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Put statement

  • Cikk

Writes data from a variable to a disk file.

Syntax

Put [ # ] filenumber, [ recnumber ], varname

The Put statement syntax has these parts:

Part Description
filenumber Required. Any valid file number.
recnumber Optional. Variant (Long). Record number (Random mode files) or byte number (Binary mode files) at which writing begins.
varname Required. Name of the variable containing data to be written to disk.

Remarks

Data written with Put is usually read from a file with Get.

The first record or byte in a file is at position 1, the second record or byte is at position 2, and so on. If you omit recnumber, the next record or byte after the last Get or Put statement, or pointed to by the last Seek function, is written. You must include delimiting commas, for example:

Put #4,,FileBuffer

For files opened in Random mode, the following rules apply:

  • If the length of the data being written is less than the length specified in the Len clause of the Open statement, Put writes subsequent records on record-length boundaries. The space between the end of one record and the beginning of the next record is padded with the existing contents of the file buffer. Because the amount of padding data can't be determined with any certainty, it is generally a good idea to have the record length match the length of the data being written. If the length of the data being written is greater than the length specified in the Len clause of the Open statement, an error occurs.

  • If the variable being written is a variable-length string, Put writes a 2-byte descriptor containing the string length and then the variable. The record length specified by the Len clause in the Open statement must be at least 2 bytes greater than the actual length of the string.

  • If the variable being written is a Variant of a numeric type, Put writes 2 bytes identifying the VarType of the Variant and then writes the variable. For example, when writing a Variant of VarType 3, Put writes 6 bytes: 2 bytes identifying the Variant as VarType 3 (Long) and 4 bytes containing the Long data. The record length specified by the Len clause in the Open statement must be at least 2 bytes greater than the actual number of bytes required to store the variable.

    Note

    Use the Put statement to write a Variant array to disk, but you can't use Put to write a scalar Variant containing an array to disk. You also can't use Put to write objects to disk.

  • If the variable being written is a Variant of VarType 8 (String), Put writes 2 bytes identifying the VarType, 2 bytes indicating the length of the string, and then writes the string data. The record length specified by the Len clause in the Open statement must be at least 4 bytes greater than the actual length of the string.

  • If the variable being written is a dynamic array, Put writes a descriptor whose length equals 2 plus 8 times the number of dimensions, that is, 2 + 8 * NumberOfDimensions. The record length specified by the Len clause in the Open statement must be greater than or equal to the sum of all the bytes required to write the array data and the array descriptor. For example, the following array declaration requires 118 bytes when the array is written to disk.

    Dim MyArray(1 To 5,1 To 10) As Integer

  • The 118 bytes are distributed as follows: 18 bytes for the descriptor (2 + 8 * 2), and 100 bytes for the data (5 * 10 * 2).

  • If the variable being written is a fixed-size array, Put writes only the data. No descriptor is written to disk.

  • If the variable being written is any other type of variable (not a variable-length string or a Variant), Put writes only the variable data. The record length specified by the Len clause in the Open statement must be greater than or equal to the length of the data being written.

  • Put writes elements of user-defined types as if each were written individually, except that there is no padding between elements. On disk, a dynamic array in a user-defined type written with Put is prefixed by a descriptor whose length equals 2 plus 8 times the number of dimensions, that is, 2 + 8 * NumberOfDimensions. The record length specified by the Len clause in the Open statement must be greater than or equal to the sum of all the bytes required to write the individual elements, including any arrays and their descriptors.

For files opened in Binary mode, all of the Random rules apply, except:

  • The Len clause in the Open statement has no effect. Put writes all variables to disk contiguously; that is, with no padding between records.

  • For any array other than an array in a user-defined type, Put writes only the data. No descriptor is written.

  • Put writes variable-length strings that are not elements of user-defined types without the 2-byte length descriptor. The number of bytes written equals the number of characters in the string. For example, the following statements write 10 bytes to file number 1:

      VarString$ = String$(10," ") 
  Put #1,,VarString$

Example

This example uses the Put statement to write data to a file. Five records of the user-defined type are written to the file.

Type Record ' Define user-defined type. 
 ID As Integer 
 Name As String * 20 
End Type 
 
Dim MyRecord As Record, RecordNumber ' Declare variables. 
' Open file for random access. 
Open "TESTFILE" For Random As #1 Len = Len(MyRecord) 
For RecordNumber = 1 To 5 ' Loop 5 times. 
 MyRecord.ID = RecordNumber ' Define ID. 
 MyRecord.Name = "My Name" & RecordNumber ' Create a string. 
 Put #1, RecordNumber, MyRecord ' Write record to file. 
Next RecordNumber 
Close #1 ' Close file.

See also

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