12.3. Using the Library: A Text-Query Program

To conclude our discussion of the library, we’ll implement a simple text-query program. Our program will let a user search a given file for words that might occur in it. The result of a query will be the number of times the word occurs and a list of lines on which that word appears. If a word occurs more than once on the same line, we’ll display that line only once. Lines will be displayed in ascending order—that is, line 7 should be displayed before line 9, and so on.

For example, we might read the file that contains the input for this chapter and look for the word element. The first few lines of the output would be

element occurs 112 times
   (line 36) A set element contains only a key;
   (line 158) operator creates a new element
   (line 160) Regardless of whether the element
   (line 168) When we fetch an element from a map, we
   (line 214) If the element is not found, find returns

followed by the remaining 100 or so lines in which the word element occurs.