Why both clang and gcc only give a warning when there is a space after backslash if C standard says that whitespace is forbidden?

Question

When compiling the following snippet, both gcc and clang only issue a warning. Notice space after \\ next to int:

#include 

        

Answer 1

Compile with the right options and gcc and clang will refuse to do the translation:

$ gcc -Wall -Werror -std=c11 -pedantic tst.c
tst.c: In function ‘main’:
tst.c:6:9: error: backslash and newline separated by space [-Werror]
cc1: all warnings being treated as errors
$

By default gcc compiles in c89 mode with GNU extensions enabled and is pretty indulgent.