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strlen() in C++

strlen() in C++

By Pawan Harwani
2 mins read
Last updated: 19 Oct 2023
176 views
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Overview

The strlen() function returns the length of the given string, excluding the null character('\0'). It is defined in the cstring header file in C++.

Introduction

The strlen() function returns the length of the given string, excluding the null character('\0'). It is defined in the cstring header file in C++. The strlen() in c++ shows undefined behaviour when the string passed to it is not null terminated.

Syntax of strlen() in C++

str is the name of the string whose length we need to find, and it is typecast to const char*.

Parameters of strlen() in C++

strlen() in c++ accepts a pointer to the null-terminated string whose length is to be calculated.

Return Value of strlen() in C++

The strlen() in c++ returns the length of the string passed.

Note: The returned length does not include the null character '\0'.

Example of strlen() in C++

This program demonstrates the use of strlen() function.

Output :

strlen() Prototype

The prototype of the strlen() in c++ is defined in cstring header file :

The size_t is used to represent size of variables/objects in bytes.

  • It guarantees to be big enough to contain the size of the biggest object that the system can handle.
  • If a system is 32 bits, then size_t represents unsigned int.
  • If a system is 64 bits, then size_t represents unsigned long long.

Difference between size_t and int is that in case of size_t, it is not defined how large it is, i.e., it can be long int or long long int but int size is fixed.

strlen() Undefined Behavior

The strlen() in c++ shows undefined behaviour when the string passed to it is not null terminated.

Example showing undefined behavior:

Output:

Explanation: As we know that the undefined behavior of strlen() is that, it is meant to be used with char arrays or null terminated strings, so when it is used with a string which is not null-terminated, either it produces an unexpected result or it fails to produce a result.

More Examples of strlen() in C++?

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

Output :

Explanation : This is the usual behaviour of strlen() function in C++, as discussed before, and it will return the length of the string passed.

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

Output:

Explanation : The length of the two strings, a and b are equal, i.e, 4, Therefore, it prints string lengths are equal.

Conclusion

  1. The strlen() function returns the length of the given string excluding the null character('\0').
  2. strlen() function is defined in the cstring header file in C++.
  3. strlen() in C++ shows undefined behavior when the string passed to it is not null terminated, therefore, it is recommended to include null character at the end of the string when declared as character array.