String Handling in C++: C-Style and std::string

In C++, text (string) operations can be performed using both traditional C-style character arrays (char arrays) and the modern std::string class. C-style arrays provide low-level control, while the std::string class is safer and more convenient. In this article, we’ll explore all aspects of working with strings in detail.

1. C-Style Strings (char arrays)

C-style strings are char arrays terminated by a null character ('\0'). They are stored in memory as a contiguous sequence of characters.

#include <iostream>
using namespace std;

int main() {
    char message1[] = "Hello";       // '\0' is added automatically
    char message2[20] = "C++";       // Maximum 19 characters + '\0'

    cout << message1 << " " << message2 << endl;
    return 0;
}

When working with C-style strings, it is crucial to avoid exceeding the array’s boundary. C++ does not automatically check array limits for C-style strings.

2. strcpy, strcat, strlen, strcmp (C String Functions)

When using C-style strings, the functions from the <cstring> library are commonly used:

#include <iostream>
#include <cstring>
using namespace std;

int main() {
    char a[20] = "C++";
    char b[20] = "Programming";

    // Concatenation
    strcat(a, " ");        // a = "C++ "
    strcat(a, b);          // a = "C++ Programming"

    // Copy
    char c[20];
    strcpy(c, a);

    // Length
    cout << "Length: " << strlen(a) << endl;

    // Comparison
    if (strcmp(a, c) == 0)
        cout << "A and C are equal." << endl;

    cout << "Result: " << a << endl;
}

These functions must be used carefully, as they can cause buffer overflows. In modern C++, it is recommended to use std::string instead.

3. Introduction to the std::string Class

In modern C++, the <string> library is used for text manipulation. std::string objects can grow dynamically, handle memory management automatically, and provide rich functionality.

#include <iostream>
#include <string>
using namespace std;

int main() {
    string firstName = "Ali";
    string lastName = "Yilmaz";
    string fullName = firstName + " " + lastName;

    cout << "Hello " << fullName << endl;
    return 0;
}

The std::string type can easily be concatenated using the + operator and compared directly using ==.

4. Basic String Operations

string text = "Programming";
cout << text.length() << endl;   // 11
cout << text.substr(0, 7) << endl; // "Program"

5. Searching, Replacing, and Erasing

std::string provides many powerful text manipulation methods:

string message = "C++ programming language";

// Search
size_t position = message.find("programming");
if (position != string::npos)
    cout << "'programming' found at index: " << position << endl;

// Replace
message.replace(4, 11, "modern"); // replace 11 characters starting from index 4
cout << message << endl; // "C++ modern language"

// Erase
message.erase(4, 7); // delete 7 characters starting from index 4
cout << message << endl; // "C++ language"

The find() method returns string::npos if the substring is not found. This value indicates “not found”.

6. Character-Level Operations

Since a string consists of characters, it can be processed character by character using loops.

#include <iostream>
#include <string>
using namespace std;

int main() {
    string word = "Cplusplus";

    for (char c : word) {
        cout << c << " ";
    }

    cout << endl;

    // Convert to uppercase
    for (char &c : word) {
        c = toupper(c);
    }
    cout << word << endl;
}

For character conversions, use <cctype> functions such as toupper() and tolower().

7. Conversion Operations (string <→ int, double)

A std::string can be converted to numeric values and vice versa.

#include <iostream>
#include <string>
using namespace std;

int main() {
    string numberText = "42";
    int number = stoi(numberText); // string → int
    double d = stod("3.14");       // string → double

    cout << number + 10 << endl; // 52
    cout << d * 2 << endl;       // 6.28

    // int → string
    int age = 25;
    string text = to_string(age);
    cout << "Age: " << text << endl;
}

8. Comparison (compare, ==, <, >)

Strings can be compared using either the compare() method or comparison operators.

string a = "Ali";
string b = "Veli";

if (a == b)
    cout << "Equal" << endl;
else if (a < b)
    cout << "A comes before alphabetically" << endl;
else
    cout << "A comes after alphabetically" << endl;

9. Input and Output Operations

The cin object only reads input until the first whitespace character. If you want to read an entire sentence, use the getline() function.

#include <iostream>
#include <string>
using namespace std;

int main() {
    string name;
    cout << "Enter your name: ";
    cin >> name;
    cout << "Hello, " << name << endl;

    cin.ignore(); // clear the newline character left in the buffer

    string sentence;
    cout << "Enter a sentence: ";
    getline(cin, sentence);

    cout << "You entered: " << sentence << endl;
}

The getline() function reads the entire line, including spaces.

10. Example Application: Text Analysis

The following example counts the number of words and letters in a user-provided sentence.

#include <iostream>
#include <string>
#include <cctype>
using namespace std;

int main() {
    string text;
    cout << "Enter a sentence: ";
    getline(cin, text);

    int charCount = 0;
    int wordCount = 1;

    for (char c : text) {
        if (isalpha(c))
            charCount++;
        if (c == ' ')
            wordCount++;
    }

    cout << "Character count: " << charCount << endl;
    cout << "Word count: " << wordCount << endl;
    return 0;
}

11. TL;DR

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