C, string, array, big file

[Jim Li]

I need to manipulate (searching, sorting, ...) some big files (>500K)
What is the best way to store the contents of the files?
Suppose I have a file that is 5000 lines long, the simplest decl. would be

char array[5000][80]; 

Any better ideas?           
(Speed is a key issue.)

Thanks in advance.
Jim.
.