I don't know the origin of the specification although I suspect it may have come from or been influenced by FORTRAN (or maybe COBOL although I have forgotten anything I knew about COBOL). FORTRAN has always done it this way and it predates C and C++ by a few years (doesn't make it right, I know): that is, the "15" is the field width and the ".8" is the number of decimal digits. It sort of makes sense. In the %04d case 4 is the field width with perhaps an implied .0 since integers by definition have no decimal part. You can, of course, specify %04.0lf and will get an integer representation of a double value with a field width of 4. Larry ----- Original Message ----- From: "Alfredo Correa" Cc: Sent: Thursday, September 30, 2010 9:33 PM Subject: Re: [Boost-users] [format] print float number with fixed number of decimals *and* integer digits On Thu, Sep 30, 2010 at 5:41 PM, Larry wrote:

I believe if you use something like "%015.8lf" you will get more of what you want. I always think that the .8 is the number of digits to the right of decimal and the 15 is the entire field width (including sign, any leading zero digits, any digits to the left of the decimal, the decimal point, and digits to the right of decimal point).

Right, I though that the number before the dot . was the number of integer digits not the total number of digits. std::cout<< boost::format("%015.8f") % d << std::endl; works, prints 000003.14150000 Thank you, Alfredo

For example:

double pi(3.141592);

format a("%015.8lf"); a % pi; printf("%s\n",a.str().c_str());

prints:

000003.14159200

Larry ----- Original Message ----- From: "alfC" To: Sent: Thursday, September 30, 2010 7:21 PM Subject: [Boost-users] [format] print float number with fixed number of decimals *and* integer digits

...

I always found the rules for printf formatting, which Boost.Format uses, cryptic. I usually find the right combination by trial and error. In this case I want to print decimal numbers with both fixed number of integer digits and decimal digits. How can I do this with Boost.Format.

#include #include<iostream> int main(){ int i = 2; std::cout << boost::format("%04i") % i << std::endl; //prints 0002, ok! double d = 3.1415; std::cout<< boost::format("%04.8f") % d << std::endl; // ^ prints 3.14150000, // want 0003.14150000 //(or even ' 3.14150000') //(or even ' 3.1415 ') return 0; }

Thank you, Alfredo

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