我如何更改文本文件中的数据类型以读取字符串而不是整数（C ++ / CLI，OleDb）？

Question

My goal is it to read from a text file. This text file contains different columns and rows for each value. I can read the file as long as I don't change the datatype that windows set on its own. But I do not want the "plz" and "nr" column to be numbers (integers) but a text (String) value because a plz could contain values like "01979" and the nr could contain something like "4a". As a number the starting zero would be lost and this way something like a postcard would never reach its intended destination.

This way I need to change the datatype in a "schema.ini" file. But it doesn't work. I think I make some mistakes and do not follow the tutorial the way I need to do: "Schema.ini File"

Everytime I tried to read a String I got an Exception because it still want to read an Int32-values that I would need to convert into a string.

I did name the file "kunde.txt"

knr|nachname|vorname|plz|ort|strasse|nr
1|Müller|Johan|12345|Muster|Musterstr|1
2|Kummer|Freude|23456|Feeling|Gefühlswelt|4a

Col 0 = knr, 1 = nachname, 2 = vorname, 3 = plz, 4 = ort, 5 = strasse, 6 = nr

con->ConnectionString =
    "Provider=Microsoft.JET.OLEDB.4.0;" +
    "Data Source=D:/C++/Quellen;" +
    "Extended Properties=text";
// ....
meineKunden->CommandText =
    "SELECT knr, nachname, vorname, plz, ort, strasse, nr " +
    "FROM kunde.txt ";
// ....
String ^ str;
while(reader->Read()){
    str += Convert::ToString(reader->GetInt32(0));
    str += " ";
    str += reader->GetString(3);
    str += " ";
    str += reader->GetString(6);
    str += "\r\n";
}
this->txb_Insert->Text = str;

My schema.ini

[kunde.txt]
ColNameHeader=True  
Format=Delimited(|) 
3=plz Char Width 5
6=nr Char Width 10

I did try with "Col3" instead of "3". I did use "Text" rather tan "Char", and I did even attempted it without Width. But everytime I got the same failure message. Even if i use 4 or 7 ... since I am not sure how it will be counted in the ini / txt file.

Exception:

System.InvalidCastException: Die angegebene Umwandlung ist ungültig.
bei System.Data.OleDb.ColumnBinding.ValueString()
bei System.Data.OleDb.OleDbDataReader.GetString(Int32 ordinal)

The exception is calls already by str += reader->GetString(3) If I am correct column 3 contains plz, this way.

Could someone please say what I do understand wrong with the schema.ini file? Since I could read the file without mistakes as long as I doesn't try to specific change the datatype in some columns the problems need to be with the ini file. At least I think so.

EDIT: I did change my ini-file to:

[kunde.txt]
ColNameHeader=True  
Format=Delimited(|) 
Col1="knr" Integer
Col2="nachname" Text
Col3="vorname" Text
Col4="plz" Text
Col5="ort" Text
Col6="strasse" Text
Col7="nr" Text

Now it works for "plz" but the exception is called in the last row, when I call the "nr". WTF?

Answer 1

You have to maintain that the way you read data from the file suits the way it's written in .

So if the file in not written by you and you have to use it,try to know if it has a specific structure (for ex: fixed length record delimited fields , fixed length record fixed length fields.. etc) and use a way that suits this structure to read it.

Also try to know how fields of records are written in details because the way you read is the same as you write .