C Style String in C++

In C, a string is a character array terminated by a null character \0, making its size one more than the number of characters. C++ also supports this, and the compiler automatically adds \0 when initializing the array.

Initializing a String in C++:

1. char str[] = "Geeks";
2. char str[6] = "Geeks";
3. char str[] = {'G', 'e', 'e', 'k', 's', '\0'};
4. char str[6] = {'G', 'e', 'e', 'k', 's', '\0'};

Memory representation of a string "Geeks" in C++.

Commonly Used Functions for C-Style Strings

C-style strings rely on a number of functions defined in the <cstring> header. Let's explore three common functions:

1. strlen (String Length)

The strlen function calculates the length of a string by counting characters until it encounters \0.

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

int main() {
    char s1[] = "gfg";
    char s2[] = {'C', 'P', 'P', '\0'};

    cout << strlen(s1) << endl; 
    cout << strlen(s2) << endl; 
    return 0;
}

3
3

Explanation:

• strlen ignores the null character while calculating the length.
• If the null terminator is missing, strlen may traverse unintended memory, causing incorrect results or runtime errors.

2. strcmp (String Comparison)

The strcmp function compares two strings lexicographically:

• Returns 0 if both strings are equal.
• Returns a negative value if the first string is smaller.
• Returns a positive value if the first string is greater.

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

int main() {
    char s1[] = "gfg";
    char s2[] = "abcd";

    int result = strcmp(s1, s2);

    if (result == 0) {
        cout << "Same" << endl;
    } else if (result < 0) {
        cout << "Smaller" << endl;
    } else {
        cout << "Greater" << endl; 
    }

    return 0;
}

Greater

Explanation:

• Characters are compared one by one based on their ASCII values.
• Comparison stops as soon as a mismatch is found, or one string ends.

3. strcpy (String Copy)

The strcpy function copies the content of one string into another.

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

int main() {
    char str[5];
    strcpy(str, "gfg");

    cout << str << endl; 

    return 0;
}

gfg

Explanation:

• strcpy copies characters, including the null terminator, from the source to the destination.
• Ensure the destination array has enough space to hold the source string and the null terminator.