method

read

v1_9_1_378 - Show latest stable - Class: IO

read(p1 = v1, p2 = v2)

public

Reads at most length bytes from the I/O stream, or to the end of file if length is omitted or is nil. length must be a non-negative integer or nil. If the optional buffer argument is present, it must reference a String, which will receive the data.

At end of file, it returns nil or “” depend on length. ios.read() and ios.read(nil) returns “”. ios.read(positive-integer) returns nil.

ios.read(0) returns “”.

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

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

    rb_scan_args(argc, argv, "02", &length, &str);

    if (NIL_P(length)) {
        if (!NIL_P(str)) StringValue(str);
        GetOpenFile(io, fptr);
        rb_io_check_readable(fptr);
        return read_all(fptr, remain_size(fptr), str);
    }
    len = NUM2LONG(length);
    if (len < 0) {
        rb_raise(rb_eArgError, "negative length %ld given", len);
    }

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

    GetOpenFile(io, fptr);
    rb_io_check_readable(fptr);
    if (len == 0) return str;

    READ_CHECK(fptr);
    if (RSTRING_LEN(str) != len) {
        rb_raise(rb_eRuntimeError, "buffer string modified");
    }
    n = io_fread(str, 0, fptr);
    if (n == 0) {
        if (fptr->fd < 0) return Qnil;
        rb_str_resize(str, 0);
        return Qnil;
    }
    rb_str_resize(str, n);
    OBJ_TAINT(str);

    return str;
}

read

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