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DateTime.Parse works in c# console app but not asp.net

I have written a C# console application that after all of it's processing outputs a DateTime to disk. It does this like so:
writer.WriteLine(myDateTime).
This same console appication has no problems with using the following to read this DateTime back:
DateTime.Parse(reader.ReadLine())
However, upon attempting to use the following code in my separate Asp.Net program I recieve an error saying that my string is not a valid DateTime which is odd to say the least.
StreamReader reader = new StreamReader(#"D:\InformerReports\Archive\ReliabilityData\StartTime.hist");
string dateString = reader.ReadLine();
return DateTime.Parse(dateString);
I have checked and the string it is reading in is 10/25/2016 12:00:00 AM.
I have also attempted to use return DateTime.ParseExact(dateString, "dd/MM/yyyy hh:mm:ss tt",null) but this returns the same error.
I can't seem to fathom why identical code performed on the same file works in one case and not the other. I'd appreciate some help.

I guess the culture of the server is different from the machine you are testing from.
The correct format you have to use seems to be:
return DateTime.ParseExact(dateString, "MM/dd/yyyy hh:mm:ss tt", null)
// 10/25/2016 12:00:00 AM

As an add-on to the previous answers.
To avoid the differing cultures across clients you can set the site culture in the global.asax files Application_BeginRequest method like below:
Threading.Thread.CurrentThread.CurrentCulture = new System.Globalization.CultureInfo("fr-FR");
Threading.Thread.CurrentThread.CurrentUICulture = new System.Globalization.CultureInfo("fr-FR");
This will force the above specified culture for each user accessing the site.
I am not sure if there are drawbacks to doing it this way, but this solved my issue in the past.

Azure culture-specific month/day formatting different than localhost

I'm running into a very strange issue where the "month/day" standard date format as specified on https://msdn.microsoft.com/en-us/library/az4se3k1(v=vs.110).aspx is rendering differently on my local machine than it is on my azure cloud services and websites.
The culture in this case that is rendering differently is "en-AU". For the date of 2017-05-04 it should render as 4 May and on my local machine it does exactly that. On our website (azure cloud service) and our API (azure website) it renders as May 4. The strange part is that if I use the "short date pattern" it renders as 04/05/2017 on both azure/local. So this seems to be specific only to the "month/day" pattern.
I've tried setting
var culture = new CultureInfo("en-AU");
Thread.CurrentThread.CurrentCulture = culture;
Thread.CurrentThread.CurrentUICulture = culture;
and the formatting code is
string.Format(new CultureInfo("en-AU"), "Until {0:M} {0:yyyy}", endDate);
I'm wondering if its possible that the version of some culture definition is different in Azure than it is on my local machine? To my knowledge they are both running .net 4.5. I've added log statements in the code so I can confirm that the culture is set correctly on the line that the code runs, but for some reason, it is just outputting a different value in Azure than it does locally.

I have used both "en-AU" and "en-ZA" culture in both local and Azure environments.Unfortunately,I did not face the issue that you have mentioned in your question in both environments.
It seems the date format that you are getting is US format which might be due to the fact that azure data center that you are using to host your application is based in USA and your date is formatted to that culture.Anyway,give a try to format the date like :
var currentCulture = new CultureInfo("en-AU");
var formattedDate = DateTime.Now.ToString("G",currentCulture);
For the South African culture,try the following:
var currentCulture = new CultureInfo("en-ZA");
var formattedCurrency = currency.ToString("C", currentCulture);
//currency = 100000 then formattedCurrency => R 100 000,00
Good luck ..!!!

Inconsistent DateTime conversion behaviour in .NET Web Service

Problem
I've a Windows app syncs with the Server using SharePoint hosted Web Services.
When the app syncs to the server using LAN (goes through an internal Proxy server) all the DateTime formats are in dd/MM/yyyy format (which is how it is intended to be)
However, when the app syncs over 4G,all DateTime formats are in MM/dd/yyyy format.
This happens for all data inbound and outbound.
Server
Windows Server 2012 with SharePoint 2013 hosting SOAP services
Region: Singapore
Format: English (Singapore)
Client
Windows 10 tablet app
Region: Singapore
Format: English (Singapore)
Other information:
1. It is the same tablet being used on both WiFi and 4G, so we can rule
out 2 tablets having different regional settings.
2. I've verified that the Windows 10 app passes the formats correctly and it is the server that behaves differently over WiFi and 4G.
3. I beleive that the issue is caused by .NET itself and not because of SharePoint. However, I don't want to rule it out as I'm not sure of the actual cause. Please comment if you require any further information if you feel that it is caused because of SharePoint
Snippets:
I've skipped the using statements and SPWeb statements in the snippet to keep it simple. And the LastModifiedTime field in the SPList of type DateTime and not single line text.
Model
public class Record
{
public string ID {get; set}
public string ModifiedDateTime {get; set;} //Don't ask why it is not a DateTime object. It was too late by the time I took over
}
Web Service
public class WebService : IWebService
{
public List<Record> GetUpdates(string lastModifiedTime)
{
SPQuery query= QueryBuilder.GetUpdateQuery(lastModifiedDateTime);
SPList spRecordList = spWeb.Lists["Record"];
SPListItemCollection results = spRecordList.GetItems(query);
List<Record> records = new List<Record>();
foreach(SPListItem spRecord in results)
{
Record record = new Record();
record.ID = spRecord.ID.ToString();
record.ModifiedDateTime = Convert.ToString(spRecord["LastModifiedTime"]);
//1 June 2015 would return as 01/06/2015 in WiFi but 06/01/2015 on 4G
records.Add(record);
}
return records;
}
public Record CreateOrUpdateRecord(Record record)
{
SPListItem spRecord = null;
SPList spRecordList = spWeb.Lists["Record"];
if(string.IsNullOrEmpty(record.ID))
{
spRecord = spRecordList.AddItem();
record.ID = spRecord.ID.ToString();
}
else
{
spRecord = spRecordList.GetItemByID(record.ID);
}
DateTime modified = Convert.ToDateTime(record.Modified);
spRecord["LastModifiedTime"] = modified;
/*
Say ModifiedDateTime is 1 June 2015.
Then on WiFi, modified = 01/06/2015
On 4G, modified = 06/01/2015
*/
return record;
}
}
Now, I've fixed the problem by using format strings when converting between string and DateTime and vice-versa. So more or less, I've got it working for now.
So my question here is, what is the reason behind this behaviour? If possible, please cite links to documentation or references to any other sources that explain this behaviour
Is it possible that the server infers the culture info from the request header? I've always thought that the DateTime.Parse()/Convert.ToDateTime() always got the defaults from the regional settings of the machine it runs on.

First of all, a DateTime does not have any implicit format. It just have date and time values. Format concept only applies when you get it textual (string) representation. I strongly suggest to change this data type from string to DateTime if you can that returns by web service.
I've verified that the Windows 10 app passes the formats correctly and
it is the server that behaves differently over WiFi and 4G
There is no such a thing. Parsing string to DateTime or vice versa does not depends on how you connected to internet. It is all about culture settings.
Since you use it as;
DateTime modified = Convert.ToDateTime(record.Modified);
This code will use CurrentCulture settings by default where it's located. Since you said;
It is the same tablet being used on both WiFi and 4G, so we can rule
out 2 tablets having different regional settings
One regional settings parse your string as a 6 January and the other settings parse your string as 1 June. That's too normal. Looks like one setting uses dd/MM/yyyy format and the other one uses MM/dd/yyyy.
As a solution, you can use DateTime.ParseExact method to specify exact culture that matches with your string. Or you can equalize regional settings on both tablet.
For example;
DateTime dt = DateTime.ParseExact("01/06/2015", "dd/MM/yyyy", CultureInfo.InvariantCulture);
will parse as 1 June 2015 but
DateTime dt = DateTime.ParseExact("01/06/2015", "MM/dd/yyyy", CultureInfo.InvariantCulture);
will parse as 6 January 2015.

MVC3: Submit string - parse fails on IE and Chrome

I have an issue with the submitted form information. Decimal parsing fails when I try to parse a string returned through Interner Explorer or Chrome but not on Firefox or Safari. The strings looks exactly the same in Visual Studio. I made this debugging bit:
var asd3 = collection["formValue"]; // Get it from the FormCollection
var asd4 = asd3.Replace(",", "."); // Change the punctuation
var asd5 = Decimal.Parse(asd4); // Make the string into a decimal
var asd6 = Math.Round(asd5, 1); // Round it
It fails on asd5 when trying to parse the decimal out of asd4 with the error: Input string was not in a correct format.
Here's an image of the strings. Top is Firefox and below Internet Explorer.
What on earth could be the problem here?

What on earth could be the problem here?
Culture.
In your debugger inspect the value of Thread.CurrentThread.CurrentCulture and you will see differences between your browsers.
If you have a different culture set in your browser this culture will be used by ASP.NET when parsing values especially if you haven't explicitly specified the culture in your web.config:
<globalization culture="en-US" uiCulture="en-US" />
If this is set to auto then the browser culture will be used.
Another possibility is to force invariant culture when parsing to ensure that . (dot) will be the decimal separator.
var asd5 = Decimal.Parse(asd4, CultureInfo.InvariantCulture);

DateTime parsed differently in different environments?

I am inserting some data into a SharePoint list (via web services) and on my local machine I set a date field like this (hard coded in this example)
<Field Name='TimeOnScene'>" + DateTime.Parse("13/12/2011 1:00").ToString("yyyy-MM-ddTHH:mm:ssZ") + "</Field>
and it works fine on my local machine, but if I publish it to our web host and run the exact same code I get
{"Message":"String was not recognized as a valid DateTime.","StackTrace":"
//
//
System.DateTimeParse.Parse(String s, DateTimeFormatInfo dtfi, DateTimeStyles styles)\r\n at System.DateTime.Parse(String s)\r\n "ExceptionType":"System.FormatException"}
How is this possible?
Thanks in advance.
Edit:
we also moved from host to another two weeks ago and never had this issue before.

Use DateTime.ParseExact instead of Parse, the converting will be like the following code.
CurDate = DateTime.ParseExact(YourDateString, "dd/MM/yyyy hh:mm", System.Globalization.CultureInfo.CurrentCulture, System.Globalization.DateTimeStyles.None)

The host could have different local in set on there machine. in the documentation
The string s is parsed using formatting information in the current DateTimeFormatInfo object, which is supplied implicitly by the current thread culture.