Are std::vector Elements Guaranteed to Be Contiguous in Memory?

Can I Treat std::vector Elements as Contiguous Arrays?

The question arises whether the elements within a std::vector are guaranteed to occupy contiguous memory addresses, allowing us to treat its pointer to the first element as a C-array.

Historical Context:

In the C 98 standard, this guarantee was absent. Nevertheless, the standard's requirements for std::vector made it unlikely that elements would be non-contiguous.

Current Standard:

However, this matter was clarified in the C 0x (later renamed to C 11) standard. According to the TR that amended the C 98 standard: "The elements of a vector are stored contiguously." This means that for a vector of type other than bool, the following holds true:

&v[n] == &v[0] + n

where:

• v is the vector
• n is an index between 0 and v.size() - 1

Example:

As a result, the following code is now valid and will function as expected:

std::vector<int> values;
// ... fill up values

if( !values.empty() )
{
    int *array = &values[0];
    for( int i = 0; i < values.size(); ++i )
    {
        int v = array[i];
        // do something with 'v'
    }
}

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