std::multimap<Key,T,Compare,Allocator>::begin, std::multimap<Key,T,Compare,Allocator>::cbegin
From cppreference.com
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
Run this code
#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
(C++11) |
returns an iterator to the end (public member function) |
(C++11)(C++14) |
returns an iterator to the beginning of a container or array (function template) |