isspace() only works for digits up to 8?

Question

In my code :

cout << "Isspace 5 and 10 are " << isspace(5) << " and " << isspace(10) << endl;

gives 0 and 8. Why does isspace(10) not give 0 since 10 is not a white space?

Note that the space character has value 32, so isspace cannot only work for numbers up to 8 — smac89, Oct 18 '15 at 06:00

score 2 · Answer 1 · answered Oct 18 '15 at 05:54

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Because according to issspace(), 10 (0xa) is a whitespace character (newline/linefeed). See http://www.cplusplus.com/reference/cctype/isspace/

answered Oct 18 '15 at 05:54

Dronz

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John Kugelman · Accepted Answer · 2015-10-18T18:41:36.187

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You're supposed to pass characters to isspace, not integers.

isspace('5') == zero (false)
isspace(' ') == non-zero (true)

When you pass 5 and 10 you're asking it if the characters with ASCII values 5 (ENQ, some rarely used control code) and 10 (LF, line feed, AKA '\n') are whitespace. ENQ is not whitespace, so isspace returns zero. A line feed is whitespace, so isspace returns a non-zero value.

edited Oct 18 '15 at 18:41

answered Oct 18 '15 at 05:53

John Kugelman

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Should "ENQ, line feed" just be "line feed"? – user253751 Oct 18 '15 at 06:06
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Might be useful to note that [documentation](http://en.cppreference.com/w/cpp/string/byte/isspace) that specifies `int ch` usually means a character (hence the `ch`). – Qix - MONICA WAS MISTREATED Oct 18 '15 at 06:18
Seems to me isspace takes integers, to be interpreted as character codes. If someone said "pass foo() a character" I would expect type char. – Dronz Oct 19 '15 at 17:48

score 1 · Answer 3 · answered Oct 18 '15 at 05:56

1

The numbers you are passing are being treated as ASCII characters' numerical representation. 10 is a newline character which is considered by the system to be a white space character.

answered Oct 18 '15 at 05:56

Laserbeak

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isspace() only works for digits up to 8?

3 Answers3