Truncate a file: Difference between revisions
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The task is to demonstrate how to truncate a file to a specific length. This should be implemented as a routine that takes two parameters: the filename and the required file length (in bytes). Truncation can be achieved using system or library calls intended for such a task, if such methods exist, or by creating a temporary file of a reduced size and renaming it, after first deleting the original file, if no other method is available. The file may contain non human readable binary data in an unspecified format, so the routine should be "binary safe", leaving the contents of the untruncated part of the file unchanged. If the specified filename does not exist, or the provided length is not less than the current file length, then the routine should raise an appropriate error condition and exit. On some systems, the provided file truncation facilities might not change the file or may extend the file, if the specified length is greater than the current length of the file. For the purpose of this task, it is permissible for such facilities to be used. Such behaviour should be noted, or optionally a warning message relating to an non change or increase in file size may be implemented. |
The task is to demonstrate how to truncate a file to a specific length. This should be implemented as a routine that takes two parameters: the filename and the required file length (in bytes). Truncation can be achieved using system or library calls intended for such a task, if such methods exist, or by creating a temporary file of a reduced size and renaming it, after first deleting the original file, if no other method is available. The file may contain non human readable binary data in an unspecified format, so the routine should be "binary safe", leaving the contents of the untruncated part of the file unchanged. If the specified filename does not exist, or the provided length is not less than the current file length, then the routine should raise an appropriate error condition and exit. On some systems, the provided file truncation facilities might not change the file or may extend the file, if the specified length is greater than the current length of the file. For the purpose of this task, it is permissible for such facilities to be used. Such behaviour should be noted, or optionally a warning message relating to an non change or increase in file size may be implemented. |
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==Icon and {{header|Unicon}}== |
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Unicon provides the built-in function truncate which can be used to truncate a file. The following line of code truncates ''filename'' to ''newsizeinbytes''. The file is opened for both read and write in untranslated mode. |
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<lang Unicon>truncate(f := open(filename, "bu"), newsizeinbytes) & close(f)</lang> |
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Note: The Unicon book incorrectly indicates that truncate doesn't work on Windows. |
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=={{header|Java}}== |
=={{header|Java}}== |
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