How to use the COleVariant class in MFC?

2 years ago
Noah Thompson
2 minutes

The COleVariant class in MFC is used to encapsulate the VARIANT data type, making it very useful when working with COM objects and handling OLE Automation interfaces. Here are the ways to use the COleVariant class:

  1. Include header file
    Before using the COleVariant class, you need to include the afxdisp.h header file in the source file.
  2. Creating a COleVariant object
    A COleVariant object can be created using different forms of overloaded constructors. Users can choose the appropriate constructor based on their needs. For example:
COleVariant var; // 默认构造函数
COleVariant var(10); // 根据整型值构造
COleVariant var("Hello"); // 根据字符串构造
COleVariant var(date); // 根据日期构造
// ...
  1. Assign a value to the COleVariant object by using one of the various available functions in the COleVariant class. Choose the appropriate function based on your requirements. For example:
var = 10; // 设置整型值
var = "Hello"; // 设置字符串值
var = date; // 设置日期值
var.ChangeType(VT_BOOL); // 设置变量类型为布尔型
// ...
  1. Obtaining the value of a COleVariant object can be done using various functions provided by the COleVariant class. Choose the appropriate function based on your needs. For example:
int nValue = var.intVal; // 获取整型值
CString strValue = var.bstrVal; // 获取字符串值
COleDateTime dateValue = var.date; // 获取日期值
BOOL bValue = var.boolVal; // 获取布尔值
// ...
  1. Determine the type of COleVariant object
    The COleVariant class provides a function GetType() to retrieve the data type of the COleVariant object. For example:
VARTYPE type = var.GetType(); // 获取对象的数据类型
if (type == VT_I4) {
    // 对象类型为整型
}
else if (type == VT_BSTR) {
    // 对象类型为字符串
}
// ...

These are the basic uses of the COleVariant class, which makes it easy to manipulate data of VARIANT type.

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