ylbtech-Docs-.NET-C # - guide - Language Reference - preprocessor directives: #define (C # Reference)

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#define (C # Reference)

2018/06/30

Used #define to define the symbol. The symbols are used to pass #if when the command expression, the calculation result of the expression is true , as shown in the following example:

#define DEBUG

Remark

#define Instruction can not be used to declare a constant value, as in the C and C ++ usual practice. C # constants is best defined as a static class member, or structure. If you have more than one such constants, consider creating a separate "constant" classes to accommodate them.

Symbols can be used to specify conditional compilation. By #if or #elif test symbols. You can also use ConditionalAttribute to perform conditional compilation.

You can define a symbol, but not the value of the symbol allocation. The documentation must appear first #define instruction, not to use any instructions but also the preprocessor directives.

Can also -define to define the symbol compiler option. By #undef canceled defined symbols.

Use -define or #define symbol defined variable with the same name does not conflict. That is, the variable name should not be passed to the pre-processor instructions, and the symbol can only be evaluated by pre-processor instructions.

Use #define symbols created in which a scope is defined in the symbol file.

As shown in the following example, you must be #define the instruction at the top of the file.

#define DEBUG  
//#define TRACE  
#undef TRACE  
  
using System;  
  
public class TestDefine  
{  
    static void Main()  
    {  
#if (DEBUG)  
        Console.WriteLine("Debugging is enabled.");  
#endif  
  
#if (TRACE)  
     Console.WriteLine("Tracing is enabled.");  
#endif  
    }  
}  
// Output:  
// Debugging is enabled.

For information about how to cancel an example of the symbol is defined, see #undef .

See

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https://docs.microsoft.com/zh-cn/dotnet/csharp/language-reference/preprocessor-directives/preprocessor-define

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Author: ylbtech
Source: http://ylbtech.cnblogs.com/
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Docs-.NET-C # - guide - Language Reference - preprocessor directives: #define (C # Reference)

#define (C # Reference)

Remark

See

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