Add support for * width and precision in printf()

If * is used for width/precision in printf, then the width/precision
is provided by a printf argument instead of being part of the format
string. Semantics generally match those of printf in C.

This can be used to easily reproduce PHP's float printing behavior:

    // Locale-sensitive using precision ini setting.
    // Used prior to PHP 8.0.
    sprintf("%.*G", (int) ini_get('precision'), $float);

    // Locale-insensitive using precision ini setting.
    // Used since to PHP 8.0.
    sprintf("%.*H", (int) ini_get('precision'), $float);

    // Locale-insensitive using serialize_precision ini setting.
    // Used in serialize(), json_encode() etc.
    sprintf("%.*H", (int) ini_get('serialize_precision'), $float);

Closes GH-5432.

1 files changed, 7 insertions, 0 deletions

diff --git a/UPGRADING b/UPGRADING
index 6f3abbfc7c..81b945d204 100644
--- a/UPGRADING
+++ b/UPGRADING
@@ -539,6 +539,13 @@ PHP 8.0 UPGRADE NOTES
   . printf() and friends how support the %h and %H format specifiers. These
     are the same as %g and %G, but always use "." as the decimal separator,
     rather than determining it through the LC_NUMERIC locale.
+  . printf() and friends now support using "*" as width or precision, in which
+    case the width/precision is passed as an argument to printf. This also
+    allows using precision -1 with %g, %G, %h and %H. For example, the following
+    code can be used to reproduce PHP's default floating point formatting:
+
+        printf("%.*H", (int) ini_get("precision"), $float);
+        printf("%.*H", (int) ini_get("serialize_precision"), $float);
 
 - Zip:
   . Extension updated to version 1.19.0