printf: empty precision is interpreted as precision 6, not as precision 0

[bhaible]

Description

The following code:

<?php
  printf("%.f\n", 3.1415926535);
  printf("%.0f\n", 3.1415926535);
  printf("%.6f\n", 3.1415926535);
?>

Resulted in this output:

3.141593
3
3.141593

But I expected this output instead:

3
3
3.141593

because the documentation (https://www.php.net/manual/en/function.printf.php and https://www.php.net/manual/en/function.sprintf.php) says "Note: If the period is specified without an explicit value for precision, 0 is assumed."

PHP Version

PHP 8.3.6 (cli) (built: Mar 19 2025 10:08:38) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.3.6, Copyright (c) Zend Technologies
    with Zend OPcache v8.3.6, Copyright (c), by Zend Technologies

Operating System

No response

[nielsdos]

I believe you're right: not specifying a precision should make it zero as that's how printf works in C where this function originates from. So this is one of the cases where the docs are right but the implementation is wrong.

[nielsdos]

This would do, but I wonder how much of a BC break this is. Perhaps this is master-only material

diff --git a/ext/standard/formatted_print.c b/ext/standard/formatted_print.c
index 9471ad3c7ba..b81fff4e833 100644
--- a/ext/standard/formatted_print.c
+++ b/ext/standard/formatted_print.c
@@ -587,6 +587,7 @@ php_formatted_print(char *format, size_t format_len, zval *args, int argc, int n
 						expprec = 1;
 					} else {
 						precision = 0;
+						adjusting |= ADJ_PRECISION;
 					}
 				} else {
 					precision = 0;

[bhaible]

that's how printf works in C

Yes, that's how printf works in C, Python, Emacs Lisp, librep, Go, Ruby, awk, lua, Free Pascal, D, boost, Tcl, and perl.

This would do

Yes, I believe this patch will fix it.