| read | file statement |
Dangerous parts
| Syntax | A readStatement is:
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| Description | The read statement inputs each of the readItems from the specified file. These items are input directly using the binary format that they have on the file. In other words, the items are not in source (ASCII or EBCDIC) format. In the common case, these items have been output to the file using the write statement. By contrast, the get and put statements use source format, which a person can read using an ordinary text editor.
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| Example | This example shows how to input a complete employee record using a read statement.
var employeeRecord :
record
name : string ( 30 )
pay : int
dept : 0 .. 9
end record
var fileNo : int
open : fileNo, "payroll", read
…
read : fileNo, employeeRecord
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| Details | The fileNumber must specify a file that is open with read capability (or a program argument file that is implicitly opened). The optional status is an int variable that is set to implementation-dependent information about the read. If status is returned as zero, the read was successful. Otherwise status gives information about the incomplete or failed read (which is not documented here). You commonly use status when you are reading a record or array from a file and you are not sure if the entire item exists on the file. If it does not exist, the read will fail part way through, but your program can continue and diagnose the problem by inspecting status. A readItem is:
variableReference [ : requestedSize [ : actualSize ] ]Each readItem specifies a variable to be read in internal form. The optional requestedSize is an integer value giving the number of bytes of data to be read. The requestedSize should be less than or equal to the size of the item's internal form in memory (else a warning message is issued). If no requestedSize is given, the size of the item in memory is used. The optional actualSize is an int variable that is set to the number of bytes actually read. An array, record or union may be read and written as a whole. It is dangerous to read into pointer variables, as this allows the possibility of creating incorrect addresses in the pointers. It is also dangerous to read more bytes than are in the readItem.
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| See also | the write, open, close, seek, tell, get and put statements.
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