Adding data to a sorted file in a sorted way

Question

I have a file (text) where every line is in this form: Name(15 characters) LastName(20 char) Code(4char)
And those names are sorted alphabetically.
I will everytime get a name a last name and a code and try to insert that new data in the correspondant place
For example if the line 3 and 4 are
Jack Thomson 1234
Jordan Mark 5677
And the user enters James Kabelo 2615
I have to put him between jack and jordan.

I m asked to do that using an intermediate file.
Who can help please?

Answer 1

And the function prototype is :
FILE* add_pers(FILE *fp, FILE *fp1)
Thanks. ♡