCoordinates sourceCoordinates(MSP::CCS::CoordinateType::geocentric, x, y, z);
        MSP::CCS::MGRSorUSNGCoordinates targetCoordinates;
        ccs.convertSourceToTarget( &sourceCoordinates, &sourceAccuracy, targetCoordinates, targetAccuracy );
        mgrsString = targetCoordinates.MGRSString();
        precision = targetCoordinates.precision();
}

然后我在我的 C# 类中有以下 p/invoke 调用..

[DllImport("CoordinateConversionWrapper.dll")]
private static extern void convertGeodeticToGeocentric(double lat, double lon, double height, ref double x, ref double y, ref double z);

[DllImport("CoordinateConversionWrapper.dll")]
private static extern void convertGeocentricToMGRS(double x, double y, double z, ref char[] mgrsString, Precision precision);

调用上述任何 p/invoke 方法都会导致 NullReferenceException。看起来问题出在 c++ 代码本身，但不是 c++ 专家我不确定问题是什么......

请帮忙!!

最佳答案

我建议调试您的代码。您可以在 C# 项目的设置(“调试”选项卡)中启用调试非托管代码。

请同时发布调用代码。

备注:p/invoke 的字符串输出参数通常由 StringBuilder 类完成。

[编辑] 字符串输出有问题 - 谁为字符串提供存储空间以及谁释放它(如果需要)？唯一有用的解决方案是将存储(作为 char*)及其长度传递给 C++ 函数。如前所述，在 C# 端使用 StringBuilder。

关于.net - GeoTrans p/调用包装器 NullReferenceException，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/7052126/