printf_p Positional Parameters
Positional parameters provide the ability to specify by number which of the arguments is to be substituted into a field in a format string. The following positional parameter printf functions are available:
By default the positional functions behave identically to the non position ones, if no positional formatting is present. Positional parameters are specified using the format "%m$x", where m denotes a numeric ordinal number indicating the position of the parameter in the list of parameters, preceding the format string and x denotes the type field character type specified in the printf function. The parameters in the list are indexed starting at the value 1 for the first element in the list and so forth. For additional information concerning type field characters, see printf Type Field Characters.
For an example of this behavior:
_printf_p("%1$s %2$s", "November", "10");
will print
November 10
The order of the numbers used need not match the order of the arguments given. Thus the following is valid:
_printf_p("%2$s %1$s", "November", "10");
will print
10 November
Parameter may be used more than once while formatting, unlike in traditional format strings, so that
_printf_p("%{1$d times %1$d is %2$d", 10, 100);
will print
10 times 10 is 100
However, all arguments must be used at least once somewhere in the format string.
The maximum number of positional parameters allowed in a format string is given by _ARGMAX.
// positional_args.c
// Positional arguments allow the specification of the order
// in which arguments are consumed in a formatting string.
#include <stdio.h>
int main(int argc, char *argv[])
{
int i = 1,
j = 2,
k = 3;
double x = 0.1,
y = 0.2,
z = 0.3;
char *s1 = "abc",
*s2 = "def",
*s3 = "ghi";
// If positional arguments are unspecified,
// normal input order is used.
_printf_p("%d %d %d\n", i, j, k);
// Positional args are numbers indicating the
// argument enclosed in curly braces.
_printf_p("%3$d %1$d %2$d\n", i, j, k);
// The same positional argument may be reused.
_printf_p("%1$d %2$d %1$d\n", i, j);
_printf_p("%1$s %2$s %3$s\n", s1, s2, s3);
_printf_p("%3$s %1$s %2$s\n", s1, s2, s3);
}
1 2 3 3 1 2 1 2 1 abc def ghi ghi abc def
