How to Reverse a String in C++ (8 Best Methods with Examples & Complexity)
Reversing a string in C++ means rearranging its characters so that the last character becomes first and the first becomes last.
Example:
Input:
Hello
Output:
olleHReversing strings is one of the most common beginner exercises and interview questions in C++. However, there are multiple ways to do it, each with different tradeoffs in performance, memory usage, and portability.
The best way to reverse a string in C++ is:
#include <algorithm>
#include <iostream>
using namespace std;
int main() {
string str = “Hello”;
reverse(str.begin(), str.end());
cout << str;
}
Time Complexity: O(n)
Space Complexity: O(1)
In-place reversal: Yes
This is the most efficient and production-ready solution.
Method 1: Using STL reverse() (Recommended)
The Standard Template Library provides reverse() in <algorithm>.
#include <algorithm>
#include <iostream>
using namespace std;
int main() {
   string str = "Hello";
   reverse(str.begin(), str.end());
   cout << str;
}Why this method is preferred:
- Clean and readable
- Optimized implementation
- No extra memory allocation
- Standard and portable
Method 2: Using Reverse Iterators (Constructor Method)
You can construct a reversed string using reverse iterators.
#include <iostream>
using namespace std;
int main() {
   string str = "Hello";
   string reversed(str.rbegin(), str.rend());
   cout << reversed;
}Time Complexity: O(n)
Space Complexity: O(n)
This creates a new reversed string instead of modifying the original.
Method 3: Manual Loop with Temporary String
#include <iostream>
using namespace std;
int main() {
   string str = "Hello";
   string reversed;
   for(int i = str.length() - 1; i >= 0; i--) {
       reversed.push_back(str[i]);
   }
   cout << reversed;
}Time Complexity: O(n)
Space Complexity: O(n)
Useful for understanding how string traversal works internally.
Method 4: Two Pointer In-Place Swap (Interview Favorite)
#include <iostream>
using namespace std;
int main() {
   string str = "Hello";
   int left = 0;
   int right = str.length() - 1;
   while(left < right) {
       swap(str[left], str[right]);
       left++;
       right--;
   }
   cout << str;
}Time Complexity: O(n)
Space Complexity: O(1)
This is a very common interview solution because it demonstrates algorithmic thinking.
Method 5: Using Recursion
#include <iostream>
using namespace std;
void reverseString(string &str, int start, int end) {
   if(start >= end) return;
   swap(str[start], str[end]);
   reverseString(str, start + 1, end - 1);
}
int main() {
   string str = "Hello";
   reverseString(str, 0, str.length() - 1);
   cout << str;
}Time Complexity: O(n)
Space Complexity: O(n) due to recursion stack
Good for demonstrating recursion but not memory efficient.
Method 6: Reversing a C-Style String (char array)
#include <iostream>
#include <cstring>
using namespace std;
int main() {
   char str[] = "Hello";
   int n = strlen(str);
   for(int i = 0; i < n / 2; i++) {
       swap(str[i], str[n - i - 1]);
   }
   cout << str;
}Important Note:
strrev() is not part of the ISO C++ standard. It may work in some compilers but is not portable. Avoid using it in modern development.
Method 7: Using Stack
#include <iostream>
#include <stack>
using namespace std;
int main() {
   string str = "Hello";
   stack<char> s;
   for(char c : str)
       s.push(c);
   string reversed;
   while(!s.empty()) {
       reversed += s.top();
       s.pop();
   }
   cout << reversed;
}Time Complexity: O(n)
Space Complexity: O(n)
Primarily educational for understanding stack behavior.
Method 8: Using C++20 ranges::reverse
If using C++20:
#include <iostream>
#include <ranges>
using namespace std;
int main() {
   string str = "Hello";
   ranges::reverse(str);
   cout << str;
}Requires C++20 compiler support.
Best for modern C++ applications.
Complexity Comparison Table
| Method | Time | Space | In-Place |
| STL reverse | O(n) | O(1) | Yes |
| Reverse iterators | O(n) | O(n) | No |
| Manual loop | O(n) | O(n) | No |
| Two pointer | O(n) | O(1) | Yes |
| Recursion | O(n) | O(n) | Yes |
| Stack | O(n) | O(n) | No |
| C++20 ranges | O(n) | O(1) | Yes |
Best Overall: STL reverse()
Edge Cases to Consider
- Empty string
- Single character
- String with spaces
- Special characters
- Very large strings
- UTF-8 or multi-byte characters
Important:
Reversing UTF-8 strings byte by byte can corrupt multi-byte characters. For internationalized applications, use proper Unicode libraries instead of simple char reversal.
Common Interview Variations
- Reverse words in a sentence
- Check if string is palindrome
- Reverse only vowels
- Reverse without extra memory
- Reverse linked list of characters
Being able to explain time and space complexity is critical.
Frequently Asked Questions
Q) What is the best way to reverse a string in C++?
A) Using STL reverse() because it is efficient, clean, and standard compliant.
Q) What is the time complexity of reverse() in C++?
A) O(n), where n is the length of the string.
Q) Is strrev() standard in C++?
A) No. It is not part of the ISO C++ standard and should be avoided.
Q) How do you reverse a string without STL?
A) Use the two-pointer swap method.
Q) How to reverse a char array in C++?
A) Use a loop swapping characters from both ends toward the center.
Q) Is recursion a good method for reversing a string?
A) It works but consumes additional stack memory, so it is not optimal for large strings.
Q) Can C++ safely reverse UTF-8 strings?
A) Not by default. You must use Unicode-aware libraries for safe reversal.
Final Conclusion
Reversing a string in C++ is a fundamental operation with multiple valid implementations. While manual loops and recursion help build algorithmic understanding, the STL reverse() function remains the best choice for real-world applications.
If you are preparing for interviews, master:
- Two pointer approach
- STL reverse
- Complexity analysis
If you are writing production code, prioritize:
- Portability
- Standard compliance
- Memory efficiency
With the methods, comparisons, and edge cases covered above, you now have a complete and modern understanding of string reversal in C++ suitable for both interviews and professional development.