strlen() in C++

Working with strlen()

Let's look at a simple example of how strlen() works:

#include <iostream>
#include <cstring>


int main() {
    char str[] = "Hello, World!";
    std::cout << "The length of the string is: " << strlen(str);
    return 0;
}

In this code, strlen() calculates the length of the string "Hello, World!" (excluding the null character), and the output will be 13.

Output

Example of strlen() in C++

• C++

C++

#include <iostream>
#include <cstring>

int main() {
    char str[] = "Hello, World!";
    int length = strlen(str);
    std::cout << "Length of the string: " << length << std::endl;
    return 0;
}

You can also try this code with Online C++ Compiler

Run Code

Output

Length of the string: 13

This example demonstrates the usage of the strlen() function to determine the length of a null-terminated string in C++.

strlen() Prototype

The prototype of strlen() function in C++ is:

size_t strlen(const char* str);

Here, str is a pointer to a null-terminated string whose length is to be determined. The function returns a value of type size_t, representing the number of characters in the string, excluding the null character ('\0').

strlen() Undefined Behavior

If the str argument passed to strlen() is not a null-terminated string or if it points to memory that is not accessible, the behavior of the function is undefined. This can lead to unpredictable results, including crashes or incorrect length calculations. It's essential to ensure that the input string is properly null-terminated and valid.

A Closer Look at strlen()

It's crucial to note that strlen() doesn't count the null character that marks the end of the string. If you have a string "Hello" (5 characters) in C++, the null character is automatically appended at the end, making the actual array size 6. But strlen() would return 5.

Another important aspect is that strlen() computes the string length at runtime, not at compile time. This means that if the string content changes, strlen() will return the updated length.

Potential Pitfalls

While strlen() is quite useful, it doesn't perform any array bounds checking. If the given string doesn't contain a null character, strlen() will keep counting until it finds one, possibly leading to buffer overflows. 

Also read -  File Handling in CPP

More Examples of strlen() in C++

1. Program to show the mechanism of the strlen() function

• C++

C++

#include <iostream>
#include <cstring>

int main() {
    char str[] = "We are ninjas and we write code";
    int length = strlen(str);
    std::cout << "Length of the string: " << length << std::endl;
    return 0;
}

You can also try this code with Online C++ Compiler

Run Code

Output

Length of the string: 31

In this example, the strlen() function is used to determine the length of the string "We are ninjas and we write code". The result is then printed to the console.

2. Program to check if the length of two strings is equal or not using the strlen() function

• C++

C++

#include <iostream>
#include <cstring>

int main() {
    char str1[] = "Hello";
    char str2[] = "World";
    
    if (strlen(str1) == strlen(str2)) {
        std::cout << "Length of both strings is equal." << std::endl;
    } else {
        std::cout << "Length of both strings is not equal." << std::endl;
    }
    
    return 0;
}

You can also try this code with Online C++ Compiler

Run Code

Output

Length of both strings is equal.

In this example, the strlen() function is used to determine the lengths of two strings str1 and str2. The lengths are then compared, and a message indicating whether they are equal or not is printed to the console.

Frequently Asked Questions

What does the strlen() function do in C++?

The strlen() function calculates the length of a string, excluding the null character.

Does strlen() count the null character?

No, strlen() doesn't count the null character. It counts only the characters before the null character.

Does strlen() check the array bounds?

No, strlen() doesn't check array bounds, which could lead to buffer overflows if the string doesn't contain a null character.

Conclusion

Understanding the strlen() function is crucial when dealing with strings in C++. It allows you to calculate the string length at runtime. However, remember to always ensure your string contains a null character to avoid potential buffer overflows. 

Recommended articles:

• C++ vs Java
• Virtual Functions & Runtime Polymorphism in C++
• Message Passing in C++
• Difference between Method and Function 
• C++ Interview Questions
• abs in C++