c11: use _Generic raise SIGSEGV

Question

here is my code, I try sample code from here

#include <stdio.h>

#define type_idx(T) _Generic( (T), char: 1, int: 2, long: 3, default: 0)

int main(int argc, char *argv[]) {
    puts(type_idx("smth"));
}

the output in clion is:

/home/roroco/.CLion12/system/cmake/generated/c9a7a4c5/c9a7a4c5/Debug/ex/ex
Signal: SIGSEGV (Segmentation fault)

and here is my CMakeLists.txt

cmake_minimum_required(VERSION 3.3)
project(c)

set(CMAKE_C_COMPILER /usr/bin/gcc-4.9)
set(CMAKE_CXX_COMPILER /usr/bin/g++-4.9)
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=c11")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")

Lundin · Accepted Answer · 2015-11-16T11:47:09.863

4

The string literal "smth" decays into a pointer of type char*, which will get translated to the default clause of _Generic. You get the value 0, so your code is equivalent to

puts(0);

Which doesn't make any sense and will cause your program to crash.

edited Nov 16 '15 at 11:47

answered Nov 16 '15 at 10:57

Lundin

195,001
40
254
396

1

Put a `const` in there so I could upvote with a clear conscience. – Bathsheba Nov 16 '15 at 11:00
2

@Bathsheba But the edit made the answer incorrect. `char*` (due to conversion from `char[N]`) is the correct type. – P.P Nov 16 '15 at 11:24
1

I'll put it back, with apologies. – Bathsheba Nov 16 '15 at 11:24
1

Edited the post: to be picky, the literal itself is of type `char [5]` which then decays into a pointer to char. – Lundin Nov 16 '15 at 11:49

c11: use _Generic raise SIGSEGV

1 Answers1