How to get length of a string using strlen function

Question

I have following code that gets and prints a string.

#include<iostream> #include<conio.h> #include<string> using namespace std;  int main() {     string str;     cout << "Enter a string: ";     getline(cin, str);     cout << str;     getch();     return 0; } 

But how to count the number of characters in this string using strlen() function?

Answer 1

For C++ strings, there's no reason to use strlen. Just use string::length:

std::cout << str.length() << std::endl; 

You should strongly prefer this to strlen(str.c_str()) for the following reasons:

1. Clarity: The length() (or size()) member functions unambiguously give back the length of the string. While it's possible to figure out what strlen(str.c_str()) does, it forces the reader to pause for a bit.

2. Efficiency: length() and size() run in time O(1), while strlen(str.c_str()) will take Θ(n) time to find the end of the string.

3. Style: It's good to prefer the C++ versions of functions to the C versions unless there's a specific reason to do so otherwise. This is why, for example, it's usually considered better to use std::sort over qsort or std::lower_bound over bsearch, unless some other factors come into play that would affect performance.

The only reason I could think of where strlen would be useful is if you had a C++-style string that had embedded null characters and you wanted to determine how many characters appeared before the first of them. (That's one way in which strlen differs from string::length; the former stops at a null terminator, and the latter counts all the characters in the string). But if that's the case, just use string::find:

size_t index = str.find(0); if (index == str::npos) index = str.length(); std::cout << index << std::endl; 

Hope this helps!