Why are doubles added incorrectly in a specific Visual Studio 2008 project?
c++, visual-c++, visual-studio, visual-studio-2008
Solution
The only thing I can think of is perhaps you are linking against a library or DLL which has modified the CPU precision via the control word.
Have you tried calling `_fpreset()` from `float.h` before the problematic computation?
Problem
Trying to port java code to C++ I've stumbled over some weird behaviour. I can't get double addition to work (even though compiler option /fp:strict which means "correct" floating point math is set in Visual Studio 2008). ``` double a = 0.4; /* a: 0.40000000000000002, correct */ double b = 0.0 + 0.4; /* b: 0.40000000596046448, incorrect (0 + 0.4 is the same). It's not even close to correct. */ double c = 0; float f = 0.4f; c += f; /* c: 0.40000000596046448 too */ ``` In a different test project I set up it works fine (/fp:strict behaves according to IEEE754). Using Visual Studio 2008 (standard) with No optimization and FP: strict. Any ideas? Is it really truncating to floats? This project really needs same behaviour on both java and C++ side. I got all values by reading from debug window in VC++. Solution: _fpreset(); // Barry Kelly's idea solved it. A library was setting the FP precision to low.