[samfisher83]

Can you provide C code that will not compile with c++ compiler?

[stephencanon]

Besides the various "bad old programming idioms" that do not compile under C++, there are a few genuinely useful features that have only just been added to C++ more than 15 years after they appeared in C, like hexadecimal floating-point literals (in practice, many compilers supported these, but they were not formally part of the language). Designated struct initializers are another C feature that I would love to have in C++.

[hawski]

Compound literals are outside of C++ standard. However GCC for example supports them, but a bit differently [0].

  $ cat foobar.c
  #include <stdio.h>
  
  struct foo {
  	int x;
  	int y;
  };
  
  int foobar(struct foo *f)
  {
  	return f->x + f->y;
  }
  
  int
  main(int argc, char *argv[]) {
  	(void)argc; (void)argv;
  
  	printf("%d\n", foobar(&(struct foo){10, 20}));
  	return 0;
  }
  $ gcc -Wall -Wcast-align -Wextra -pedantic -std=c99 foobar.c -o foobar && ./foobar
  30
  $ g++ -Wall -Wcast-align -Wextra -pedantic foobar.c -o foobar && ./foobar
  foobar.c: In function ‘int main(int, char**)’:
  foobar.c:17: warning: ISO C++ forbids compound-literals
  foobar.c:17: warning: taking address of temporary
  30
  $ # taking address of temporary means that it's undefined behavior

[0] https://gcc.gnu.org/onlinedocs/gcc/Compound-Literals.html

[astrodust]

Here's a bunch of examples: http://www.geeksforgeeks.org/write-c-program-wont-compiler-c...

[Chromozon]

This is a great example of how many of the things in C that don't compile in C++ are horrible programming practices, and it's really nice that C++ doesn't allow such garbage.

[magnusjonsson]

Actually those are very bad examples. In practice, compilers will produce warnings in all of those examples.

Better examples (of actually useful things) would be things like designated initializers, struct literals, declaring array lengths in args using static, etc.

[milesrout]

I don't see what is 'horrible programming practice' about

    int *x = malloc(sizeof(int));

[maccard]

because malloc doesn't return an int, it returns a void

[milesrout]

malloc returns a void pointer because it implicitly converts to an int pointer, as it should.

[msoucy]

Sure:

struct Foo { int virtual; };

[metaobject]

You're being pedantic about reserved words?

[spc476]

I had that same problem. I wrote a C library [1] that has a structure field named "class". It's "class" because the protocol being described (DNS) calls that particular field "class" [2]. And I'm not about to pay lip service to an abomination like C++ [3][4].

[1] https://github.com/spc476/SPCDNS

[2] https://github.com/spc476/SPCDNS/blob/ca5052c3d0c3252071a18e...

[3] I am NOT a fan of C++.

[4] But I had to anyway, but I used the C pre-processor to rename the field.

[camgunz]

Yeah I super hate this. There's no other language that requires other languages to contort themselves like C++ does. Every time I see `#ifdef __cplusplus` or `klass` my blood pressure spikes.

[sampo]

> Can you provide C code that will not compile with c++ compiler?

C99 native complex numbers

[Ace17]

int* p = malloc(256);