dprintf_bench.c

#include <fcntl.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>

void fdprintf(int fd, const char *fmt, ...)
{
	/* Guess we need no more than 100 bytes. */
	int n, size = 100;
	char *p, *np;
	va_list ap;

	if (fd < 0)
		return;
	if ((p = (char *)malloc(size)) == NULL)
		return;

	while (1)
	{
		/* Try to print in the allocated space. */
		va_start(ap, fmt);
		n = vsnprintf(p, size, fmt, ap);
		va_end(ap);
		/* If that worked, return the string. */
		if (n > -1 && n < size)
		{
			write(fd, p, n);
			free(p);
			return;
		}
		/* Else try again with more space. */
		if (n > -1)    /* glibc 2.1 */
			size = n + 1; /* precisely what is needed */
		else           /* glibc 2.0 */
			size *= 2;  /* twice the old size */
		if ((np = (char *)realloc(p, size)) == NULL)
		{
			free(p);
			return;
		}
		else
		{
			p = np;
		}
	}
}

int new_fdprintf(int fd, const char *fmt, ...)
{
	FILE *file;

	if ((file = fdopen(dup(fd), "w")) == NULL)
	{
		return -1;
	}

	va_list ap;

	va_start(ap, fmt);
	int ret = vfprintf(file, fmt, ap);
	fclose(file);
	va_end(ap);

	return ret;
}

int main(int argc, char *argv[])
{
	int age = atoi(argv[2]);

	int fd = open(argv[3], O_WRONLY | O_CREAT);
	if (fd == -1)
		exit(-1);

	clock_t start_time = clock();
	if (start_time == -1)
		exit(-1);

	for (int i = 0; i < 1000; ++i)
	{
		new_fdprintf(fd, "hi %s how are you?\n did you know your are %d year old?????aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\n", argv[1], age);
	}

	clock_t end_time = clock();
	if (end_time == -1)
		exit(-1);

	printf("new_fdprintf: %d\n", end_time - start_time);

	start_time = clock();
	if (start_time == -1)
		exit(-1);

	for (int i = 0; i < 1000; ++i)
	{
		fdprintf(fd, "hi %s how are you?\n did you know your are %d year old?????aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\n", argv[1], age);
	}

	end_time = clock();
	if (end_time == -1)
		exit(-1);

	printf("old_fdprintf: %d\n", end_time - start_time);

	start_time = clock();
	if (start_time == -1)
		exit(-1);

	for (int i = 0; i < 1000; ++i)
	{
		dprintf(fd, "hi %s how are you?\n did you know your are %d year old?????aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\n", argv[1], age);
	}

	end_time = clock();
	if (end_time == -1)
		exit(-1);

	printf("dprintf: %d\n", end_time - start_time);

	return 0;
}