size_typerfind(constbasic_string&str,size_typepos=npos)const; (1)(noexcept since C++11)
(constexpr since C++20)size_typerfind(constCharT*s,size_typepos,size_typecount)const; (2)(constexpr since C++20)size_typerfind(constCharT*s,size_typepos=npos)const; (3)(constexpr since C++20)size_typerfind(CharTch,size_typepos=npos)const; (4)(noexcept since C++11)
(constexpr since C++20)template<classStringViewLike>size_typerfind(constStringViewLike&t,size_typepos=npos)constnoexcept(/* see below */); (5)(since C++17)
(constexpr since C++20)Finds the last substring that is equal to the given character sequence. The search begins at pos and proceeds from right to left (thus, the found substring, if any, cannot begin in a position following pos). If
or any value not smaller than
-1 is passed as pos, the whole string will be searched.
1) Finds the last substring equal to str.
2) Finds the last substring equal to the range [s, s+count). This range can include null characters.
If [s, s+count) is not a
, the behavior is undefined.
3) Finds the last substring equal to the 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
, the behavior is undefined.
4) Finds the last character 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 substring equal to the contents of sv.
This overload participates in overload resolution only if std::is_convertible_v<constStringViewLike&,std::basic_string_view<CharT,Traits>> is true and std::is_convertible_v<constStringViewLike&,constCharT*> is false.
In all cases, equality is checked by calling
.
Parameters
str - string to search for pos - position at which to begin searching count - length of substring to search for s - pointer to a character string to search for ch - character to search for t - object (convertible to
) to search for Return value
Position of the first character of the found substring or
if no such substring is found. Note that this is an offset from the start of the string, not the end.
If searching for an empty string (i.e., str.size(), count, or Traits::length(s) is zero), the empty string is found immediately and rfind returns:
pos, if pos<size();
size() otherwise, including the case where pos==npos.
Otherwise, if
is zero,
is always returned.
Exceptions
1,4) Throws nothing.
5)
specification:
noexcept(std::is_nothrow_convertible_v<constT&,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<iomanip>#include<iostream>#include<string>voidprint(std::string::size_typen,std::string::size_typelen,std::stringconst&s){if(n==std::string::npos)std::cout<<"not found\n";elsestd::cout<<"found: "<<std::quoted(s.substr(n,len))<<" at "<<n<<'\n';}intmain(){std::string::size_typen;std::stringconsts="This is a string";// search backwards from end of stringn=s.rfind("is");print(n,2,s);// search backwards from position 4n=s.rfind("is",4);print(n,2,s);// find a single charactern=s.rfind('s');print(n,1,s);// find a single charactern=s.rfind('q');print(n,1,s);// find the prefix (see also s.starts_with("This"))n=s.rfind("This",0);print(n,4,s);}Output:
found: "is" at 5 found: "is" at 2 found: "s" at 10 not found found: "This" at 0 Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior
C++98 there was no exception safety guarantee added strong exception safety guarantee
C++11 overloads (3,4) were noexcept removed
C++17 overload (5) caused ambiguity in some cases avoided by making it a template
C++11
C++17 noexcept for overloads (4,5) were
accidently dropped by LWG2064/LWG2946 restored See also
finds the first occurrence of the given substring
(public member function)
find first occurrence of characters
(public member function)
find first absence of characters
(public member function)
find last occurrence of characters
(public member function)
find last absence of characters
(public member function)
find the last occurrence of a substring
(public member function of std::basic_string_view<CharT,Traits>)