Case insensitive string comparison C++ [duplicate]

Answer 1

You can write a simple function to convert the existing string to lower case as follows:

#include <string>
#include <ctype.h>
#include <algorithm>
#include <iterator>
#include <iostream>

std::string make_lowercase( const std::string& in )
{
  std::string out;

  std::transform( in.begin(), in.end(), std::back_inserter( out ), ::tolower );
  return out;
}

int main()
{
  if( make_lowercase( "Hello, World!" ) == std::string( "hello, world!" ) ) {
    std::cout << "match found" << std::endl;
  }

  return 0;
}

Answer 2

usually what I do is just compare a lower-cased version of the string in question, like:

if (foo.make_this_lowercase_somehow() == "stack overflow") {
  // be happy
}

I believe boost has built-in lowercase conversions, so:

#include <boost/algorithm/string.hpp>    

if (boost::algorithm::to_lower(str) == "stack overflow") {
  //happy time
}

Answer 3

strncasecmp

The strcasecmp() function performs a byte-by-byte comparison of the strings s1 and s2, ignoring the case of the characters. It returns an integer less than, equal to, or greater than zero if s1 is found, respectively, to be less than, to match, or be greater than s2.

The strncasecmp() function is similar, except that it compares no more than n bytes of s1 and s2...

Answer 4

why don't you you make everything lower case and then compare?

tolower()

  int counter = 0;
  char str[]="HeLlO wOrLd.\n";
  char c;
  while (str[counter]) {
    c = str[counter];
    str[counter] = tolower(c);
    counter++;
  }

  printf("%s\n", str);

Answer 5

I just wrote this, maybe it can be useful to somebody:

int charDiff(char c1, char c2)
{
    if ( tolower(c1) < tolower(c2) ) return -1;
    if ( tolower(c1) == tolower(c2) ) return 0;
    return 1;
}

int stringCompare(const string& str1, const string& str2)
{
    int diff = 0;
    int size = std::min(str1.size(), str2.size());
    for (size_t idx = 0; idx < size && diff == 0; ++idx)
    {
        diff += charDiff(str1[idx], str2[idx]);
    }
    if ( diff != 0 ) return diff;

    if ( str2.length() == str1.length() ) return 0;
    if ( str2.length() > str1.length() ) return 1;
    return -1;
}