[c++] How to get length of a string using strlen function

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?

Use std::string::size or std::string::length (both are the same).

As you insist to use strlen, you can:

int size = strlen( str.c_str() );

note the usage of std::string::c_str, which returns const char*.

BUT strlen counts untill it hit \0 char and std::string can store such chars. In other words, strlen could sometimes lie for the size.

Function strlen shows the number of character before \0 and using it for std::string may report wrong length.

strlen(str.c_str()); // It may return wrong length.

In C++, a string can contain \0 within the characters but C-style-zero-terminated strings can not but at the end. If the std::string has a \0 before the last character then strlen reports a length less than the actual length.

Try to use .length() or .size(), I prefer second one since another standard containers have it.

str.size()

Manually:

int strlen(string s)
{
    int len = 0;

    while (s[len])
        len++;

    return len;
}

If you really, really want to use strlen(), then

cout << strlen(str.c_str()) << endl;

else the use of .length() is more in keeping with C++.

Simply use

int len=str.length();

#include<iostream>
#include<conio.h>
#include<string.h>
using namespace std;
int main()

{
    char str[80];

    int i;

    cout<<"\n enter string:";

    cin.getline(str,80);

    int n=strlen(str);

    cout<<"\n lenght is:"<<n;

    getch();

    return 0;

}

This is the program if you want to use strlen . Hope this helps!