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[英]what is the difference between String.Concat ,string.format and +?
[英]What is the difference between String.Format and Composite String in C#?
這兩種語法有什么區別?
有沒有必須使用String.Format而不是復合字符串的情況?
Console.WriteLine("{0:d} {0:t}",DateTime.Now);
Console.WriteLine(String.Format("{0:d} {0:t}",DateTime.Now));
它們之間沒有任何區別,因為
Console.WriteLine("{0:d} {0:t}",DateTime.Now);
這將通過此重載函數調用String.Format
函數。
public virtual void WriteLine(String format, Object arg0)
{
WriteLine(String.Format(FormatProvider, format, arg0));
}
我剛剛注意到必須使用String.Format或插值字符串而不是普通復合字符串的情況。
SqlConnection myConnection = new SqlConnection("......");
SqlDataAdapter myDataAdapter1 = new SqlDataAdapter("SELECT userAddress FROM tblUserData WHERE userName = '" + userName + "'", myConnection);
SqlDataAdapter myDataAdapter2 = new SqlDataAdapter("SELECT userAddress FROM tblUserData WHERE userName = '{0}'", userName, myConnection);
SqlDataAdapter myDataAdapter3 = new SqlDataAdapter(String.Format("SELECT userAddress FROM tblUserData WHERE userName = '{0}'", userName), myConnection);
SqlDataAdapter myDataAdapter4 = new SqlDataAdapter($"SELECT userAddress FROM tblUserData WHERE userName = '{userName}'",myConnection);
由於參數不正確,myDataAdapter2無法正常工作。
(是的,通常,SELECT語句被賦值給字符串變量。)
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