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[DOC] Refine about offset directives

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Nobuyoshi Nakada 2024-09-29 19:07:16 +09:00
parent 066ac0fdc2
commit e7144af750
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Notes: git 2024-09-29 11:45:37 +00:00 
Merged: https://github.com/ruby/ruby/pull/11721
1 changed files with 23 additions and 7 deletions
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doc/packed_data.rdoc
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@ -564,26 +564,42 @@ for one byte in the input or output string.
== Offset Directives
- <tt>'@'</tt> - Begin packing at the given byte offset;
for packing, null fill if necessary:
for packing, null fill or shrink if necessary:
[1, 2].pack("C@0C") # => "\x02"
[1, 2].pack("C@1C") # => "\x01\x02"
[1, 2].pack("C@5C") # => "\x01\x00\x00\x00\x00\x02"
[1, 2].pack("C@0C") # => "\x02"
[1, 2].pack("C@1C") # => "\x01\x02"
[1, 2].pack("C@5C") # => "\x01\x00\x00\x00\x00\x02"
[*1..5].pack("CCCC@2C") # => "\x01\x02\x05"
For unpacking, cannot to move to outside the string:
"\x01\x00\x00\x02".unpack("C@3C") # => [1, 2]
"\x00".unpack("@1C") # => [nil]
"\x00".unpack("@2C") # Raises ArgumentError.
- <tt>'X'</tt> - Back up a byte:
- <tt>'X'</tt> - For packing, shrink for the given byte offset:
[0, 1, 2].pack("CCXC") # => "\x00\x02"
[0, 1, 2].pack("CCX2C") # => "\x02"
For unpacking; rewind unpacking position for the given byte offset:
"\x00\x02".unpack("CCXC") # => [0, 2, 2]
== Null Byte Directive
Cannot to move to outside the string:
- <tt>'x'</tt> - Null byte:
[0, 1, 2].pack("CCX3C") # Raises ArgumentError.
"\x00\x02".unpack("CX3C") # Raises ArgumentError.
- <tt>'x'</tt> - Begin packing at after the given byte offset;
for packing, null fill if necessary:
[].pack("x0") # => ""
[].pack("x") # => "\x00"
[].pack("x8") # => "\x00\x00\x00\x00\x00\x00\x00\x00"
For unpacking, cannot to move to outside the string:
"\x00\x00\x02".unpack("CxC") # => [0, 2]
"\x00\x00\x02".unpack("x3C") # => [nil]
"\x00\x00\x02".unpack("x4C") # Raises ArgumentError