method

sysread

v1_9_1_378 - Show latest stable - Class: IO

sysread(p1, p2 = v2)

public

Reads integer bytes from ios using a low-level read and returns them as a string. Do not mix with other methods that read from ios or you may get unpredictable results. If the optional outbuf argument is present, it must reference a String, which will receive the data. Raises SystemCallError on error and EOFError at end of file.

f = File.new("testfile")
f.sysread(16)   #=> "This is line one"

static VALUE
rb_io_sysread(int argc, VALUE *argv, VALUE io)
{
    VALUE len, str;
    rb_io_t *fptr;
    long n, ilen;

    rb_scan_args(argc, argv, "11", &len, &str);
    ilen = NUM2LONG(len);

    if (NIL_P(str)) {
        str = rb_str_new(0, ilen);
    }
    else {
        StringValue(str);
        rb_str_modify(str);
        rb_str_resize(str, ilen);
    }
    if (ilen == 0) return str;

    GetOpenFile(io, fptr);
    rb_io_check_readable(fptr);

    if (READ_DATA_BUFFERED(fptr)) {
        rb_raise(rb_eIOError, "sysread for buffered IO");
    }

    n = fptr->fd;
    rb_thread_wait_fd(fptr->fd);
    rb_io_check_closed(fptr);
    if (RSTRING_LEN(str) != ilen) {
        rb_raise(rb_eRuntimeError, "buffer string modified");
    }

    n = rb_read_internal(fptr->fd, RSTRING_PTR(str), ilen);

    if (n == -1) {
        rb_sys_fail_path(fptr->pathv);
    }
    rb_str_set_len(str, n);
    if (n == 0 && ilen > 0) {
        rb_eof_error();
    }
    rb_str_resize(str, n);
    OBJ_TAINT(str);

    return str;
}

sysread

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