This is about output of real values (float, double, ...) in exponential format and output of not a number and infinity. My concern is that in C++, the output differs from one compiler/machine to another. It would be very nice if boost::format could garantee the same output on every computer. For example, the following code gives the following output on various machines (using boost 1.33.1): std::cout << format("%1% ") % 1e12 ; std::cout << format("%1% ") % std::numeric_limits<double>::quiet_NaN() ; std::cout << format("%1% ") % std::numeric_limits<double>::infinity() ; std::cout << format("%1%") % (-std::numeric_limits<double>::infinity()) ; The output on cygwin (compiled with g++ 3.4.4) is: 1e+12 nan inf -inf The output on windows (compiled with g++ 3.4.4 on cygwin with flag -mno-cygwin) is: 1e+012 1.#QNAN 1.#INF -1.#INF The output on Tru64 (compiled with g++ 3.4.4) is: 1e+12 NaNQ INF -INF This makes difficult to check if the programs do the same on various machines as soon as tests include output of numbers. Here, I cite section 7.19.6.1 The fprintf function of standard "Programming languages — C" ISO/IEC 9899:1999(E): The effect of the printf function in C is descibed as: A double argument representing an infinity is converted in one of the styles [-]inf or [-]infinity — which style is implementation-defined. A double argument representing a NaN is converted in one of the styles [-]nan or [-]nan(n-char-sequence) — which style, and the meaning of any n-char-sequence, is implementation-defined. A double argument representing a floating-point number is converted in the style [-]d.ddd e±dd, ... The exponent always contains at least two digits, and only as many more digits as necessary to represent the exponent. Could we have the same in C++: 1. 2 digit in the exponent and more only if needed 2. a standard format for not a number and infinity: nan and inf. (They are roughtly implementation defined in C!) In the C++ standard "Programming languages — C++" ISO/IEC 14882:2003(E), the only reference to printf is in 27.8.2 C Library files where we can find the list of functions in cstdio. Also using cout, there is no description of how to handle NaN, infinity and the number of digits in the exponents. The function should be described in the previous C standard "Programming languages – C" ISO/IEC 9899:1990 which I do not have. Thanks, F. Bron Avis : Ce message et toute pièce jointe sont la propriété d'Alcan et sont destinés seulement aux personnes ou à l'entité à qui le message est adressé. Si vous avez reçu ce message par erreur, veuillez le détruire et en aviser l'expéditeur par courriel. Si vous n'êtes pas le destinataire du message, vous n'êtes pas autorisé à utiliser, à copier ou à divulguer le contenu du message ou ses pièces jointes en tout ou en partie. Notice: This message and any attachments are the property of Alcan and are intended solely for the named recipients or entity to whom this message is addressed. If you have received this message in error please inform the sender via e-mail and destroy the message. If you are not the intended recipient you are not allowed to use, copy or disclose the contents or attachments in whole or in part.