Is there a built-in way to swap two variables in C

Question

I know how to swap 2 variables in c++ , ie you use std::swap(a,b).

question:

Does the C standard library have a similar function

Answer 1

In C this is often done using a macro,
there are very simplistic examples, eg:
#define SWAP(type,a,b) {type _tmp=a;a=b;b=_tmp;}
... but I wouldn't recommend using them because they have some non-obvious flaws.

This is a macro written to avoid accidental errors.

#define SWAP(type, a_, b_) \
do { \
    struct { type *a; type *b; type t; } SWAP; \
    SWAP.a  = &(a_); \
    SWAP.b  = &(b_); \
    SWAP.t  = *SWAP.a; \
    *SWAP.a = *SWAP.b; \
    *SWAP.b =  SWAP.t; \
} while (0)

• Each argument is instantiated only once,
  so SWAP(a[i++], b[j++]) doesn't give problem side effects.
• temp variable name is also SWAP, so as not to cause bugs if a different name happens to collide with the hard-coded name chosen.
• It doesn't call memcpy (which in fact ended up doing real function calls in my tests, even though a compiler may optimize them out).
• Its type-checked
  (comparing as pointers makes the compiler warn if they don't match).