Get the last element of a std:: string

In C++, retrieving the last character of std::string can be achieved in multiple ways. The following are several common methods:

Method 1: Using the Subscript Operator

If the string is non-empty, you can directly access the last character using the subscript operator []:

cpp
std::string str = "Hello, World!";
char lastChar = str[str.length() - 1];

Here, str.length() - 1 provides the index of the last character.

Method 2: Using the at() Member Function

The at() function provides bounds checking. If the index is out of bounds, it throws a std::out_of_range exception. This makes using the at() method safer than using the subscript operator directly:

cpp
std::string str = "Hello, World!";
try {
    char lastChar = str.at(str.length() - 1);
} catch (std::out_of_range& e) {
    std::cerr << "Out of range error: " << e.what() << '\n';
}

Method 3: Using the back() Member Function

Since C++11, std::string provides the back() function, which directly returns the last character of the string. It is convenient and concise:

cpp
std::string str = "Hello, World!";
char lastChar = str.back();  // Directly retrieves the last character

The back() function assumes the string is not empty; calling it on an empty string may result in undefined behavior.

Method 4: Using Iterators

You can also access the last character using iterators, which provides a consistent interface when working with strings and other containers:

cpp
std::string str = "Hello, World!";
if (!str.empty()) {
    auto lastChar = *(str.end() - 1);
}

Here, str.end() returns an iterator pointing to the end of the string (the position after the last character), so subtracting 1 gives the iterator for the last character.

Example Usage

Suppose we need to write a function that prints the last character of a provided std::string (if the string is not empty):

cpp
void printLastCharacter(const std::string& str) {
    if (!str.empty()) {
        char lastChar = str.back();  // Using the back() function to retrieve the last character
        std::cout << "The last character is: " << lastChar << std::endl;
    } else {
        std::cout << "The string is empty." << std::endl;
    }
}

// Example call
int main() {
    std::string testStr = "Hello, World!";
    printLastCharacter(testStr);
    return 0;
}

These methods demonstrate how to safely and efficiently retrieve the last character of std::string in practical applications.