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std::multimap<Key,T,Compare,Allocator>::begin, std::multimap<Key,T,Compare,Allocator>::cbegin - cppreference.com

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iterator begin();

 (1) (noexcept since C++11)

const_iterator begin() const;

 (2) (noexcept since C++11)

const_iterator cbegin() const noexcept;

 (3) (since C++11)

Returns an iterator to the first element of the multimap.

If the multimap is empty, the returned iterator will be equal to end().

Return value

Iterator to the first element.

Complexity

Constant.

Notes

libc++ backports cbegin() to C++98 mode.

Example

#include <algorithm>
#include <cassert>
#include <cstddef>
#include <iostream>
#include <map>
#include <string>

int main()
{
    auto show_node = [](const auto& node, char ending = '\n')
    {
        std::cout << "{ " << node.first << ", " << node.second << " }" << ending;
    };

    std::multimap<std::size_t, std::string> mmap;
    assert(mmap.begin() == mmap.end());   // OK
    assert(mmap.cbegin() == mmap.cend()); // OK

    mmap.insert({ sizeof(long), "LONG" });
    show_node(*(mmap.cbegin()));
    assert(mmap.begin() != mmap.end());   // OK
    assert(mmap.cbegin() != mmap.cend()); // OK
    mmap.begin()->second = "long";
    show_node(*(mmap.cbegin()));

    mmap.insert({ sizeof(int), "int" });
    show_node(*mmap.cbegin());

    mmap.insert({ sizeof(short), "short" });
    show_node(*mmap.cbegin());

    mmap.insert({ sizeof(char), "char" });
    show_node(*mmap.cbegin());

    mmap.insert({{ sizeof(float), "float" }, { sizeof(double), "double"}});
 
    std::cout << "mmap = { ";
    std::for_each(mmap.cbegin(), mmap.cend(), [&](const auto& n) { show_node(n, ' '); });
    std::cout << "};\n";
}

Possible output: 

{ 8, LONG }
{ 8, long }
{ 4, int }
{ 2, short }
{ 1, char }
mmap = { { 1, char } { 2, short } { 4, int } { 4, float } { 8, long } { 8, double } };

See also

returns an iterator to the end
(public member function) [edit]
returns an iterator to the beginning of a container or array
(function template) [edit]