How to read the last character in a string - c++

Question

I was trying to print the last character of a string, for example str[]="This is an example", I tried to print the 'e' of "example" with some functions, but none of them funct as I expected. I know it's more simple to write in the code the position number of the last character, but as in strrchr function, the code work by itself. Is there a function that works similar?
#include <stdio.h>
#include <string.h>
#include <iostream>
using namespace std;
int main ()
{
char str[] = "This is an example";
char * pch;
pch=strrchr(str,'s');
cout<<str<<endl;
cout<<"Last time 's' was found was in position: "<<pch-str+1<<endl;
cout<<"Last character in this example is "<<str[X];
return 0;
}

Answer 1

From the documentation for strrchr:
The terminating null-character is considered part of the C string. Therefore, it can also be located to retrieve a pointer to the end of a string.
Thus, strrchr(str, '\0')[-1] will have the last character. Note that this is only safe if you're sure str isn't empty.

Answer 2

Simple: use the standard strlen function, as follows:
int main ()
{
char str[] = "This is an example";
char * pch;
pch=strrchr(str,'s');
cout<<str<<endl;
cout<<"Last time 's' was found was in position: "<<pch-str+1<<endl;
size_t X = strlen(str) - 1; // X will be the index of the last character!
cout<<"Last character in this example is "<<str[X];
return 0;
}
Or, just for fun, if you want to handle the case where the string could be empty:
size_t X = strlen(str); X -= !!X; // Non-zero: decrement, Zero: Leave as is
cout<<"Last character in this example is "<<str[X];
Then, for an empty string, cout << str[X] will show whatever the implementation does for a NULL character.

Answer 3

If you don't mind to use std::string this snippet would do the job.
#include <string>
#include <iostream>
int main() {
std::string str = "This is some text";
std::cout << str.back() << std::endl;
}

Answer 4

I assume you choose char[] to avoid allocation or something similar so am not going to discuss std::string as an option.
Three solutions, one in modern C++ using string_view, one using templates ;
and one using std::size and the index operator.
Solution 1.1:
I recommend you use this, its nearly optimal and is much more readable than the alternative. It also doesn't require as much boiler plate to handle empty strings, or strings without null termination.
#include <string_view>
#include <iostream>
int main()
{
std::string_view str = "This is an example";
auto X = str.find_last_of('s');
//
// Make sure the character exists in the string
if (X != std::string_view::npos)
{
std::cout<< str << std::endl;
std::cout<< "Last time 's' was found was in position: " << X << std::endl;
}
else
{
std::cout<<"Character did not exist in string.\n";
}
if (!str.empty()) std::cout<< "Last character in this example is " << str.back();
else std::cout << "Cannot get the last character in an empty string!";
return 0;
}
You can run the solution here:
https://onlinegdb.com/SJK2hjPEB
The same code will work with std::string.
Solution 1.2
This is a compile time only solution, it relies on the string being aggregate constructed or constructed as a string.
template <size_t N>
constexpr char LastCharacter(char (&input)[N])
{
static_assert(N >= 1, "A character array representing a string must have atleast 1 character AND a null terminator.");
return (input[N - 1] == '\0') ? input[N - 2] : input[N - 1];
}
Tests and examples shown here:
https://onlinegdb.com/HJ_IXEd4H
Solution 2
This has the required checks to avoid issues with empty strings.
In this version it is a compile time error to have an empty array. str[] = "" is not an empty array it has 1 character, a null. An empty string has no last character, this needs to be handled. It also should be handled for the strrchr.
If you must use strrchr(...) then consider checking whether the result is nullptr. If a nullptr is returned then the character wasn't found in the string:
#include <stdio.h>
#include <string.h>
#include <iostream>
#include <cassert>
using namespace std;
int main ()
{
char str[] = {'h', 'e','l', 'l', 'o', '\0'};
//
// Prevent use with an empty array (1 character + 1 null character minimum)
if (std::size(str) > 1)
{
//
// Only allow null terminated strings.
assert( str[std::size(str) - 1] == '\0' );
//
// There skip the last null character and get the last character
// No null character, not compensation needed
cout<<"Last character in this example is "<< str[ std::size(str) - 2 ];
}
else
{
cout << "Cannot process empty string\n";
}
return 0;
}
https://onlinegdb.com/SkrP2Q_NB
Please note, defining strings as arrays enables strings to exist without null terminators. In that case the above solution does not function. If you want to handle that case you need to check for the existance of a null terminator and if it is present compensate in code. assert causes an error if there isn't a null terminator.
--
To elaborate on the problem with strrchr. The function requires a null terminated string.
The terminating null-character is considered part of the C string.
Therefore, it can also be located to retrieve a pointer to the end of
a string.
http://www.cplusplus.com/reference/cstring/strrchr/
This was quoted by the previous answer, but for completeness also here.
The datatype you are using allows a character array with no null termination:
char data[] = {'a', 'b', 'c'};
That is what the assert handles in the solution 2.