fRead (Function)

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Ayuda / WLanguage / Funciones WLanguage / Funciones estándar / Funciones de archivos externos

Handling errors
Position in the file

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fRead (Function)

Reads a block of bytes in an external file.

In this version, you can only read a character string from an external file in ANSI format.

Ejemplo

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// Open an external file
FileID is int
ResRead is int
FileID = fOpen("C:\MyDirectories\File.txt", foReadWrite)
IF FileID <> -1 THEN
	// Read operation in this file
	ResRead = fRead(FileID, 200)
	...
END

// Open an external file
MyTextFile is DiskFile
ResRead is int
MyTextFile = fOpen("C:\MyDirectories\File.txt", foReadWrite)
IF NOT ErrorOccurred THEN
	// Read operation in this file
	ResRead = fRead(MyTextFile, 200)
	...
END

Sintaxis

Reading a block of bytes in an external file Ocultar los detalles

<Result> = fRead(<File used> , <Number of bytes to read>)

<Result>: Character string

Block of bytes that was read.
Empty string ("") if an error occurred. To get more details on the error, use ErrorInfo with the errMessage constant.

<File used>: Integer or DiskFile variable

Identifier of the file to use, defined by fOpen or fCreate.
Name of variable of type DiskFile initialized with function fOpen or fCreate.
Not available.

<Number of bytes to read>: Integer

Number of bytes to read (up to 2 147 483 648 bytes).
If the data is a Unicode string, the number of bytes to read corresponds to:
in UTF16: the number of characters multiplied by 2.
in UTF32: the number of characters multiplied by 4.

Reading the content of an external file and assigning it to a memory area (identified by its address) Ocultar los detalles

<Result> = fRead(<File used> , <Number of bytes to read> , <Address>)

<Result>: Integer

Number of bytes read,
0 if an error occurs. To get more details on the error, use ErrorInfo with the errMessage constant.

<File used>: Integer or DiskFile variable

Identifier of the file to use, defined by fOpen or fCreate.
Name of the DiskFile variable initialized with fOpen or fCreate.

<Number of bytes to read>: Integer

Number of bytes to read (up to 2 147 483 648 bytes).
If the data is a Unicode string, the number of bytes to read corresponds to:
in UTF16: the number of characters multiplied by 2.
in UTF32: the number of characters multiplied by 4.

<Address>: Address

Address of affected memory section.

Observaciones

Handling errors

fRead throws an error in the following cases:

the file is not opened,
the file is not accessible in read mode,
the file is locked by another computer or by another application,
the end of the file has been reached.

Position in the file

When opening a file, the current position corresponds to:

the first file byte (by default),
the last byte of the file is the file is opened in "addition" mode (foAdd constant).

This position can be modified by fSeek.

fRead reads the specified elements from the current position. Once fRead has been executed, the current position is set to the last byte read.

Note: To always read the beginning of the file, use the fSeek function followed by the fReadfunction. .

Clasificación Lógica de negocio / UI: Lógica de negocio

Componente: wd300std.dll

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Versión mínima requerida

Versión 9

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Última modificación: 28/03/2025

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