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Difference between revisions of "cpp/container/inplace vector/try emplace back"

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m (→‎Example: +)
 
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{{example
 
{{example
 
|code=
 
|code=
 +
#include <cassert>
 +
#include <complex>
 +
#include <inplace_vector>
 +
 +
int main()
 +
{
 +
    using namespace std::complex_literals;
 +
    using C = std::complex<double>;
 +
    using I = std::inplace_vector<C, 3>;
 +
    auto v = I{1.0 + 2.0i, 3.0 + 4.0i};
 +
 +
    C* c = v.try_emplace_back(5.0, 6.0);
 +
    assert(*c == 5.0 + 6.0i);
 +
    assert((v == I{1.0 + 2.0i, 3.0 + 4.0i, 5.0 + 6.0i}));
 +
 +
    c = v.try_emplace_back(7.0, 8.0); // no space => no insertion
 +
    assert(c == nullptr);
 +
    assert((v == I{1.0 + 2.0i, 3.0 + 4.0i, 5.0 + 6.0i}));
 +
}
 
}}
 
}}
  

Latest revision as of 03:11, 27 August 2024

 
C++
 
Containers library
 
std::inplace_vector
Member types
Member functions
Non-member functions
 
template< class... Args >
constexpr pointer try_emplace_back( Args&&... args );
 (since C++26)

Conditionally appends an object of type T to the end of the container.

If size() == capacity() is true, there are no effects. Otherwise, appends direct-non-list-initialized with std::forward<Args>(args)... object of type T.

No iterators or references are invalidated, except end(), which is invalidated if the insertion occurs.

Contents

[edit] Parameters

args - arguments to forward to the constructor of the element
Type requirements
-
T must be EmplaceConstructible into inplace_vector from std::forward<Args>(args)....

[edit] Return value

std::addressof(back()) if size() < capacity(), nullptr otherwise.

[edit] Complexity

Constant.

[edit] Exceptions

Any exception thrown by initialization of inserted element. If an exception is thrown for any reason, this function has no effect (strong exception safety guarantee).

[edit] Notes

This section is incomplete
Reason: Explain the purpose of this API.

[edit] Example

Run this code
#include <cassert>
#include <complex>
#include <inplace_vector>
 
int main()
{
    using namespace std::complex_literals;
    using C = std::complex<double>;
    using I = std::inplace_vector<C, 3>;
    auto v = I{1.0 + 2.0i, 3.0 + 4.0i};
 
    C* c = v.try_emplace_back(5.0, 6.0);
    assert(*c == 5.0 + 6.0i);
    assert((v == I{1.0 + 2.0i, 3.0 + 4.0i, 5.0 + 6.0i}));
 
    c = v.try_emplace_back(7.0, 8.0); // no space => no insertion
    assert(c == nullptr);
    assert((v == I{1.0 + 2.0i, 3.0 + 4.0i, 5.0 + 6.0i}));
}

[edit] See also

 constructs an element in-place at the end
(public member function) [edit]
adds an element to the end
(public member function) [edit]
adds a range of elements to the end
(public member function) [edit]
tries to add a range of elements to the end
(public member function) [edit]
unconditionally constructs an element in-place at the end
(public member function) [edit]
unconditionally adds an element to the end
(public member function) [edit]
removes the last element
(public member function) [edit]
creates a std::back_insert_iterator of type inferred from the argument
(function template) [edit]
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