diff --git a/engine/Math.cpp b/engine/Math.cpp
index f0a0467c..53f4a141 100644
--- a/engine/Math.cpp
+++ b/engine/Math.cpp
@@ -18,6 +18,7 @@
  */
 
 #include "yatemath.h"
+#include <stdio.h>
 
 using namespace TelEngine;
 
@@ -312,17 +313,33 @@ String& BitVector::appendTo(String& buf, unsigned int offs, int len) const
 // Math
 //
 // Append a Complex number to a String (using "%g%+gi" format)
-String& Math::dumpComplex(String& dest, const Complex& val, const char* sep)
+String& Math::dumpComplex(String& dest, const Complex& val, const char* sep,
+    const char* fmt)
 {
-    String tmp;
-    return dest.append(tmp.printf("%g%+gi",val.re(),val.im()),sep);
+    if (TelEngine::null(fmt))
+	fmt = "%g%+gi";
+    else if (::strlen(fmt) > 30) {
+	String tmp;
+	return dest.append(tmp.printf(512,fmt,val.re(),val.im()),sep);
+    }
+    char s[60];
+    ::sprintf(s,fmt,val.re(),val.im());
+    return dest.append(s,sep);
 }
 
 // Append float value to a String (using %g format)
-String& Math::dumpFloat(String& dest, const float& val, const char* sep)
+String& Math::dumpFloat(String& dest, const float& val, const char* sep,
+    const char* fmt)
 {
-    String tmp;
-    return dest.append(tmp.printf("%g",val),sep);
+    if (TelEngine::null(fmt))
+	fmt = "%g";
+    else if (::strlen(fmt) > 30) {
+	String tmp;
+	return dest.append(tmp.printf(512,fmt,val),sep);
+    }
+    char s[60];
+    ::sprintf(s,fmt,val);
+    return dest.append(s,sep);
 }
 
 /* vi: set ts=8 sw=4 sts=4 noet: */
diff --git a/yatemath.h b/yatemath.h
index 3e9f8d88..2cd9c21d 100644
--- a/yatemath.h
+++ b/yatemath.h
@@ -1074,16 +1074,18 @@ public:
      * @param func Pointer to function who appends the object to a String
      *  (0 to dump all available from offset)
      * @param sep Vector elements separator
+     * @param fmt Optional format to use
      * @return Destination string address
      */
-    String& dump(String& buf, String& (*func)(String& s, const Obj& o, const char* sep),
-	const char* sep = ",") const {
+    String& dump(String& buf,
+	String& (*func)(String& s, const Obj& o, const char* sep, const char* fmt),
+	const char* sep = ",", const char* fmt = 0) const {
 	    const Obj* d = data();
 	    if (!(d && func))
 		return buf;
 	    String localBuf;
 	    for (const Obj* last = end(d,length()); d != last; ++d)
-		(*func)(localBuf,*d,sep);
+		(*func)(localBuf,*d,sep,fmt);
 	    return buf.append(localBuf);
 	}
 
@@ -1099,23 +1101,24 @@ public:
      * @param linePrefix Prefix for new lines. Empty string to use the suffix
      * @param suffix String to always add to final result (even if no data dumped)
      * @param sep Vector elements separator
+     * @param fmt Optional format to use
      * @return Destination string address
      */
     String& dump(String& buf, unsigned int lineLen,
-	String& (*func)(String& s, const Obj& o, const char* sep),
+	String& (*func)(String& s, const Obj& o, const char* sep, const char* fmt),
 	unsigned int offset = 0, const char* linePrefix = 0,
-	const char* suffix = "\r\n", const char* sep = ",") const {
+	const char* suffix = "\r\n", const char* sep = ",", const char* fmt = 0) const {
 	    const Obj* d = data();
 	    if (!(d && func))
 		return buf.append(suffix);
 	    if (TelEngine::null(linePrefix))
 		linePrefix = suffix;
 	    if (!lineLen || TelEngine::null(linePrefix))
-		return dump(buf,func,sep) << suffix;
+		return dump(buf,func,sep,fmt) << suffix;
 	    String localBuf;
 	    for (const Obj* last = end(d,length()); d != last;) {
 		String tmp;
-		(*func)(tmp,*d,0);
+		(*func)(tmp,*d,0,fmt);
 		if (++d != last)
 		    tmp << sep;
 		offset += tmp.length();
@@ -1536,18 +1539,22 @@ public:
      * @param buf Destination string
      * @param val Value to dump
      * @param sep Optional separator
+     * @param fmt Format to use ("%g%+gi" if not given)
      * @return Destination string address
      */
-    static String& dumpComplex(String& buf, const Complex& val, const char* sep = 0);
+    static String& dumpComplex(String& buf, const Complex& val, const char* sep = 0,
+	const char* fmt = 0);
 
     /**
      * Dump a float number to a String
      * @param buf Destination string
      * @param val Value to dump
      * @param sep Optional separator
+     * @param fmt Format to use ("%g" if not given)
      * @return Destination string address
      */
-    static String& dumpFloat(String& buf, const float& val, const char* sep = 0);
+    static String& dumpFloat(String& buf, const float& val, const char* sep = 0,
+	const char* fmt = 0);
 };