How Can I Reduce the Capacity of a C std::vector?

Shrinking the Capacity of a std::vector in C

When working with vectors in C , it's often necessary to insert an unknown number of values at runtime. However, once these values are inserted, the vector may retain excess capacity. Reducing this capacity can improve memory efficiency and performance.

To reduce the capacity of a vector, C 11 introduces the shrink_to_fit() member function. As the draft standard section 23.2.6.2 explains, this method:

  is a non-binding request
  to reduce capacity() to size(). <em>[Note: The request is non-binding to
  allow latitude for
  implementation-specific optimizations.
  —end note]</em>

Therefore, it provides a way to make a non-binding request to the compiler to reduce the vector's capacity to match its current size, potentially freeing up unused memory and improving efficiency.

While the extra copy operation could be avoided by manually resizing the vector, shrink_to_fit() offers a more elegant and efficient solution. It's worth noting that this method is non-portable outside of C 11 implementations, but the lack of portability is not a concern for those using GCC, which supports C 11 features.

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