Informant | node based server monitor to get | Runtime Evironment library

I am trying to make a library management system in C. I am checking for duplicate ISBN No so that user cannot add two books with same ISBN No. This code was working was last night. It was correctly checking for duplicate ISBN No in the file. But now I checked this morning and it's not working. I cannot understand what is the problem with this code. Everything looks fine to me

I've looked at this thread: Regex to find all sentences of text? but can't seem to get it to solve my exact scenario. Here's the text I'm working with:

I have some code that tranposes my list of dataframes from horizontal format to vertical format. When I inspect the list, I notice that the row numbers of the dataframe are included (664, 665, 670, etc.). To transpose the list, I use lapply(t) which works except that those pesky row numbers are included and now make the resulting list entries not a data frame. I am new to using lapply; Is there a way to use lapply to transpose my list while also excluding those numbers?

Im making a server client system in C using sockets, in my main program of the server, I create multiple threads to have multiple access to the server. I have a file where I store some informantion from the users, when the client disconects from the server, and before closing the thread I want to update the information on the file about that user, using a simple code of copying the file to a temporary file, deleting the main file and renaming the temporary file to the main file name. And I exit my thread.

Issue: The program is not able to delete the main file. But I tested it on the temporary file and it deletes.

I tested multiple things and Im not able to remove the main file, it is allways saying it is unable to delete it.

I unmarshaled CDA(medical standart international document) xml document and I need get value from element family - @XmlElementRef(name = "family", namespace = "urn:hl7-org:v3", type = JAXBElement.class, required = false). I tried to get the value as follows - String firstName = clinicalDocument.getAuthor().get(5).getAssignedAuthor().getAssignedPerson().getName().get(1); Structure of Classes is next.