具有多个单词的字符串的 scanf() 行为

Question

Well I've been programming in C for quite a while now, and there is this question about the function scanf()

here is my problem:

I know that every element in ASCII table is a character and I even know that %s is a data specified for a string which is a collection of characters

My questions:

1.why does scanf() stops scanning after we press enter. If enter is also character why cant it be added as a component of the string that is being scanned.

2.My second question and what I require the most is why does it stops scanning after a space, when space is again a character?

Note: My question is not about how to avoid these but how does this happen

I'd be happy if this is already addressed, I'd gladly delete my question and even if I've presumed something wrong please let me know

Answer 1

"why does scanf() stops scanning after we press enter." is not always true.

The "%s" directs scanf() as follows

char buffer[100];
scanf("%s", buffer);

1. Scan and consume all white-space including '\\n' generated from multiple Enter s. This data is not saved.

Input white-space characters (as specified by the isspace function) are skipped, unless the specification includes a [ , c , or n specifier C11dr §7.21.6.2 8

2. Scan and save all non-white-space characters. Continue doing so until a white-space is encountered.

Matches a sequence of non-white-space characters §7.21.6.2 12

3. This white-space is put back into stdin for the next input function. (OP's 2nd question)
4. A null character is appended to buffer .
5. Operations may stop short if EOF occurs.
6. If too much data is save in buffer , it is UB.
7. If some non-white-space data is saved, return 1. If EOF encountered, return EOF.

Note: stdin is usually line buffered, so no keyboard data is given to stdin until a '\\n' occurs.

Answer 2

From my reading of your question, both of your numbered questions are the same:

Why does scanf with a format specifier of %s stop reading after encountering a space or newline.

And the answer to both of your questions is: Because that is what scanf with the %s format specifier is documented to do.

From the documentation :

%s Matches a sequence of bytes that are not white-space characters.

A space and a newline character (generated by the enter key) are white-space characters.

Answer 3

I made miniprogram with scanf for get multiple name without stop on space or ever enter. i use while

Scanf("%s",text);

While (1)
{
Scanf("%s",text1)
If (text1=='.'){break;}
//here i simple add text1 to text
}

This way i get one line if use the . Now i use scanf("%[^\\n]",text); It work great.