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Returns a reference to the first element in the forward_list container.
Unlike member forward_list::begin, which returns an iterator to this same element, this function returns a direct reference.
Calling this function on an empty container causes undefined behavior.
If the forward_list object is const-qualified, the function returns a const_reference. Otherwise, it returns a reference.
Member types reference and const_reference are the reference types to the elements of the forward_list container (see member types).
Output:
The first element is potentially accessed or modified by the caller. Concurrently accessing or modifying other elements is safe.
Otherwise, it causes undefined behavior.
Reference
C library:
- <cassert> (assert.h)
- <cctype> (ctype.h)
- <cerrno> (errno.h)
-
<cfenv> (fenv.h)C++11
- <cfloat> (float.h)
-
<cinttypes> (inttypes.h)C++11
- <ciso646> (iso646.h)
- <climits> (limits.h)
- <clocale> (locale.h)
- <cmath> (math.h)
- <csetjmp> (setjmp.h)
- <csignal> (signal.h)
- <cstdarg> (stdarg.h)
-
<cstdbool> (stdbool.h)C++11
- <cstddef> (stddef.h)
-
<cstdint> (stdint.h)C++11
- <cstdio> (stdio.h)
- <cstdlib> (stdlib.h)
- <cstring> (string.h)
-
<ctgmath> (tgmath.h)C++11
- <ctime> (time.h)
-
<cuchar> (uchar.h)C++11
- <cwchar> (wchar.h)
- <cwctype> (wctype.h)
Containers:
-
<array>C++11
- <deque>
-
<forward_list>C++11
- <list>
- <map>
- <queue>
- <set>
- <stack>
-
<unordered_map>C++11
-
<unordered_set>C++11
- <vector>
-
Input/Output:
Multi-threading:
-
<atomic>C++11
-
<condition_variable>C++11
-
<future>C++11
-
<mutex>C++11
-
<thread>C++11
-
Other:
- <algorithm>
- <bitset>
-
<chrono>C++11
-
<codecvt>C++11
- <complex>
- <exception>
- <functional>
-
<initializer_list>C++11
- <iterator>
- <limits>
- <locale>
- <memory>
- <new>
- <numeric>
-
<random>C++11
-
<ratio>C++11
-
<regex>C++11
- <stdexcept>
- <string>
-
<system_error>C++11
-
<tuple>C++11
-
<type_traits>C++11
-
<typeindex>C++11
- <typeinfo>
- <utility>
- <valarray>
<forward_list>
-
forward_listC++11
forward_list
-
forward_list::~forward_listC++11
-
forward_list::forward_listC++11
member functions
-
forward_list::assignC++11
-
forward_list::before_beginC++11
-
forward_list::beginC++11
-
forward_list::cbefore_beginC++11
-
forward_list::cbeginC++11
-
forward_list::cendC++11
-
forward_list::clearC++11
-
forward_list::emplace_afterC++11
-
forward_list::emplace_frontC++11
-
forward_list::emptyC++11
-
forward_list::endC++11
-
forward_list::erase_afterC++11
-
forward_list::frontC++11
-
forward_list::get_allocatorC++11
-
forward_list::insert_afterC++11
-
forward_list::max_sizeC++11
-
forward_list::mergeC++11
-
forward_list::operator=C++11
-
forward_list::pop_frontC++11
-
forward_list::push_frontC++11
-
forward_list::removeC++11
-
forward_list::remove_ifC++11
-
forward_list::resizeC++11
-
forward_list::reverseC++11
-
forward_list::sortC++11
-
forward_list::splice_afterC++11
-
forward_list::swapC++11
-
forward_list::uniqueC++11
-
non-member overloads
public member function
<forward_list>
std::forward_list::front
reference front();const_reference front() const;
Access first element
Unlike member forward_list::begin, which returns an iterator to this same element, this function returns a direct reference.
Calling this function on an empty container causes undefined behavior.
Parameters
noneReturn value
A reference to the first element in the container.If the forward_list object is const-qualified, the function returns a const_reference. Otherwise, it returns a reference.
Member types reference and const_reference are the reference types to the elements of the forward_list container (see member types).
Example
|
|
Output:
mylist now contains: 11 16 77 |
Complexity
Constant.Iterator validity
No changes.Data races
The container is accessed (neither the const nor the non-const versions modify the container).The first element is potentially accessed or modified by the caller. Concurrently accessing or modifying other elements is safe.
Exception safety
If the container is not empty, the function never throws exceptions (no-throw guarantee).Otherwise, it causes undefined behavior.
See also
- forward_list::begin
- Return iterator to beginning (public member type)
- forward_list::before_begin
- Return iterator to before beginning (public member function)
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© cplusplus.com, 2000-2025 - All rights reserved - v3.3.4s
Spotted an error? contact us