# Read input stream until the next white space?

**URL:** <https://discourse.julialang.org/t/read-input-stream-until-the-next-white-space/84241>\
**Category:** General Usage\
**Tags:** io\
**Created:** [July 14, 2022, 8:14pm UTC](https://discourse.julialang.org/t/read-input-stream-until-the-next-white-space/84241 "2022-07-14T20:14:30Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![greatpet](https://avatars.discourse-cdn.com/v4/letter/g/e495f1/32.png) [@greatpet](https://discourse.julialang.org/u/greatpet)\
**Post date:** [July 14, 2022, 8:14pm UTC](https://discourse.julialang.org/t/read-input-stream-until-the-next-white-space/84241/1 "2022-07-14T20:14:30Z")

</div>

The function `readuntil` allows you to read an IO buffer until a specified character which could be e.g. the spacebar `' '`. Is there a similar function which allows you to read until any whitespace (space, tab, newline etc.)? I can always read a line and run `split`, but this can be inefficient if the line is extremely long. For example, what’s the easiest way to write code to read a million integers, separated by arbitrary whitespace, one by one, without ever allocating memory to read a long line or otherwise a large chunk of the file?

P.S. This is easy with `scanf()` in C if I’m not mistaken, since it terminates at whitespace by default.

---

<div class="post-metadata">

**Author:** ![greatpet](https://avatars.discourse-cdn.com/v4/letter/g/e495f1/32.png) [@greatpet](https://discourse.julialang.org/u/greatpet)\
**Post date:** [July 14, 2022, 11:31pm UTC](https://discourse.julialang.org/t/read-input-stream-until-the-next-white-space/84241/2 "2022-07-14T23:31:51Z")

</div>

Here’s my own attempt.

```julia
using StaticArrays

function read_int64_until_whitespace(io::IO)::Union{Int64, Nothing}
    v = MVector{20, Char}(undef) # Char vector of length 20 is enough to hold a string of any positive or negative Int64
    len = 0 # actual length used

    c = ' '
    
    while !eof(io) && isspace(c)
        c = read(io, Char)
    end # read until first non-whitespace character
    
    while !isspace(c) # store non-whitespace characters in Char array
        len += 1
        v[len] = c
        if eof(io)
            break
        end
        c = read(io, Char)
    end

    if (len == 0) # if only whitespace is found, return `nothing`
        nothing
    else
        truncated = @view v[1:len]
        parse(Int64, String(truncated))
    end
end

```

Example usage:

```julia
julia> io = IOBuffer("23\n-45 78");

julia> read_int64_until_whitespace(io)
23

julia> read_int64_until_whitespace(io)
-45

julia> read_int64_until_whitespace(io)
78

```

But my code seems too verbose compared with the C version

```
#include <inttypes.h>
scanf("%" SCNd64, &your_variable);

```

or C++ version

```
cin >> your_variable;

```

Any suggestions?

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<div class="post-metadata">

**Author:** ![Jeff\_Emanuel](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jeff_emanuel/32/15440_2.png) [@Jeff\_Emanuel](https://discourse.julialang.org/u/Jeff_Emanuel)\
**Post date:** [July 15, 2022, 2:27pm UTC](https://discourse.julialang.org/t/read-input-stream-until-the-next-white-space/84241/3 "2022-07-15T14:27:46Z")

</div>

> **[GitHub - KlausC/Scanf.jl: The C-style formatted scanf as a companion of...](https://github.com/KlausC/Scanf.jl)**
>
> The C-style formatted scanf as a companion of stdlib/Printf - GitHub - KlausC/Scanf.jl: The C-style formatted scanf as a companion of stdlib/Printf

```julia
julia> using Scanf

julia> b = IOBuffer(" \t\v 3289\n\ncraoeuhrcaohuec")
IOBuffer(data=UInt8[...], readable=true, writable=false, seekable=true, append=false, size=25, maxsize=Inf, ptr=1, mark=-1)

julia> @scanf(b, " %d ", Int)
(1, 3289)

```