Is std::container::size_type guaranteed to be size_t for standard containers with default allocator?

Question

Like:

• std::string<T>::size_type
• std::list<T>::size_type
• std::map<T>::size_type
• std::vector<T>::size_type
• etc.

Both cplusplus.com and cppreference.com say that they are usually size_t, but are they truly, unambiguously guaranteed by the standard to be size_t unless a custom allocator is used?

Answer 1

For STL-containers - nope. Table 96 of the standard in [container.requirements.general], which lists container requirements for any container X, explains it pretty clear:

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However, for basic_string, size_type is defined as

typedef typename allocator_traits<Allocator>::size_type size_type;

which in turn will be size_t for std::allocator<..> as the allocator.

Also, std::array uses size_t as size_type, according to [array.overview]/3.