Convert First Letter of each word of a String to Upper Case in C++

In this article we will discuss different ways to convert first letter of each word to upper case in a a given string i.e.

• Using STL algorithm
• Using Boost Filtered Iterator & Range

Converting First Letter to Upper Case using STL

Algorithm Used:

• Iterate over the characters in given string
• For each character check – if last char was ‘ ‘ and current is not ‘ ‘
• If yes the convert that letter to upper case

Complete code is as follows,

#include <iostream>
#include <string>
#include <algorithm>

int main() {
	std::string data = "hi this is a sample string.";

	// Iterate over all the characters in a string
	// and call a lambda function on each of them
	std::for_each(data.begin(), data.end(), [](char & c) {
					static int last = ' ';
					if(last == ' ' && c != ' ' && ::isalpha(c))
					c = ::toupper(c);
					last = c;
				});

	std::cout << data << std::endl;
}

Output:

Hi This Is A Sample String.

 

Converting First Letter to Upper Case using Boost Library

Boost Library provides a function to convert a input sequence to upper case i.e.

template<typename WritableRangeT>
void to_upper(WritableRangeT & Input, const std::locale & Loc = std::locale());

Here input sequenece can be a string or a range of iterators i.e. boost::iterator_range

But here we don’t want to convert whole string to upper case. We want few specific characters to be converted to upper case only. Therefore we will create a Range of Filtered Iterator.

Filtered Iterator

Filtered Iterator is an adaptor iterator that will skip certain elements based based on filter i.e. an attached callback.

Let’s first create a callback that will accept a char and return true if last character received was whitespace ‘ ‘ and current char is an alphabet.

struct IsFirstLetter
{
	// Return true if last char was ' ' & current char is an alphabet.
	bool operator()(char & c) {
		static int last = ' ';
		if (last == ' ' && c != ' ' && ::isalpha(c)) {
			last = c;
			return true;
		}
		last = c;
		return false;
	}
};

Now let’s create Start and End Filtered String Iterator that will iterate through only those characters which when passed to above filter callback returns true i.e.

std::string data = "hi this is a sample string.";

typedef boost::filter_iterator<IsFirstLetter, std::string::iterator> FilterIter;

// Creating Filter i.e. a Functor Object
IsFirstLetter isFirstLetterObj;

// Create start of Filtered Iterator
FilterIter filter_iter_first(isFirstLetterObj, data.begin(), data.end());
// Create End of Filtered Iterator
FilterIter filter_iter_last(isFirstLetterObj, data.end(), data.end());

Now create a Range from this start and end filtered iterator i.e.

// Create a Range from start & end filetered iterator object
boost::iterator_range<FilterIter> strRange;
strRange = boost::make_iterator_range(filter_iter_first, filter_iter_last);

Now use this range with boost::to_upper to convert only those characters to uppercase which are in filtered iterator i.e.

// convert string to upper case
boost::to_upper(strRange);

Complete example is as follows,

#include <iostream>
#include <string>
#include <algorithm>
#include <boost/algorithm/string.hpp>
#include <boost/iterator/filter_iterator.hpp>

struct IsFirstLetter {
	// Return true if last char was ' ' & current char is an alphabet.
	bool operator()(char & c) {
		static int last = ' ';
		if (last == ' ' && c != ' ' && ::isalpha(c)) {
			last = c;
			return true;
		}
		last = c;
		return false;
	}
};

int main() {
	std::string data = "hi this is a sample string.";

	typedef boost::filter_iterator<IsFirstLetter, std::string::iterator> FilterIter;

	// Creating Filter i.e. a Functor Object
	IsFirstLetter isFirstLetterObj;

	// Create start of Filtered Iterator
	FilterIter filter_iter_first(isFirstLetterObj, data.begin(), data.end());
	// Create End of Filtered Iterator
	FilterIter filter_iter_last(isFirstLetterObj, data.end(), data.end());

	// Create a Range from start & end filetered iterator object
	boost::iterator_range<FilterIter> strRange;
	strRange = boost::make_iterator_range(filter_iter_first, filter_iter_last);

	// convert string to upper case
	boost::to_upper(strRange);

	std::cout << data << std::endl;
}

Output:

Hi This Is A Sample String.