Virtual function check (C vs C++)

compilation_and_output

isis:cpp_vs_c alex$ gcc -O3 -std=c99 virt.c -o /tmp/v
isis:cpp_vs_c alex$ gcc -O3  virt.cpp -o /tmp/vpp
isis:cpp_vs_c alex$ /tmp/v

Ret = 100001000, Time: 0 sec 188086 000 msec

isis:cpp_vs_c alex$ /tmp/vpp 

(C++) Ret = 100001000, Time: 0 sec 000001 000 msec

isis:cpp_vs_c alex$ gcc --version
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 5.0 (clang-500.2.79) (based on LLVM 3.3svn)
Target: x86_64-apple-darwin13.0.0
Thread model: posix

virt.c

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

#include <sys/time.h>
#define NANO_UNIT       (1000000000LL)

static void printFormattedNanoTime(long long nanoTime, FILE * os) {
    long long sec = nanoTime / NANO_UNIT;
    long long nanos = (nanoTime - (sec * NANO_UNIT));
    fprintf(os, "%lld sec %06lld %03lld msec", sec, nanos / 1000, nanos % 1000);
}

/*
* class Bar {
* public:
*   int member;
*   Bar(int member) { this.member = member; }
*   virtual int add(int a, int b) { return this.member + a + b; }
* }
*/


struct BarVtbl {
  int (* add)(void * this, int a, int b);
};

struct Bar {
  struct BarVtbl * vtbl;
  int member;
};

static int Bar_add(void * this, int a, int b) {
  struct Bar * self = (struct Bar *) this;
  return self->member + a + b;
}

static struct BarVtbl g_BarVtbl = {
  &Bar_add
};

static struct Bar *
Bar_new(int member) {
  struct Bar * b = malloc(sizeof(struct Bar));
  b->vtbl = &g_BarVtbl;
  b->member = member;
  return b;
}

int main(int argc, char * argv[]) {
  struct Bar * b = Bar_new(1000);
  struct timeval start;
  struct timeval stop;
  int ret;

  gettimeofday(&start, NULL);
  for (int i = 0; i < 100000000; ++i) {
    ret = b->vtbl->add(b, i, 1);
  }
  gettimeofday(&stop, NULL);

  long long nanoTime = (stop.tv_sec - start.tv_sec) * NANO_UNIT + (stop.tv_usec - start.tv_usec) * 1000L;
  printf("\nRet = %d, Time: ", ret);
  printFormattedNanoTime(nanoTime, stdout);
  printf("\n\n");

  return 0;
}

virt.cpp

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

#include <sys/time.h>
#define NANO_UNIT       (1000000000LL)

static void printFormattedNanoTime(long long nanoTime, FILE * os) {
    long long sec = nanoTime / NANO_UNIT;
    long long nanos = (nanoTime - (sec * NANO_UNIT));
    fprintf(os, "%lld sec %06lld %03lld msec", sec, nanos / 1000, nanos % 1000);
}


class Bar {
private:
  int member;
public:
  Bar(int member) { this->member = member; }
  virtual int add(int a, int b) {
    return member + a + b;
  }
};

int main(int argc, char * argv[]) {
  Bar b(1000);
  struct timeval start;
  struct timeval stop;
  int ret;

  gettimeofday(&start, NULL);
  for (int i = 0; i < 100000000; ++i) {
    ret = b.add(i, 1); 
  }
  gettimeofday(&stop, NULL);

  long long nanoTime = (stop.tv_sec - start.tv_sec) * NANO_UNIT + (stop.tv_usec - start.tv_usec) * 1000L;
  printf("\n(C++) Ret = %d, Time: ", ret);
  printFormattedNanoTime(nanoTime, stdout);
  printf("\n\n");
  
  return 0;
}