string-concatenation

问题 Why doesnt this throw an exception dont understand, obj is null object obj = null; Console.WriteLine("Hello World " + obj); 回答1: This compiles to Console.WriteLine(String.Concat("Hello World ", obj)); The String.Concat method ignores null parameters. It's defined like this: (From the .Net reference source) public static String Concat(Object arg0, Object arg1) { if (arg0==null) { arg0 = String.Empty; } if (arg1==null) { arg1 = String.Empty; } return Concat(arg0.ToString(), arg1.ToString()); }

问题 Why doesnt this throw an exception dont understand, obj is null object obj = null; Console.WriteLine("Hello World " + obj); 回答1: This compiles to Console.WriteLine(String.Concat("Hello World ", obj)); The String.Concat method ignores null parameters. It's defined like this: (From the .Net reference source) public static String Concat(Object arg0, Object arg1) { if (arg0==null) { arg0 = String.Empty; } if (arg1==null) { arg1 = String.Empty; } return Concat(arg0.ToString(), arg1.ToString()); }

问题 How can I concatenate rows in select query? (in Advantage Data Architect) I tried run the following scripts: The first script: declare @str string; set @str = ''; select @str = @str + field_1 from my_table1 But I get a result where all rows contain "false", like this picture: Second script: declare @str string; select @str = coalesce(@str + ', ','') + field_1 from my_table1 This time, all rows are empty (note: the field from "my_table1" is not null). Picture: I tried to search the solution on

问题 How can I concatenate rows in select query? (in Advantage Data Architect) I tried run the following scripts: The first script: declare @str string; set @str = ''; select @str = @str + field_1 from my_table1 But I get a result where all rows contain "false", like this picture: Second script: declare @str string; select @str = coalesce(@str + ', ','') + field_1 from my_table1 This time, all rows are empty (note: the field from "my_table1" is not null). Picture: I tried to search the solution on

问题 How can I concatenate rows in select query? (in Advantage Data Architect) I tried run the following scripts: The first script: declare @str string; set @str = ''; select @str = @str + field_1 from my_table1 But I get a result where all rows contain "false", like this picture: Second script: declare @str string; select @str = coalesce(@str + ', ','') + field_1 from my_table1 This time, all rows are empty (note: the field from "my_table1" is not null). Picture: I tried to search the solution on

问题 I have a model called Lines. On it I have a address class that contains a number of strings, i.e.: public string ReferenceKey { get; set; } public string Country { get; set; } public string County { get; set; } public string Postcode { get; set; } public string PremisesName { get; set; } public string PremisesName { get; set; } I get information back from a webservice call to an outside party and then populate these fields with the returned data - note in some cases they may not return

问题 This question already has answers here : Concatenating strings in bash overwrites them (4 answers) Closed 2 years ago . My bash code file.sh : username=$1 pkgpath="/home/${username}_tmp.txt" echo $username echo $pkgpath Now running the script with the command bash file.sh abc should produce the result : abc /home/abc_tmp.txt But the output I'm getting is : abc _tmp.txtc Can someone explain why is this behavior occurring and how to obtain the desired result ? EDIT I'd like to mention that

问题 I've already searched for my problem, but most of the examples (if not all), have to deal with only one or two tables with a one-to-many relationship between them. So, here goes my scenario: My first table is: OrderID Quantity Price ---------------------------------- 18 1000.00 160.00 19 1000.00 40.00 22 1000.00 40.00 23 100.00 500.00 24 10.00 50.00 My second table is: ExtrasID Name ------------------- 1 Value 1 2 Value 2 3 Value 3 4 Value 4 5 Value 5 I have a many-to-many relationship

问题 I am trying to group by a dataframe on one column, keeping several columns from one row in each group and concatenating strings from the other rows into multiple columns based on the value of one column. Here is an example... df = pd.DataFrame({'test' : ['a','a','a','a','a','a','b','b','b','b'], 'name' : ['aa','ab','ac','ad','ae','ba','bb','bc','bd','be'], 'amount' : [1, 2, 3, 4, 5, 6, 7, 8, 9, 9.5], 'role' : ['x','y','y','x','x','z','y','y','z','y']}) df amount name role test 0 1.0 aa x a 1

问题 This question already has answers here : Closed 8 years ago . Possible Duplicate: How do I concatenate strings in Objective-C? Firstly, the platform is iPhone and label.text changes the label displayed. Consider this scenario: I've an array of integers. And I want to display it on the screen. Here's my take on it: -(IBAction) updateText: (id)sender { int a[2]; a[0]=1; a[1]=2; a[2]=3; for (int i=0; i<=10;i++) label.text = [NSString stringByAppendingString: [NSString stringWithFormat: @"%i", a