Why can multiple std vectors be used in a class?

Question

From this answer, I am led to believe that the members of a class are guaranteed to be contiguous in memory, in the order that they are declared. However, from the docs, "vectors use contiguous storage locations for their elements". So then how is it possible to have multiple vectors in a class, or a vector that is not the last member of a class, given that a vector may resize and spill over into memory that is already allocated?

Relevant question: [How is vector implemented in C++](https://stackoverflow.com/q/3064559/580083). — Daniel Langr, Jan 07 '20 at 06:34

score 6 · Accepted Answer · answered Jan 07 '20 at 06:30

std::vector is usually implemented as three pointers. One pointer to a dynamically allocated array that stores the vector's contents, one pointer to the end of the used memory and one pointer to the end of the allocated array. No matter how the vector is allocated, the vector's data is stored elsewhere in dynamic storage.

score 1 · Answer 2 · answered Jan 07 '20 at 06:30

1

The memory used by each vector is dynamically allocated.

answered Jan 07 '20 at 06:30

Jesper Juhl

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Why can multiple std vectors be used in a class?

2 Answers2