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instance method
IO#set_encoding_by_bom
set_encoding_by_bom → encoding or nil
io.c
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static VALUE
rb_io_set_encoding_by_bom(VALUE io)
{
rb_io_t *fptr;
GetOpenFile(io, fptr);
if (!(fptr->mode & FMODE_BINMODE)) {
rb_raise(rb_eArgError, "ASCII incompatible encoding needs binmode");
}
if (fptr->encs.enc2) {
rb_raise(rb_eArgError, "encoding conversion is set");
}
else if (fptr->encs.enc && fptr->encs.enc != rb_ascii8bit_encoding()) {
rb_raise(rb_eArgError, "encoding is set to %s already",
rb_enc_name(fptr->encs.enc));
}
if (!io_set_encoding_by_bom(io)) return Qnil;
return rb_enc_from_encoding(fptr->encs.enc);
}
If the stream begins with a BOM (byte order marker), consumes the BOM and sets the external encoding accordingly; returns the result encoding if found, or nil otherwise:
Example
File.write('t.tmp', "\u{FEFF}abc") io = File.open('t.tmp', 'rb') io.set_encoding_by_bom # => #<Encoding:UTF-8> io.close File.write('t.tmp', 'abc') io = File.open('t.tmp', 'rb') io.set_encoding_by_bom # => nil io.close
Raises an exception if the stream is not binmode or its encoding has already been set.