[Coin-discuss] Problem with MPS export / MSVC

[Matthew Saltzman]

On Thu, 25 Mar 2004, Jörg Herbers wrote:

> I encountered a problem when exporting an mps file via CoinMpsIO. I work on
> Microsoft Visual Studio .NET 2003 which handles printf format specification
> flags somewhat different from e.g. the gcc compiler. The problem is that
> large "infinity" upper bounds are exported as "2.147484e+00", i.e. the
> exponent is 0. CoinMpsIO::writeMps() takes the minimum over the given upper
> bound and INT_MAX (2147483647). convertDouble() converts this to a string,
> using format specification "%12.7g". The resulting string is cut after 12
> characters according to the MPS specification for the BOUNDS section. But
> while gcc converts INT_MAX into 2.147484e+09, MS VC7 (and equally MS VC6)
> converts it into 2.147484e+009, and the final "9" at position 12 will be cut
> afterwards. The Microsoft documentation says that the exponent will always
> be typeset with three digits while gcc uses two digits for exponents <100. I
> don’t know if the C++ standard defines a "correct" behaviour.

printf() is a C function.  According to Harbison & Steele 4th ed., "The
number of exponent digits is the same for all values and is the maximum
needed to represent the range of the implementation's floating-point
types."

That would seem to indicate that gcc is in the wrong on this point.  On
the other hand, it also means that field width 12 is not wide enough to
hold DBL_MAX (1.797693e+308) to seven digits of precision anyway.  If the
field width is forced to be 12 for MPS files, then the most we can
guarantee is six digits of precision ("%12.6g" or just "%12g").

>
> I have solved the problem in my COIN code, but I would clearly prefer a
> general solution. Several ways are viable: On the one hand, the format
> specifications could generally be changed to "%12.6g". On the other hand,
> there could be a specific solution for the Microsoft compiler, e.g. by the
> above reduction of significant digits or by a manipulation of the resulting
> string, e.g. by something like
>
> #if defined(_MSC_VER)
>     if ((outputValue[9] == '+') && (outputValue[10] == '0'))
>       strcpy(&(outputValue[10]), &(outputValue[11]));
> #endif
>
> I would be very glad if you could integrate a fix into the code.
>
> Thanks a lot,
> Jörg
>
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-- 
		Matthew Saltzman

Clemson University Math Sciences
mjs AT clemson DOT edu
http://www.math.clemson.edu/~mjs