How does scanf(" %[^\n]", str); work in C Programming?

Question

I encountered this in a C program:

char str[100];
scanf(" %[^\n]", str);

Please explain how it works and why?

this means scan everything till you encounter `Enter` means newline character — sinsuren, Oct 14 '16 at 08:32
A good source for answers is the [documentation](http://www.cplusplus.com/reference/cstdio/scanf/), which has explanations of the supported format specifiers — UnholySheep, Oct 14 '16 at 08:33

score 11 · Accepted Answer · answered Oct 14 '16 at 09:32

11

This scanf format string consists of two parts:

a space character, which skips space characters (' ', '\t', '\n', etcetera) in the input, and
the %[^\n] conversion specification, which matches a string of all characters not equal to the new line character ('\n') and stores it (plus a terminating '\0' character) in str.

Note however that if the input (after the leading spaces, and before the first newline character) is longer than 99 characters, this function exhibits undefined behaviour, because str can only hold 100 chars including the terminating '\0' character. A safer alternative is:

scanf(" %99[^\n]", str);

answered Oct 14 '16 at 09:32

well if the size of stris greater than 100 should it work except scanf("%99[^\n]", str); – Joy Ram Sen Gupta Oct 14 '16 at 11:06
It may work, it may not work. Its behaviour is undefined. – Oct 14 '16 at 12:13
Or, if you're using a modern libc, `char *str=NULL; scanf(" %m[^n]", &str);` then remember to `free(str)` later. – nmichaels Nov 01 '17 at 15:39
can't you just do %s? – martiwg Jan 17 '21 at 13:17

score 2 · Answer 2 · answered Oct 14 '16 at 08:33

2

[^\n] searches for line break

hence it will scan for the string until enter is pressed

answered Oct 14 '16 at 08:33

Atal Kishore

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Is it okay to say `searches for line break` – sinsuren Oct 14 '16 at 08:35

How does scanf(" %[^\n]", str); work in C Programming?

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