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Native File Read R←⎕NREAD Y

This monadic function reads data from a native file. Y is a 3- or 4-element integer vector whose elements are as follows:

[1] negative tie number,
[2] conversion code (see below),
[3] count. If this value is ¯1, all of the elements defined by Y[2] are read from the position specified by Y[4] to the end of the file. This may result in the last few bytes in the file being ignored if they do not form a complete element.
[4] start byte, counting from 0. If this value omitted or is ¯1, data is read starting from the current position in the file (initially 0).

Notes:

8 ⎕NINFO ⊃Y can be used to report the current position of the file pointer.

Y[2] specifies conversion to an APL internal form as follows. Note that the internal formats for character arrays differ between the Unicode and Classic Editions.

If both Y[3] and Y[4] have the value ¯1, then ⎕NREAD reads data from the current position in the file to the end of the file.

⎕NREAD can be used with any file. However, calling ⎕NREAD with at least one of Y[3 4] set to ¯1 is intended for regular files only; using on pipes, FIFOs or other special types of file is not recommended.

Table 48: Unicode Edition: Conversion Codes

Value Number of bytes read Result Type Result shape
11 count 1 bit Boolean 8 × count
80 count 8 bits character count
821 count 8 bits character count
83 count 8 bits integer count
160 2 × count 16-bits character count
163 2 × count 16 bits integer count
320 4 × count 32-bits character count
323 4 × count 32 bits integer count
645 8 × count 64 bits floating count

Table 49: Classic Edition: Conversion Codes

Value Number of bytes read Result Type Result shape
11 count 1 bit Boolean 8 × count
82 count 8 bits character count
83 count 8 bits integer count
163 2 × count 16 bits integer count
323 4 × count 32 bits integer count
645 8 × count 64 bits floating count

Note that types 80, 160 and 320 and 83 and 163 are exclusive to Dyalog APL.

Example

      DATA←⎕NREAD ¯1 160 (0.5×⎕NSIZE ¯1) 0 ⍝ Unicode
      DATA←⎕NREAD ¯1 82 (⎕NSIZE ¯1) 0      ⍝ Classic
      DATA←⎕NREAD ¯1 82 ¯1 0       ⍝ Shorter version