To print Pi to five decimal places:
#include <math.h>
#include <stdio.h>
fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0));
To print a date and time in the form "Sunday, July 3, 10:02",
where weekday and month are pointers to strings:
#include <stdio.h>
fprintf(stdout, "%s, %s %d, %.2d:%.2d\n",
weekday, month, day, hour, min);
Many countries use the day-month-year order. Hence, an
internationalized version must be able to print the arguments in
an order specified by the format:
#include <stdio.h>
fprintf(stdout, format,
weekday, month, day, hour, min);
where format depends on locale, and may permute the arguments.
With the value:
"%1$s, %3$d. %2$s, %4$d:%5$.2d\n"
one might obtain "Sonntag, 3. Juli, 10:02".
To allocate a sufficiently large string and print into it (code
correct for both glibc 2.0 and glibc 2.1):
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
char *
make_message(const char *fmt, ...)
{
int n = 0;
size_t size = 0;
char *p = NULL;
va_list ap;
/* Determine required size. */
va_start(ap, fmt);
n = vsnprintf(p, size, fmt, ap);
va_end(ap);
if (n < 0)
return NULL;
size = (size_t) n + 1; /* One extra byte for '\0' */
p = malloc(size);
if (p == NULL)
return NULL;
va_start(ap, fmt);
n = vsnprintf(p, size, fmt, ap);
va_end(ap);
if (n < 0) {
free(p);
return NULL;
}
return p;
}
If truncation occurs in glibc versions prior to 2.0.6, this is
treated as an error instead of being handled gracefully.
