From cppreference.com
size_typefind(constbasic_string&str,size_typepos=0)const; (1)(noexcept since C++11)
(constexpr since C++20)size_typefind(constCharT*s,size_typepos,size_typecount)const; (2)(constexpr since C++20)size_typefind(constCharT*s,size_typepos=0)const; (3)(constexpr since C++20)size_typefind(CharTch,size_typepos=0)const; (4)(noexcept since C++11)
(constexpr since C++20)template<classStringViewLike>size_typefind(constStringViewLike&t,size_typepos=0)constnoexcept(/* see below */); (5)(since C++17)
(constexpr since C++20)Finds the first substring equal to the given character sequence. Search begins at pos, i.e. the found substring must not begin in a position preceding pos.
1) Finds the first substring equal to str.
2) Finds the first substring equal to the range [s, s+count). This range may contain null characters.
If [s, s+count) is not a
, the behavior is undefined.
3) Finds the first 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 first character ch (treated as a single-character substring by the formal rules below).
5) Implicitly converts t to a string view sv as if by std::basic_string_view<CharT,Traits>sv=t;, then finds the first substring equal to 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.
Formally, a substring str is said to be found at position xpos if all of the following are true:
xpos>=pos
xpos+str.size()<=size()
for all positions n in str, Traits::eq(at(xpos+n),str.at(n)).
In particular, this implies that
a substring can be found only if pos<=size()-str.size()
an empty substring is found at pos if and only if pos<=size()
for a non-empty substring, if pos>=size(), the function always returns
.
Parameters
str - string to search for pos - position at which to start the search 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.
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(intid,std::string::size_typen,std::stringconst&s){std::cout<<id<<") ";if(std::string::npos==n)std::cout<<"not found! n == npos\n";elsestd::cout<<"found @ n = "<<n<<", substr("<<n<<") = "<<std::quoted(s.substr(n))<<'\n';}intmain(){std::string::size_typen;std::stringconsts="This is a string";/* ^ ^ ^ 1 2 3 */// search from beginning of stringn=s.find("is");print(1,n,s);// search from position 5n=s.find("is",5);print(2,n,s);// find a single charactern=s.find('a');print(3,n,s);// find a single charactern=s.find('q');print(4,n,s);}Output:
1) found @ n = 2, substr(2) = "is is a string" 2) found @ n = 5, substr(5) = "is a string" 3) found @ n = 8, substr(8) = "a string" 4) not found! n == npos 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 a substring of characters
(function)
finds the first occurrence of a wide string within another wide string
(function)
finds the first occurrence of a character
(function)
finds the first occurrence of a wide character in a wide string
(function)
find the last occurrence of a 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 characters in the view
(public member function of std::basic_string_view<CharT,Traits>)
searches for the first occurrence of a range of elements
(function template & algorithm function object)
(C++20)