Option Strict on Option Explicit On

偏执的太偏执、 2021-12-15 08:57 234阅读 0赞

**Option Strict on**

Visual Basic .NET generally allows implicit conversions of any data type to any other data type. Data loss can occur when the value of one data type is converted to a data type with less precision or smaller capacity, however, a run-time error message will occur if data will be lost in such a conversion. **Option Strict** ensures compile-time notification of these types of conversions so they may be avoided.

In addition to disallowing narrowing conversions, **Option Strict** generates an error for *late binding.* An object is late bound when it is assigned to a variable that is declared to be of type Object.

> **Note** The compiler default is **Option Strict Off** if do not specify **Option Strict** in your code.  
>   
> 
> 
> #### Example ####
> 
> This example demonstrates how the **Option** **Strict** statement disallows late binding and conversions where data would be lost.
> 
>     Option Strict On   ' Force explicit variable declaration.
>     
>     Dim MyVar As Integer   ' Declare variables.
>     Dim Obj As Object
>     
>     MyVar = 1000   ' Declared variable does not generate error.
>     
>     'Attempting to convert to an Integer generates an error.
>     MyVar = 1234567890.987654321
>     '
>     'Call Obj.Method1()   ' Late-bound call generates an error
>     
>     
>     
>     
>     Option Explicit On
> 
> #### Remarks ####
> 
> If used, the **Option** **Explicit** statement must appear in a file before any other source statements.
> 
> When **Option Explicit** appears in a file, you must explicitly declare all variables using the **Dim**, **Private**, **Public**, or **ReDim** statements. If you attempt to use an undeclared variable name, an error occurs at compile time.
> 
> If you don't use the **Option Explicit** statement, all undeclared variables are of **Object** type.
> 
> > **Note** Use **Option Explicit** to avoid incorrectly typing the name of an existing variable or to avoid confusion in code where the scope of the variable is not clear. If you do not specify **Option Explicit** in your code, the compiler default is **Option Explicit On**.
> 
> #### Example ####
> 
> This example uses the **Option Explicit** statement to force explicit declaration of all variables. Attempting to use an undeclared variable causes an error at compile time. The **Option Explicit** statement is used at the module level only.
> 
>     Option Explicit On   ' Force explicit variable declaration.
>     Dim MyVar As Integer   ' Declare variable.
>     MyInt = 10   ' Undeclared variable generates error.
>     MyVar = 10   ' Declared variable does not generate error.

转载于:https://www.cnblogs.com/yangbin990/archive/2005/11/30/287445.html