NAME¶

std::basic_string::find_last_not_of - std::basic_string::find_last_not_of

Synopsis¶

size_type find_last_not_of( const basic_string& str, (noexcept since C++11)
size_type pos = npos ) (1) (constexpr since C++20)
const;
size_type find_last_not_of( const CharT* s,
size_type pos, size_type (2) (constexpr since C++20)
count ) const;
size_type find_last_not_of( const CharT* s, size_type (3) (constexpr since C++20)
pos = npos ) const;
size_type find_last_not_of( CharT ch, size_type pos = (4) (noexcept since C++11)
npos ) const; (constexpr since C++20)
template< class StringViewLike >

size_type (since C++17)
find_last_not_of( const StringViewLike& t, (5) (constexpr since C++20)

size_type pos = npos ) const
noexcept(/* see below */);

Finds the last character equal to none of the characters in the given character
sequence. The search considers only the range [0, pos]. If all characters in the
range can be found in the given character sequence, npos will be returned.

1) Finds the last character equal to none of characters in str.
2) Finds the last character equal to none of characters in the range [s, s + count).
This range can include null characters.
If [s, s + count) is not a valid range, the behavior is undefined.
3) Finds the last character equal to none of characters in character string pointed
to by s. The length of the string is determined by the first null character using
Traits::length(s).
If [s, s + Traits::length(s)) is not a valid range, the behavior is undefined.
4) Finds the last character not equal to ch.
5) Implicitly converts t to a string view sv as if by std::basic_string_view<CharT,
Traits> sv = t;, then finds the last character equal to none of characters in sv.
This overload participates in overload resolution only if
std::is_convertible_v<const StringViewLike&,
std::basic_string_view<CharT, Traits>> is true and
std::is_convertible_v<const StringViewLike&, const CharT*> is false.

In all cases, equality is checked by calling Traits::eq.

Parameters¶

str - string identifying characters to search for
pos - position at which to end search
count - length of character string identifying characters to search for
s - pointer to a character string identifying characters to search for
ch - character identifying characters to search for
t - object (convertible to std::basic_string_view) identifying characters to
search for

Return value¶

Position of the found character or npos if no such character is found.

Exceptions¶

1,4) Throws nothing.
5)
noexcept specification:
noexcept(std::is_nothrow_convertible_v<
const T&, std::basic_string_view<CharT, Traits>>)

If an exception is thrown for any reason, this function has no effect (strong
exception safety guarantee).

Example¶

// Run this code

#include <iostream>
#include <string>

void show_pos(const std::string& str, std::string::size_type found)
{
if (found != std::string::npos)
std::cout << '[' << found << "] = \'" << str[found] << "\'\n";
else
std::cout << "not found\n";
}

int main()
{
std::string str{"abc_123"};
char const* skip_set{"0123456789"};
std::string::size_type str_last_pos{std::string::npos};

show_pos(str, str.find_last_not_of(skip_set)); // [3] = '_'

str_last_pos = 2;
show_pos(str, str.find_last_not_of(skip_set, str_last_pos)); // [2] = 'c'

str_last_pos = 2;
show_pos(str, str.find_last_not_of('c', str_last_pos)); // [1] = 'b'

const char arr[]{'3', '4', '5'};
show_pos(str, str.find_last_not_of(arr)); // [5] = '2'

str_last_pos = 2;
std::string::size_type skip_set_size{4};
show_pos(str, str.find_last_not_of(skip_set,
str_last_pos,
skip_set_size)); // [2] = 'c'

show_pos(str, str.find_last_not_of("abc")); // [6] = '3'

str_last_pos = 2;
show_pos(str, str.find_last_not_of("abc", str_last_pos)); // not found
}

Output:¶

[3] = '_'
[2] = 'c'
[1] = 'b'
[5] = '2'
[2] = 'c'
[6] = '3'
not found

Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 141 C++98 overload (1) could only return npos the search range is
if pos >= size() [0, size()) in this case
LWG 847 C++98 there was no exception safety added strong exception
guarantee safety guarantee
LWG 2064 C++11 overloads (3,4) were noexcept removed
LWG 2946 C++17 overload (5) caused ambiguity in avoided by making it a
some cases template
C++11 noexcept for overloads (4,5) were
P1148R0 C++17 accidentally dropped by restored
LWG2064/LWG2946

See also¶

find finds the first occurrence of the given substring
(public member function)
rfind find the last occurrence of a substring
(public member function)
find_first_of find first occurrence of characters
(public member function)
find_first_not_of find first absence of characters
(public member function)
find_last_of find last occurrence of characters
(public member function)
find last absence of characters
find_last_not_of (public member function of std::basic_string_view<CharT,Traits>)

Category:¶

* conditionally noexcept