C＃字符串浮动

Question

When I convert a string to a float I get my answer plus a bunch of junk decimals. How do I fix this? Is this floats error I'm seeing?

string myFloat = "1.94";
float f = float.Parse(myFloat);

It needs to be a float for database reasons ...

By junk I mean 1.94 turns into: 1.94000005722046

Answer 1

The problem is that you can't use float / double if you want a precise representation of your parsed number. In case you need that you must use decimal . For money amounts its almost always required to use decimal . So keep that in mind.

Please read about how floating point numbers are represented internally: http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html

How 1.94 is represented internally by a float can be tested in this calculator: http://pages.cs.wisc.edu/~rkennedy/exact-float?number=1.94

As you see its 1.940000057220458984375 .

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Databases support the decimal datatype:

• Oracle offers DECIMAL: http://docs.oracle.com/javadb/10.6.2.1/ref/rrefsqlj15260.html
• SQL Server offers DECIMAL: http://msdn.microsoft.com/de-de/library/ms187746.aspx
• MySQL offers DECIMAL: https://dev.mysql.com/doc/refman/5.1/en/fixed-point-types.html

Answer 2

You can change it to a double to get a more accurate representation but if you need it exactly You cannot fix this this is how floats are represented in computers. If you use the decimal data type you will get an exact representation.

string myFloat = "1.94";
decimal f = decimal.Parse(myFloat);

And then do the conversion to double when you store it to the database. You could still get some noise in the database. The only way to be sure to get rid of this is to use numeric in the database.