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author | Tom Tromey <tom@tromey.com> | 2015-11-17 21:18:20 -0700 |
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committer | Tom Tromey <tom@tromey.com> | 2016-02-22 16:07:55 -0700 |
commit | 38a4d72c95936d27cba1ac6e84e3094ffdfaa77c (patch) | |
tree | 389d99afd9cb696fc3ac6b35ee91b8d6d4dce64f /doc/libffi.texi | |
parent | f2f234aef203a5e836b83cb772f9473f7ea0d5ce (diff) | |
download | libffi-38a4d72c95936d27cba1ac6e84e3094ffdfaa77c.tar.gz |
add ffi_get_struct_offsets
Diffstat (limited to 'doc/libffi.texi')
-rw-r--r-- | doc/libffi.texi | 30 |
1 files changed, 27 insertions, 3 deletions
diff --git a/doc/libffi.texi b/doc/libffi.texi index 5c9fddd..94b7a9e 100644 --- a/doc/libffi.texi +++ b/doc/libffi.texi @@ -440,7 +440,8 @@ on the chosen ABI. @item The size and alignment of a new structure type will not be set by -@code{libffi} until it has been passed to @code{ffi_prep_cif}. +@code{libffi} until it has been passed to @code{ffi_prep_cif} or +@code{ffi_get_struct_offsets}. @item A structure type cannot be shared across ABIs. Instead each ABI needs @@ -448,8 +449,9 @@ its own copy of the structure type. @end itemize So, before examining these fields, it is safest to pass the -@code{ffi_type} object to @code{ffi_prep_cif} first. This function -will do all the needed setup. +@code{ffi_type} object to @code{ffi_prep_cif} or +@code{ffi_get_struct_offsets} first. This function will do all the +needed setup. @example ffi_type *desired_type; @@ -463,6 +465,28 @@ if (ffi_prep_cif (&cif, desired_abi, 0, desired_type, NULL) == FFI_OK) @} @end example +@code{libffi} also provides a way to get the offsets of the members of +a structure. + +@findex ffi_get_struct_offsets +@defun ffi_status ffi_get_struct_offsets (ffi_abi abi, ffi_type *struct_type, size_t *offsets) +Compute the offset of each element of the given structure type. +@var{abi} is the ABI to use; this is needed because in some cases the +layout depends on the ABI. + +@var{sizes} is an out parameter. The caller is responsible for +providing enough space for all the results to be written -- one +element per element type in @var{struct_type}. If @var{sizes} is +@code{NULL}, then the type will be laid out but not otherwise +modified. This can be useful for accessing the type's size or layout, +as mentioned above. + +This function returns @code{FFI_OK} on success; @code{FFI_BAD_ABI} if +@var{abi} is invalid; or @code{FFI_BAD_TYPEDEF} if @var{struct_type} +is invalid in some way. Note that only @code{FFI_STRUCT} types are +valid here. +@end defun + @node Arrays Unions Enums @subsection Arrays, Unions, and Enumerations |