Is it safe to assume memory contiguity in STL vectors?

Memory Contiguity in STL Vectors: A Safe Assumption

The issue at hand concerns the storage arrangement of elements within an STL vector. Specifically, the question arises whether it is prudent to assume that the vector's elements are stored contiguously in memory, allowing for the safe retrieval of subsequent elements using the address of the first element.

According to the C 03 standard (23.2.4.1), this assumption indeed holds true:

"The elements of a vector are stored contiguously, meaning that if v is a vector where T is some type other than bool, then it obeys the identity &v[n] == &v[0] n for all 0 <= n < v.size()."

This implies that after resizing a vector, the address of its first element can be safely used to access the remaining elements sequentially. The formula &vc[n] == &vc[0] n provides a reliable mechanism for calculating the memory offsets of subsequent elements.

However, it is crucial to note that this assumption remains valid only until the vector is reallocated. Adding elements to the vector may trigger a reallocation operation, rendering any existing pointers and iterators invalid. Therefore, it is essential to exercise caution when dealing with vectors that are subject to potential reallocation.

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