double type precision in VC7

K

kingkong

Hi,

I am porting some code from VC6 to .net 2003 VC7.1. The code is to do
yield curve interpolation, therefore precision is important. I have
found some strange behavior in the VC7.1 environment. Allow me to show
the problem:

....
double_v strikes;
strikes.reserve(11);
strikes.push_back(0.00750);
strikes.push_back(0.01965);
strikes.push_back(0.02000);
strikes.push_back(0.02076);
strikes.push_back(0.05000);
strikes.push_back(0.09000);
....
When I examine the values in strikes in the VC6 debugger, I can see the
exact number that I inserted. In the VC7.1 debugger, some of the
numbers in strikes are different by a very small fraction. The numbers
shown in the VC71 debugger are:

strikes._M_start,6
[0] 0.0074999999999999997
[1] 0.019650000000000001
[2] 0.020000000000000000
[3] 0.020760000000000001
[4] 0.050000000000000003
[5] 0.089999999999999997

I am using stlport4.6.2 which I don't think it is the cause of the
problem. I am new to the MS environment, even newer to the VC71 world.
My question is why these 2 environments are different and how to work
around it.

Any advice will be greatly appreciated.

MK
 
C

Carl Daniel [VC++ MVP]

kingkong said:
Hi,

I am porting some code from VC6 to .net 2003 VC7.1. The code is to do
yield curve interpolation, therefore precision is important. I have
found some strange behavior in the VC7.1 environment. Allow me to show
the problem:

...
double_v strikes;
strikes.reserve(11);
strikes.push_back(0.00750);
strikes.push_back(0.01965);
strikes.push_back(0.02000);
strikes.push_back(0.02076);
strikes.push_back(0.05000);
strikes.push_back(0.09000);
...
When I examine the values in strikes in the VC6 debugger, I can see the
exact number that I inserted. In the VC7.1 debugger, some of the
numbers in strikes are different by a very small fraction. The numbers
shown in the VC71 debugger are:

strikes._M_start,6
[0] 0.0074999999999999997
[1] 0.019650000000000001
[2] 0.020000000000000000
[3] 0.020760000000000001
[4] 0.050000000000000003
[5] 0.089999999999999997

I am using stlport4.6.2 which I don't think it is the cause of the
problem. I am new to the MS environment, even newer to the VC71 world.
My question is why these 2 environments are different and how to work
around it.

Any advice will be greatly appreciated.
Click to expand...

You're being misled into believing that you have different problems in VC7
that you had in VC6. Please read

http://docs.sun.com/source/806-3568/ncg_goldberg.html

before you do anything else.

The difference is simply in how the debugger displays the double data type.
VC6 rounds to 6 (or so) digits, while VC7 doesn't.

-cd
 
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