Convert each character of a string to uppercase in C++

This post will discuss how to convert each character of a string to uppercase in C++.

1. Using Boost Library

A simple and efficient solution is to use the boost::algorithm::to_upper to convert each character of std::string to uppercase.

#include <iostream>

#include <boost/algorithm/string.hpp>

using namespace std;

int main()

{

string s = "boost library";

boost::to_upper(s);

cout << s << endl;

return 0;

}

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Output:

BOOST LIBRARY

We can also use boost::algorithm::to_upper_copy, which returns a “copy” of the string object in uppercase.

2. Using `std::for_each` function

If the boost library is not available, try using the standard algorithm std::for_each, which applies a given function object to every character of the string. The function needs to convert a character to uppercase in-place, as shown below:

#include <iostream>

#include <cctype>

#include <algorithm>

using namespace std;

struct convert

{

void operator()(char &ch) {

ch = toupper(static_cast<unsigned char>(ch));

}

};

void to_upper(char &ch) {

ch = toupper(static_cast<unsigned char>(ch));

}

int main()

{

// 1. for_each + unary function

string s = "function";

for_each(s.begin(), s.end(), to_upper);

cout << s << endl;

// 2. for_each + object of a class implementing ()operator

s = "class object";

for_each(s.begin(), s.end(), convert());

cout << s << endl;

// 3. for_each + lambda expression (C++11)

s = "lambdas";

for_each(s.begin(),

s.end(),

[](char &ch) {

ch = ::toupper(static_cast<unsigned char>(ch));

});

cout << s << endl;

return 0;

}

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Output:

FUNCTION
CLASS OBJECT
LAMBDAS

3. Using `std::transform` function

Another good alternative is to use the STL algorithm std::transform, which applies a function to the specified range and stores the result in another range, which begins at the specified output iterator.

#include <iostream>

#include <algorithm>

#include <cctype>

using namespace std;

struct convert

{

unsigned char operator()(unsigned char const &ch) {

return toupper(ch);

}

};

int main()

{

// 1. for_each + unary function

string s = "function";

transform(s.begin(), s.end(), s.begin(), ::toupper);

cout << s << endl;

// 2. for_each + object of a class implementing ()operator

s = "class object";

transform(s.begin(), s.end(), s.begin(), convert());

cout << s << endl;

// 3. for_each + lambda expression (C++11)

s = "lambdas";

transform(s.begin(),

s.end(),

s.begin(),

[](unsigned char const &ch) {

return ::toupper(ch);

});

cout << s << endl;

return 0;

}

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Output:

FUNCTION
CLASS OBJECT
LAMBDAS

4. Naive solution

Finally, we can write our own function for converting characters of a string to uppercase. This is demonstrated below:

#include <iostream>

#include <cctype>

using namespace std;

char to_upper(char ch)

{

if (ch >= 'a' && ch <= 'z') {

return ch - 32;

}

return ch;

}

int main()

{

string s = "naive solution";

for (char &ch: s) {

ch = to_upper(ch);

}

cout << s;

return 0;

}

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Output:

NAIVE SOLUTION

That’s all about converting each character of a string to uppercase in C++.

Convert each character of a string to uppercase in C++

1. Using Boost Library

2. Using std::for_each function

3. Using std::transform function

4. Naive solution

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2. Using `std::for_each` function

3. Using `std::transform` function