C++ Cookbook

4.14. Doing a Case-Insensitive String Search

Problem

You want to find a substring in a string without regard for case.

Solution

Use the standard algorithms transform and search, defined in <algorithm>, along with your own special character comparison functions, similar to the approach presented in. Example 4-22 shows how to do this.

Example 4-22. Case-insensitive string search

#include <string>
#include <iostream>
#include <algorithm>
#include <iterator>
#include <cctype>

using namespace std;

inline bool caseInsCharCompSingle(char a, char b) {
   return(toupper(a) == b);
}

string::const_iterator caseInsFind(string& s, const string& p) {
   string tmp;

   transform(p.begin(), p.end(),             // Make the pattern
             back_inserter(tmp),                 // upper-case
             toupper);

   return(search(s.begin(), s.end(),         // Return the iter- 
                 tmp.begin(), tmp.end(),     // ator returned by
                 caseInsCharCompSingle));        // search
}

int main() {
   string s = "row, row, row, your boat";
   string p = "YOUR";
   string::const_iterator it = caseInsFind(s, p);

   if (it != s.end()) {
      cout << "Found it!\n";
   }
}

By returning an iterator that refers to the element in the target string where the pattern string starts, you ensure ease of compatibility with other standard algorithms since most of them accept iterator arguments.

Discussion

Example 4-22 demonstrates the usual mode of operation when working with standard algorithms. Create the functions that do the work, then plug them into the most appropriate algorithms as function objects. The charInsCharCompSingle function ...