How to Find Length of a String in C++

1. Use the length Function to Find Length of a String in C++
2. Use the size Function to Find Length of a String in C++
3. Use the while Loop to Find Length of a String in C++
4. Use the std::strlen Function to Find Length of a String in C++

This article will explain several methods of how to find the length of a string in C++.

Use the length Function to Find Length of a String in C++

The C++ standard library provides the std::basic_string class to augment char-like sequences and implement a generic structure for storing and manipulating such data. Although, most people are more familiar with std::string type which is itself type alias for std::basic_string<char>. std::string provides length built-in function to retrieve the length of the stored char sequence.

#include <cstring>
#include <iostream>

using std::cin;
using std::cout;
using std::endl;
using std::string;

int main(int argc, char *argv[]) {
  string str1 = "this is random string oiwaoj";

  cout << "string: " << str1 << endl;
  cout << "length: " << str1.length() << endl;

  exit(EXIT_SUCCESS);
}

Output:

string: this is random string oiwaoj
length: 28

Use the size Function to Find Length of a String in C++

Another built-in function included in the std::string class is size, which behaves similarly to the previous method. It takes no arguments and returns the number of char elements in the string object.

#include <cstring>
#include <iostream>

using std::cin;
using std::cout;
using std::endl;
using std::string;

int main(int argc, char *argv[]) {
  string str1 = "this is random string oiwaoj";

  cout << "string: " << str1 << endl;
  cout << "length: " << str1.size() << endl;

  exit(EXIT_SUCCESS);
}

Output:

string: this is random string oiwaoj
length: 28

Use the while Loop to Find Length of a String in C++

Alternatively, one can implement his/her own function to calculate the length of the string. In this case, we utilize the while loop to traverse the string as a char sequence and increment the counter by one each iteration. Notice that the function takes char* as an argument, and the c_str method is called to retrieve this pointer in the main function. The loop stops when the dereferenced pointer value is equal to 0, and the null-terminated string implementation guarantees that.

#include <cstring>
#include <iostream>

using std::cin;
using std::cout;
using std::endl;
using std::string;

size_t lengthOfString(const char *s) {
  size_t size = 0;

  while (*s) {
    size += 1;
    s += 1;
  }

  return size;
}

int main(int argc, char *argv[]) {
  string str1 = "this is random string oiwaoj";

  cout << "string: " << str1 << endl;
  cout << "length: " << lengthOfString(str1.c_str()) << endl;

  exit(EXIT_SUCCESS);
}

Output:

string: this is random string oiwaoj
length: 28

Use the std::strlen Function to Find Length of a String in C++

Finally, one can resort to the old-school C string library function strlen, which takes a single const char* argument as our custom-defined function - lengthOfString. These last two methods can be faulty when called on char sequences that don’t end with a null byte, as it could access out-of-range memory during the traversal.

#include <cstring>
#include <iostream>

using std::cin;
using std::cout;
using std::endl;
using std::string;

int main(int argc, char *argv[]) {
  string str1 = "this is random string oiwaoj";

  cout << "string: " << str1 << endl;
  cout << "length: " << std::strlen(str1.c_str()) << endl;

  exit(EXIT_SUCCESS);
}

Output:

string: this is random string oiwaoj
length: 28