End of Life Ruby 3.0 has reached end of life and gets no more fixes. Switch to Ruby 4.0 →
instance method
IO#ungetc
ios.ungetc(string) → nil
io.c
View on GitHub ↗
VALUE
rb_io_ungetc(VALUE io, VALUE c)
{
rb_io_t *fptr;
long len;
GetOpenFile(io, fptr);
rb_io_check_char_readable(fptr);
if (FIXNUM_P(c)) {
c = rb_enc_uint_chr(FIX2UINT(c), io_read_encoding(fptr));
}
else if (RB_TYPE_P(c, T_BIGNUM)) {
c = rb_enc_uint_chr(NUM2UINT(c), io_read_encoding(fptr));
}
else {
SafeStringValue(c);
}
if (NEED_READCONV(fptr)) {
SET_BINARY_MODE(fptr);
len = RSTRING_LEN(c);
#if SIZEOF_LONG > SIZEOF_INT
if (len > INT_MAX)
rb_raise(rb_eIOError, "ungetc failed");
#endif
make_readconv(fptr, (int)len);
if (fptr->cbuf.capa - fptr->cbuf.len < len)
rb_raise(rb_eIOError, "ungetc failed");
if (fptr->cbuf.off < len) {
MEMMOVE(fptr->cbuf.ptr+fptr->cbuf.capa-fptr->cbuf.len,
fptr->cbuf.ptr+fptr->cbuf.off,
char, fptr->cbuf.len);
fptr->cbuf.off = fptr->cbuf.capa-fptr->cbuf.len;
}
fptr->cbuf.off -= (int)len;
fptr->cbuf.len += (int)len;
MEMMOVE(fptr->cbuf.ptr+fptr->cbuf.off, RSTRING_PTR(c), char, len);
}
else {
NEED_NEWLINE_DECORATOR_ON_READ_CHECK(fptr);
io_ungetbyte(c, fptr);
}
return Qnil;
}
Pushes back one character (passed as a parameter) onto ios, such that a subsequent buffered character read will return it. Only one character may be pushed back before a subsequent read operation (that is, you will be able to read only the last of several characters that have been pushed back). Has no effect with unbuffered reads (such as IO#sysread).
Example
f = File.new("testfile") #=> #<File:testfile> c = f.getc #=> "8" f.ungetc(c) #=> nil f.getc #=> "8"