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(Created page with "The EOF function indicates that the end of a file has been reached. {{PageSyntax}} : {{Parameter|endReached%%}} = EOF([#]{{Parameter|fileNumber&}}) {{PageDescription}} * {{Parameter|fileNumber&}} is the number of the file being read. '''#''' is not required. * Returns 0 until the end of a file. This avoids a file read error. * Returns -1 (true) at the end of the file. <!-- confusing statement; further details are required: * CHR$(26) can be used to denote th...") |
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The | The '''EOF''' function indicates that the end of a file or HTTP response has been reached. | ||
{{PageSyntax}} | {{PageSyntax}} | ||
: {{Parameter|endReached%%}} = EOF([#]{{Parameter|fileNumber&}}) | : {{Parameter|endReached%%}} = [[EOF]]([#]{{Parameter|fileNumber&}}) | ||
: {{Parameter|endReached%%}} = [[EOF]]([#]{{Parameter|httpHandle&}}) | |||
{{PageDescription}} | {{PageDescription}} | ||
* {{Parameter|fileNumber&}} is the number of the file being read. '''#''' is not required. | * {{Parameter|fileNumber&}} or {{Parameter|httpHandle&}} is the number of the file or HTTP connected being read. '''#''' is not required. | ||
** {{Parameter|fileNumber&}} is a file opened using [[OPEN]]. | |||
** {{Parameter|httpHandle&}} is a HTTP connection opened using [[_OPENCLIENT]]. | |||
* Returns 0 until the end of a file. This avoids a file read error. | * Returns 0 until the end of a file. This avoids a file read error. | ||
* Returns -1 | * Returns ''true(-1)'' at the end of the file. | ||
* | === Notes === | ||
* In files opened with the [[INPUT (file mode)]] the '''EOF''' function returns '''true''' after any used input function reads a [[CHR$]](26) (Ctrl-Z) from the file, which denotes the "logical" end of a file. This is not necessarily equal to the "physical" end. | |||
** Although this subtle behavior is not required nowadays, it is still here for the sake of compatibility. If you're interested in the historic cause of it see [https://devblogs.microsoft.com/oldnewthing/20040316-00/?p=40233 this Article]. | |||
** To be able to read those files completely use the [[BINARY|BINARY (file mode)]] instead, which is also much faster when used in conjunction with the regular [[INPUT (file statement)|INPUT]], [[LINE INPUT (file statement)|LINE INPUT]] and [[INPUT$]] functions. | |||
* [[GET]] can return invalid data at the end of a file. Read '''EOF''' after a [[GET]] operation to see if the end of the file has been reached and discard the last read if required. | |||
** This is not a problem when using [[GET]] with HTTP connections with a variable length string, the string will always only contain valid data or be empty. | |||
{{PageExamples}} | |||
;Example 1:Showing the difference between INPUT and BINARY file modes when Ctrl-Z is involved. | |||
{{CodeStart}} | |||
'Write a simple test file with Ctrl-Z in the middle. | |||
{{Cl|OPEN}} "test.txt" {{Cl|FOR}} {{Cl|OUTPUT}} {{Cl|AS}} #1 | |||
{{Cl|PRINT}} #1, "Hello"; {{Cl|CHR$}}(26); "World!" | |||
{{Cl|CLOSE}} #1 | |||
'Now read it back, but uhh, this gives us the "Hello" | |||
'only because of the Ctrl-Z. | |||
{{Cl|OPEN}} "test.txt" {{Cl|FOR}} {{Cl|INPUT}} {{Cl|AS}} #1 | |||
{{Cl|WHILE}} {{Cl|NOT}} {{Cl|EOF}}(1) | |||
{{Cl|PRINT}} {{Cl|INPUT$}}(1, 1); | |||
{{Cl|WEND}} | |||
{{Cl|CLOSE}} #1 | |||
{{Cl|PRINT}}: {{Cl|PRINT}} | |||
'However, it works in the BINARY file mode. | |||
{{Cl|OPEN}} "test.txt" {{Cl|FOR}} {{Cl|BINARY}} {{Cl|AS}} #1 | |||
{{Cl|WHILE}} {{Cl|NOT}} {{Cl|EOF}}(1) | |||
{{Cl|PRINT}} {{Cl|INPUT$}}(1, 1); | |||
{{Cl|WEND}} | |||
{{Cl|CLOSE}} #1 | |||
{{CodeEnd}} | |||
{{OutputStart}} | |||
Hello | |||
Hello→World! | |||
{{OutputEnd}} | |||
Latest revision as of 00:34, 18 November 2024
The EOF function indicates that the end of a file or HTTP response has been reached.
Syntax
Description
- fileNumber& or httpHandle& is the number of the file or HTTP connected being read. # is not required.
- fileNumber& is a file opened using OPEN.
- httpHandle& is a HTTP connection opened using _OPENCLIENT.
- Returns 0 until the end of a file. This avoids a file read error.
- Returns true(-1) at the end of the file.
Notes
- In files opened with the INPUT (file mode) the EOF function returns true after any used input function reads a CHR$(26) (Ctrl-Z) from the file, which denotes the "logical" end of a file. This is not necessarily equal to the "physical" end.
- Although this subtle behavior is not required nowadays, it is still here for the sake of compatibility. If you're interested in the historic cause of it see this Article.
- To be able to read those files completely use the BINARY (file mode) instead, which is also much faster when used in conjunction with the regular INPUT, LINE INPUT and INPUT$ functions.
- GET can return invalid data at the end of a file. Read EOF after a GET operation to see if the end of the file has been reached and discard the last read if required.
- This is not a problem when using GET with HTTP connections with a variable length string, the string will always only contain valid data or be empty.
Examples
- Example 1
- Showing the difference between INPUT and BINARY file modes when Ctrl-Z is involved.
'Write a simple test file with Ctrl-Z in the middle. OPEN "test.txt" FOR OUTPUT AS #1 PRINT #1, "Hello"; CHR$(26); "World!" CLOSE #1 'Now read it back, but uhh, this gives us the "Hello" 'only because of the Ctrl-Z. OPEN "test.txt" FOR INPUT AS #1 WHILE NOT EOF(1) PRINT INPUT$(1, 1); WEND CLOSE #1 PRINT: PRINT 'However, it works in the BINARY file mode. OPEN "test.txt" FOR BINARY AS #1 WHILE NOT EOF(1) PRINT INPUT$(1, 1); WEND CLOSE #1 |
Hello Hello→World! |
See also