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Source Line, File, and Path Identifiers

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The identifiers __LINE__, __SOURCE_DIRECTORY__ and __SOURCE_FILE__ are built-in values that enable you to access the source line number, directory and file name in your code.

Syntax

__LINE__
__SOURCE_DIRECTORY__
__SOURCE_FILE__

Remarks

Each of these values has type string.

The following table summarizes the source line, file, and path identifiers that are available in F#. These identifiers are not preprocessor macros; they are built-in values that are recognized by the compiler.

Predefined identifier Description
__LINE__ Evaluates to the current line number, considering #line directives.
__SOURCE_DIRECTORY__ Evaluates to the current full path of the source directory, considering #line directives.
__SOURCE_FILE__ Evaluates to the current source file name, without its path, considering #line directives.

For more information about the #line directive, see Compiler Directives.

Example

The following code example demonstrates the use of these values.

let printSourceLocation() =
    printfn "Line: %s" __LINE__
    printfn "Source Directory: %s" __SOURCE_DIRECTORY__
    printfn "Source File: %s" __SOURCE_FILE__
printSourceLocation()

Output:

Line: 4
Source Directory: C:\Users\username\Documents\Visual Studio 2017\Projects\SourceInfo\SourceInfo
Source File: Program.fs

See also