Need help about function scanf in C

Question

I'm reading book "C Programming A Modern Approach" and I see a question: Show how can be distinguished: "%f" vs "%f "(after %f have a space) in function scanf().

Can you help me understanding how does "%f " work.

There is some useful scanf related information here: stackoverflow.com/questions/1247989/… — iammowgli
– iammowgli, Commented May 22, 2015 at 3:28
You can see more detail about scanf() function in here. Read description of format, answer of your question is explained so clearly. — Hoang Pham
– Hoang Pham, Commented May 22, 2015 at 6:36

chux · Accepted Answer · 2015-05-22 03:02:43Z

3

"%f" instructs scanf() to

Scan from stdin and discard white-space until no more input or a non-white-space encountered. Put that char back into stdin.
Scan char that represents a float. Continue until no more input or a non-float char encountered. Put that char back into stdin.

"%f " instructs scanf() to the steps 1 and 2 above and then

Scan from stdin and discard white-space until no more input or a non-white-space encountered. Put that char back into stdin. (just like step 1)

Note: All scanf() format specifiers except "%c", "%n", "%[]" perform step 1 before scanning further.

answered May 22, 2015 at 3:02

chux

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Razib · Accepted Answer · 2015-05-22 03:02:00Z

0

The second one required a space followed by a float you entered. If you have multiple float to take from user then you can write something like -

scanf("%f %f", &f1, &f2);

answered May 22, 2015 at 3:02

Razib

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3 Comments

iammowgli Over a year ago

@Nguyen. I believe the only 'spaces' that scanf ignores are: tab, space bar & newline ('enter' key) present in the input stream. When the 'space' is in between format specifiers e.g. scanf("%f %f", ...), it is ignored. But in your second example, there is no other format specifier after the space i.e. ("%f ") ... so it probably expects more data in the stream. Then, after you enter 'something', it attempts to store it in a variable, but since there is only 1 variable 'x' e.g. scanf("%f ", &x), it ignores the 'something' you entered ... and returns.

KajolK Over a year ago

@Nguyễn Văn-Dũng, why are using slang here. You may down vote if you think some post (answer/question) is incorrect of of low quality. Please don't use slang.

chux Over a year ago

@iammowgli In the default "C" locale, white-spaces are space ' ', form feed '\f', new-line '\n', carriage return '\r', horizontal tab '\t', and vertical tab '\v'.

Arun A S · Accepted Answer · 2015-05-22 06:01:07Z

0

if you use the white-space after %f, that is

scanf("%f ");

the scanf() will skip the line-feed character.

edited May 22, 2015 at 6:01

Arun A S

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answered May 22, 2015 at 4:42

Hong Seok

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1 Comment

chux Over a year ago

Note: It will skip a following line-feed character as well an any number of following white-space.

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