STL数组和com数组相互转换的做法

作者：朱金灿

来源：http://blog.csdn.net/clever101

STL的泛型数组是vetor，com的泛型数组类型是VARIANT。二者怎样能相互转化呢？就是说怎么把一个vector对象封装进VARIANT对象，又怎么将VARIANT对象封装进vector对象。经过一番研究，找到了办法。需要注意的是，数值数组和字符串数组是需要单独处理的。首先谈谈数组类型的数组如何转换，比如std::vector<int>转换为一个VARIANT对象。需要一个模板类来实现，代码如下：

template<class T>
class CVariantPack
{
private:

CVariantPack(void){};

~CVariantPack(void){};

public:

static bool SetTPtrVariant(VARENUM ElementType,const std::vector<T>& vecData,VARIANT &vdata)
{
try
{
if(vecData.empty())
{
return false;
}
SAFEARRAYBOUND rgsabound[1];
rgsabound[0].lLbound = 0;
rgsabound[0].cElements = (ULONG)vecData.size();

SAFEARRAY *psa = SafeArrayCreate(ElementType,1, rgsabound );
if( psa )
{
for( long i=0; i<(long)vecData.size(); i++ )
{
SafeArrayPutElement( psa, &i, (void *)(&vecData[i]));
}
vdata.vt = VT_ARRAY|ElementType;
vdata.parray = psa;
SafeArrayUnaccessData( psa );
return true;
}
else
{
return false;
}
}
catch(...)
{
return false;
}
}

static int GetTPtrVariant (VARENUM ElementType,std::vector<T>& vecData,const VARIANT vdata)
{
try
{
if( vdata.vt==VT_NULL || vdata.vt==VT_EMPTY )
{
return -1;
}
if( !(vdata.vt & VT_ARRAY)  )
{
return -2;
}
SAFEARRAY *psa = vdata.parray;
UINT nDims = SafeArrayGetDim( psa );
if( nDims != 1 )
{
return -3;
}
//检查数组元素类型
VARTYPE vt = 0;
SafeArrayGetVartype( psa, &vt );
if( vt != ElementType )
{
return -4;
}
//检查数组上下限和元素个数是否为偶数个
LONG lUBound =0, lLBound = 0;
SafeArrayGetUBound( psa, 1, &lUBound );
SafeArrayGetLBound( psa, 1, &lLBound );
int lElements = lUBound - lLBound + 1;
if( lElements <= 0 )
{
return -5;
}
T *pTmp = NULL;
SafeArrayAccessData( psa, (void **)&pTmp );
if( NULL == pTmp )
{
return -6;
}
for (int i = 0;i<lElements;i++)
{
vecData.push_back(*(pTmp+i));
}

SafeArrayUnaccessData( psa );
return lElements;
}
catch(...)
{
return -1;
};
}

};

测试函数如下：

bool TestVariantPack1(void)
{
std::vector<long> a;
a.push_back(1);
a.push_back(2);
a.push_back(3);
VARIANT vdata;
//long 数组封装到variant
if( !CVariantPack<long>::packtptrvariant(v_long,a,3,vdata))
{
return false;
}
std::vector<long> b;
//从variant获取long数组数据
int num= CVariantPack<long>::GetTPtrVariant(VT_I4,b,vdata);
if( num<=0 )
{
return false;
}
}

下面再谈谈字符串数组的相互转换。

// std::vector< std::wstring>转换为一个VARIANT对象
bool StringArrayToVariant(const std::vector< std::wstring >& vecData,VARIANT& vdata)
{
if(vecData.empty())
{
return false;
}

SAFEARRAY *psa;
SAFEARRAYBOUND rgsabound;
rgsabound.cElements = (ULONG)vecData.size();
rgsabound.lLbound = 0;
psa = SafeArrayCreate(VT_BSTR, 1, &rgsabound);//设置为一位BSTR数组
if( psa )
{
BSTR* bstrArray;
::SafeArrayAccessData(psa,(void**)&bstrArray);//将数据引出进行操作，并加锁
for (int i = 0 ; i < vecData.size(); ++i)
{
// bstrArray[i] =  arExport[i].AllocSysString(); // 如果是std::vector<CString>，请用这句代码
bstrArray[i] =  const_cast<TCHAR*>(vecData[i].c_str());
}

vdata.vt = VT_ARRAY|VT_BSTR;
vdata.parray = psa;
::SafeArrayUnaccessData(psa);
return true;
}
return false;
}

//VARIANT对象转换为std::vector< std::wstring>
int VariantToStringArray(const VARIANT& vdata,std::vector<std::wstring >& vecData)
{
if( vdata.vt==VT_NULL || vdata.vt==VT_EMPTY )
{
return -1;
}
if( !(vdata.vt & VT_ARRAY)  )
{
return -2;
}
SAFEARRAY *psa = vdata.parray;
UINT nDims = SafeArrayGetDim( psa );
if( nDims != 1 )
{
return -3;
}
//检查数组元素类型
VARTYPE vt = 0;
SafeArrayGetVartype( psa, &vt );
if( vt != VT_BSTR )
{
return -4;
}
//检查数组上下限和元素个数是否为偶数个
LONG lUBound =0, lLBound = 0;
SafeArrayGetUBound( psa, 1, &lUBound );
SafeArrayGetLBound( psa, 1, &lLBound );
int lElements = lUBound - lLBound + 1;
if( lElements <= 0 )
{
return -5;
}
BSTR* pTmp = NULL;
SafeArrayAccessData( psa, (void **)&pTmp );
if( NULL == pTmp )
{
return -6;
}
for (int i = 0;i<lElements;i++)
{
vecData.push_back(*(pTmp+i));
}

SafeArrayUnaccessData( psa );
return lElements;
}

这里需要注意的是，com只支持unicode字符，所以对应的stl字符串数组类型为std::vector<std::wstring>。

测试函数如下：

bool TestVariantPack(void)
{
std::vector<std::wstring> vecString;
vecString.push_back(_T("HelloWorld"));
vecString.push_back(_T(","));
vecString.push_back(_T("I am from China!"));

VARIANT vdata;
// std::vector<std::wstring> 数组封装到variant
if( !SysUtility::StringArrayToVariant(vecString,vdata))
{
return false;
}
std::vector<std::wstring> vecString2;
//从variant获取std::vector<std::wstring>数组数据
int num= SysUtility::VariantToStringArray(vdata,vecString2);
if( num<=0 )
{
return false;
}
return true;
}

参考文献：

1. 关于在C#中调用MFC编写Activex控件中传入字符串数组的有关问题