Converting string to double correctly

Question

I am writing a program in c# and have encountered an annoying little problem. I need to convert fields from dataGridView control to double in order to store them in database. However, it doesn't convert correctly.

The original values in dataGridView use comma (,) for decimal point separation.

Here's the original code:

double number = Convert.ToDouble(dataGridView1.Rows[row].Cells[1].Value)

The cell is textbox type. By using this method 12,3 becomes 12,3E+14

For some unknown reasons, the converter multiplies the number by 10 with the power 14.

After reading some questions, I stumbled upon another possible solution

double number = Convert.ToDouble(dataGridView1.Rows[row].Cells[1].Value, CultureInfo.CurrentCulture);

Still the same result. 12,3 -> 12,3E+14

double number = Convert.ToDouble(dataGridView1.Rows[row].Cells[1].Value.ToString(), CultureInfo.CurrentCulture);

This gets even more interesting. Instead of 12,3 i'm getting 123

Am I missing something? Is there a simple solution to all of this?

EDIT: just in case - the database field type is set to real and dataGridView cell is TextBox type, so the input is string type.

EDIT2: The thing I am trying to do is to load value (real) from database to DGV, save it to a different database table as real, then load the value from the newly written database table (real) and show it in another DGV. After writing the values from DGV1 to database, their type is Single. After writing them to database the 2nd time, however, the value becomes String type, even though i did no changes to it. Could this be what's distorting the conversion values? I mean the 1st time they show up as 12,3E+14 instead of 12,3. I could just divide them by Math.Pow(10, 14) to get the original value, but this is dirty practice :/

FINAL EDIT: Thank you all for your help, but the real problem in this case was my carelessness. As this program is being developed for quite a while, back when I was still getting used to c# syntax, I have included some variable type mix-ups, which has led me to having to review all the types in the code. Again, thank you all for help.

TL;DR - keep your variable types consistent.

The fact that you get a different result when calling `ToString()` on the cell's value suggests that the value is not of type `string`. Can you verify what the underlying type of `dataGridView1.Rows[row].Cells[1].Value` is? — user1620220, Dec 03 '14 at 19:03
The column in dataGridView is of type DataGridViewTextBoxColumn. How could it possibly be anything other than string? — TheMasterSoda, Dec 03 '14 at 19:15
According to the [documentation](http://msdn.microsoft.com/en-us/library/system.windows.forms.datagridviewtextboxcell(v=vs.110).aspx), a DataGridViewTextBoxCell's value is of type `Object`, meaning it could be anything. Finding out the runtime type will help determine why it is behaving the way it is. — user1620220, Dec 03 '14 at 19:20

Ric Gaudet · Answer 1 · 2014-12-03T20:31:42.833

2

If your CurrentCulture is, say, in the US, it will parse "1,23" as 123.

As Tigran noted, create a FormatProvider, or create a NumberFormatInfo. Here is an alternate solution, if you don't want/need to change the CurrentCulture defaults.

NumberFormatInfo provider = new NumberFormatInfo();
provider.NumberDecimalSeparator = ",";
double num = Convert.ToDouble("1,23", provider);

If this line of code gives you 123:

double number = Convert.ToDouble(dataGridView1.Rows[row].Cells[1].Value.ToString(), CultureInfo.CurrentCulture);

then this should give you 1.23:

NumberFormatInfo provider = new NumberFormatInfo();
provider.NumberDecimalSeparator = ",";
double number = Convert.ToDouble(dataGridView1.Rows[row]
.Cells[1].Value.ToString(),provider);

edited Dec 03 '14 at 20:31

answered Dec 03 '14 at 19:27

Ric Gaudet

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This method still returns wrong values: 12,3 turns to 12,3E+14 – TheMasterSoda Dec 03 '14 at 19:40
Looks like you have two problems to solve: converting your value to a string (from whatever type it is) and then properly displaying the number. – Ric Gaudet Dec 03 '14 at 20:26

Jeff Musser · Answer 2 · 2014-12-03T19:18:30.737

0

you could try calling the replace function on the string to replace , with a . then doing the conversion. Try this:

double number = Convert.ToDouble(dataGridView1.Rows[row].Cells[1].Value.ToString().Replace(",", "."));

edited Dec 03 '14 at 19:18

answered Dec 03 '14 at 19:07

Jeff Musser

121
5

Error 1 'object' does not contain a definition for 'Replace' and no extension method 'Replace' accepting a first argument of type 'object' could be found (are you missing a using directive or an assembly reference?) \Form1.cs 464 104 Application – TheMasterSoda Dec 03 '14 at 19:12
try Cells[1].Value.ToString().Replace() – Sandip Bantawa Dec 03 '14 at 19:14
@TheMasterSoda This means as user1620220 pointed out that the value in your Grid View is not a string. We need to know what type it is in order to determine what should be done. – juharr Dec 03 '14 at 19:15
@brykneval Program stops with error that the input string is not in the correct format. – TheMasterSoda Dec 03 '14 at 19:18
try adding .ToString() after Value – Jeff Musser Dec 03 '14 at 19:18
@Grant Winney how could it be anything else and how would i check it? – TheMasterSoda Dec 03 '14 at 19:18
@TheMasterSoda try my suggestion, if it isn't a string then using .ToString() will make it. – Jeff Musser Dec 03 '14 at 19:20
@Jeff Musser it still crashes at the same place, on the first encounter of a number with a decimal separator. – TheMasterSoda Dec 03 '14 at 19:29

score 0 · Answer 3 · edited May 23 '17 at 12:27

0

Have you try

double da = double.Parse(a, CultureInfo.InvariantCulture);

Here in similar kind of problem

they used it

C# convert string to double in locale

edited May 23 '17 at 12:27

Community

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answered Dec 03 '14 at 19:09

Praveen Shakkarval

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Tigran · Answer 4 · 2014-12-03T19:51:33.197

0

The first and second cases are identical, cause in both cases function uses CurrentCulture like a second parameter.

The third one is more interesting as you use: Convert.ToDouble(String) overload, which uses

the formatting conventions of the current thread culture.

which may defer from that one of your machine and else.

So like the first thing to do, imo, you can check if the current debugging (I immagine) thread culture is equal to that one of your machine, if not that makes a difference.

Consider that in "fr-FR" the decimal separator is "," where in "en-US" is ".". In order to correctly threat the known format of the data you get you need to provide custom FormatProvider and parse using it.

So in your case the code may look like:

 //assign expected separator
 NumberFormatInfo nf = new NumberFormatInfo();
 nf.NumberDecimalSeparator = ",";

 var val = dataGridView1.Rows[row].Cells[1].Value;
 double number = Convert.ToDouble(val, nf);

Should work for you.

edited Dec 03 '14 at 19:51

answered Dec 03 '14 at 19:16

Tigran

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I assume the "culture" should be "myCulture". In that case, I cannot change its parameters, because the instance is read-only. – TheMasterSoda Dec 03 '14 at 19:36
@TheMasterSoda: *it is* `myCulture`. what do you mean ? – Tigran Dec 03 '14 at 19:37
When trying to assign new decimal separator value to myCulture, program hangs with error "Instance is read-only" – TheMasterSoda Dec 03 '14 at 19:49
@TheMasterSoda: I updated answer to concrete working example. – Tigran Dec 03 '14 at 19:51
It still returns the 12,3E+14 instead of 12,3 – TheMasterSoda Dec 03 '14 at 19:56

Olivier Jacot-Descombes · Answer 5 · 2014-12-03T19:40:48.890

0

Since the Value property is of type object, it could contain a boxed double value already. In that case a cast would be sufficient:

double number = (double)dataGridView1.Rows[row].Cells[1].Value;

or, if the column is nullable, possibly

double? number = (double?)dataGridView1.Rows[row].Cells[1].Value;

Note that this does not involve a conversion, it just casts the value to its right type.

Try to output this in order to know the type of the value:

System.Diagnostics.Debug.WriteLine(
    dataGridView1.Rows[row].Cells[1].Value.GetType().Name);

And open the ouput window.

edited Dec 03 '14 at 19:40

answered Dec 03 '14 at 19:35

Olivier Jacot-Descombes

104,806
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It crashes with error "specified cast is not valid" – TheMasterSoda Dec 03 '14 at 19:45
so apparently, the type is Single – TheMasterSoda Dec 03 '14 at 19:50
If type is `single` either cast to single or `(double)(single)obj` if you need a double. Because first you need to cast the object to is "right" type and then you can convert it to double. – Olivier Jacot-Descombes Dec 03 '14 at 19:58
I tried Convert.ToDouble((Single)obj) and just using (Single), but for some reason it still shows as 12,3E+14 instead of 12,3. I'm starting to think I'll just have to divide it by 10^14 and be done with it. – TheMasterSoda Dec 03 '14 at 20:14
How do the values from the table get into the dgv exactly? – Olivier Jacot-Descombes Dec 03 '14 at 20:21

TheMasterSoda · Answer 6 · 2014-12-03T22:44:39.990

0

I have finally solved my problem. It appears, that even though C# has localization options, SQL doesn't.

Numbers were converting just fine, but SQL parsed queries wrong:

"INSERT INTO myTable VALUES ('2,5' , '3,1');

didn't work, but this did:

"INSERT INTO myTable VALUES ('2.5' , '3.1');

edited Dec 03 '14 at 22:44

answered Dec 03 '14 at 20:41

TheMasterSoda

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Converting string to double correctly

6 Answers6