CODEWITHSUNDEEP
c
Krish
Krish

Reputation: 575

\\\ prints just one backslash?

In C, on mentioning three backslashes, like so:

#include <stdio.h>

int main() { 
    printf(" \\\ ");
}

prints out just one backslash in the output. Why and how does this work?

Upvotes: 1

Views: 1475

Answers (4)

Abhijit Pritam Dutta
Abhijit Pritam Dutta

Reputation: 5591

It is indeed a very simple operation in c. A \ is just a escape sequences. Hence below statement will print two slash.

  printf(" \\\\ ");

For example some characters in c are represented with a slash like end of a line character \n or end of a string character \0 etc. But if you want to print such a character as it is what will you do? Hence you need to add a escape sequence character in front of it:

printf("\\n"); // will print \n

But

printf("\n"); // will print end of character hence you don't see anything in output

Upvotes: 1

msc
msc

Reputation: 34638

C11; 6.4.4.4 Character constants:

The double-quote " and question-mark ? are representable either by themselves or by the escape sequences \" and \?, respectively, but the single-quote ' and the backslash \ shall be represented, respectively, by the escape sequences \' and \\.

So, To represent a single backslash, it’s necessary to place double backslashes \\ in the source code. To print two \\ you need four backslash \\\\. In your code extra \ is a space character, which isn't valid.

Upvotes: 1

unwind
unwind

Reputation: 399959

That sequence is:

  • A space
  • A double backslash, which encodes a single backslash in the runtime string
  • A backslash followed by a space, which is not a standard escape sequence and should give you a diagnostic

The C11 draft says (in note 77):

The semantics of these characters were discussed in 5.2.2. If any other character follows a backslash, the result is not a token and a diagnostic is required.

On godbolt.org I got:

<source>:8:14: warning: unknown escape sequence '\ ' [-Wunknown-escape-sequence]

So you seem to be using a non-conforming compiler, which chooses to implement undefined backslash sequences by just letting the character through.

Upvotes: 5

Neil
Neil

Reputation: 11889

That is printing:

space
slash
escaped space

The 3rd slash is being interpreted as "slash space"

Upvotes: 1

Related Questions