.capacity()

In C++, the .capacity() method returns the amount of storage currently allocated for the string. This capacity is always equal to or greater than the value returned by the .size() method. The .capacity() method is useful for optimizing performance in scenarios where a string undergoes frequent modifications. It helps determine how much memory is already allocated, which can reduce unnecessary reallocations during operations such as appending in loops or constructing large strings. When used alongside .reserve(), it enables preallocation of sufficient space, enhancing efficiency in performance-critical applications.

Syntax

string.capacity();

Parameters:

• The .capacity() method does not take any parameters.

Return value:

Returns a size_t value representing the number of characters the string can hold without requiring a reallocation of memory.

Example

This example demonstrates the basic usage of the .capacity() method and how it can differ from the .size() of the string:

#include <iostream>
#include <string>

using namespace std;

int main() {
  string message = "Hello";

  cout << "String: " << message << '\n';
  cout << "Size: " << message.size() << '\n';
  cout << "Capacity: " << message.capacity() << '\n';

  return 0;
}

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The output of the code above will be:

String: Hello
Size: 5
Capacity: 15

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Codebyte Example

This codebyte example shows how the .capacity() of a string can grow when needed, and how it may stay the same when there’s already enough reserved space:

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