Wiki source for KeyPgField


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{{fbdoc item="title" value="FIELD"}}----
Specifies field alignment.

{{fbdoc item="syntax"}}##
[[KeyPgType|Type]]|[[KeyPgUnion|Union]] //typename// **Field** = { 1 | 2 | 4 }
...
End [[KeyPgType|Type]]|[[KeyPgUnion|Union]]
##
{{fbdoc item="desc"}}
##**Field**## can be used to pack ##[[KeyPgType|Types]]## or ##[[KeyPgUnion|Unions]]## more tightly than [[DevStructLayout|the default layout]]. The most commonly used value is ##**Field = 1**##, which causes the ##Type## or ##Union## to be packed as tightly as possible, without any padding bytes being added between the fields or at the end of the ##Type##. ##**Field**## can only be used to decrease field alignment, but it cannot be used to increase it. In order to add padding bytes, a ##Union## with appropriate members could be used instead.

{{fbdoc item="ex"}}
{{fbdoc item="filename" value="examples/manual/udt/field.bas"}}%%(freebasic)
type bitmap_header field = 1
bfType as ushort
bfsize as ulong
bfReserved1 as ushort
bfReserved2 as ushort
bfOffBits as ulong
biSize as ulong
biWidth as ulong
biHeight as ulong
biPlanes as ushort
biBitCount as ushort
biCompression as ulong
biSizeImage as ulong
biXPelsPerMeter as ulong
biYPelsPerMeter as ulong
biClrUsed as ulong
biClrImportant as ulong
end type

dim bmp_header as bitmap_header

'Open up bmp.bmp and get its header data:
'Note: Will not work without a bmp.bmp to load . . .
open "bmp.bmp" for binary as #1

get #1, , bmp_header

close #1

print bmp_header.biWidth, bmp_header.biHeight

sleep

%%

{{fbdoc item="lang"}}
-In the //[[CompilerOptlang|-lang qb]]// dialect, the compiler assumes ##**Field = 1**## by default, if no other ##**Field**## was specified, causing all structures to be tightly packed, without added padding, as in QB.

{{fbdoc item="diff"}}
- In QB ##**Field**## was used to define fields in a file buffer at run time. This feature is not implemented in FB, so the keyword has been redefined. To define fields in a file buffer, ##**[[KeyPgType|Type]]s**## must be used.

{{fbdoc item="see"}}
- ##[[KeyPgType|Type]]##
- ##[[KeyPgUnion|Union]]##
- [[DevStructLayout|Structure packing/field alignment]]

{{fbdoc item="back" value="CatPgUserDefTypes|User Defined Types"}}
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