CODEWITHSUNDEEP
vb.netstring
Quang Nguyen
Quang Nguyen

Reputation: 19

IndexOf returns -1 when it should return 0

I'm having a weird problem with the IndexOf function: 

"strcat".IndexOf("st")

returned -1 

"strcat".IndexOf("str")

returned 0

Can anyone explain why that happened?

Upvotes: 0

Views: 154

Answers (1)

TnTinMn
TnTinMn

Reputation: 11801

It may be related to your system's current culture. Based on your name, I assumed Vietnamese.

System.Threading.Thread.CurrentThread.CurrentCulture = New Globalization.CultureInfo("vi-VN")
Dim i1 As Int32 = "strcat".IndexOf("st")
Dim i2 As Int32 = "strcat".IndexOf("str")
Dim i3 As Int32 = "strcat".IndexOf("st", System.StringComparison.InvariantCulture)
Dim i4 As Int32 = "strcat".IndexOf("str", System.StringComparison.InvariantCulture)

yields: i1 = -1, i2 = 0, i3 = 0, i4 = 0

Edited to this address question posed in the comments section.

How does this happen? I don't see anything the culture would change?

To answer this you should refer to the documentation for the method. see: String.IndexOf Method (String)

The relevant information is:

This method performs a word (case-sensitive and culture-sensitive) search using the current culture. The search begins at the first character position of this instance and continues until the last character position.

A given culture has its own rules for what is considered "common knowledge/pratice". You should not assume that what you consider normal is normal in a different culture. This is reason that the methods that perform comparisons allow you to specify a culture to define the rules used to perform the comparison.

This does not apply only to strings, but also dates.

The most famous programming conundrum is: Does your program pass the turkey test? Also known as the "Turkish-I problem". These are terms that you can research for more information.

Upvotes: 5

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