Go-like defer statement for C++

defer.cpp

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>

namespace {

template<typename F>
class ScopeGuard {
 public:
  ScopeGuard(F f) : f_(f) {
  }

  ~ScopeGuard() {
    f_();
  }

 private:
  F f_;
};

#define CAT_(a, b)  a ## b
#define CAT(a, b)  CAT_(a, b)
#define defer_(f, g, e)  auto f = [&]() { e; }; ScopeGuard<decltype(f)> g(f)
#define defer(expr)  defer_(CAT(f, __LINE__), CAT(guard, __LINE__), expr)

}  // namespace


int main() {
  FILE* f = fopen("defer.cpp", "r");
  if (!f) {
    perror("fopen");
    exit(-1);
  }
  defer(fclose(f));

  defer(printf("Yep.\n"));
  defer(printf("Are we there yet?\n"));

  char buf[256];
  ssize_t nread;
  while ((nread = fread(buf, 1, sizeof(buf)-1, f)) > 0) {
    buf[nread] = '\0';
    printf("%s", buf);
  }

  return 0;
}

Bad syntax with the parentheses. ScopeGuard vestiges visible. Making f_ private is unnecessary - shouldn't be touching the variable anyway. Unnecessary double-statement semantics.