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std::basic_string::find(3) C++ Standard Libary std::basic_string::find(3) NAME std::basic_string::find - std::basic_string::find Synopsis size_type find( const basic_string& str, size_type pos = (1) (noex- cept since C++11) 0 ) const; (const- expr since C++20) size_type find( const CharT* s, size_type pos, size_type (2) (const- expr since C++20) count ) const; size_type find( const CharT* s, size_type pos = 0 ) (3) (const- expr since C++20) const; size_type find( CharT ch, size_type pos = 0 ) const; (4) (noex- cept since C++11) (const- expr since C++20) template< class StringViewLike > size_type find( const StringViewLike& t, (5) (since C++17) (const- expr since C++20) size_type pos = 0 ) const noexcept(/* see below */); 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 valid range, 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 valid range, the behavior is undefined. 4) Finds the first character ch (treated as a single-character sub- string by the formal rules below). 5) Implicitly converts t to a string view sv as if by std::ba- sic_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<const StringViewLike&, std::basic_string_view<CharT, Traits>> is true and std::is_convertible_v<const StringViewLike&, const CharT*> 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 npos. 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 std::basic_string_view) to search for Return value Position of the first character of the found substring or npos if no such substring is found. Exceptions 1,4) Throws nothing. 5) noexcept specification: noexcept(std::is_nothrow_convertible_v<const T&, std::ba- sic_string_view<CharT, Traits>>) If an exception is thrown for any reason, this function has no ef- fect (strong exception safety guarantee). Example // Run this code #include <iomanip> #include <iostream> #include <string> void print(int id, std::string::size_type n, std::string const& s) { std::cout << id << ") "; if (std::string::npos == n) std::cout << "not found! n == npos\n"; else std::cout << "found @ n = " << n << ", substr(" << n << ") = " << std::quoted(s.substr(n)) << '\n'; } int main() { std::string::size_type n; std::string const s = "This is a string"; /* ^ ^ ^ 1 2 3 */ // search from beginning of string n = s.find("is"); print(1, n, s); // search from position 5 n = s.find("is", 5); print(2, n, s); // find a single character n = s.find('a'); print(3, n, s); // find a single character n = 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 retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct behavior LWG 847 C++98 there was no exception safety guarantee added strong exception safety guarantee LWG 2064 C++11 overloads (3,4) were noexcept re- moved LWG 2946 C++17 overload (5) caused ambiguity in some avoided by making it a cases tem- plate P1148R0 C++11 noexcept for overloads (4,5) were re- stored C++17 accidently dropped by LWG2064/LWG2946 See also strstr finds the first occurrence of a substring of char- acters (function) finds the first occurrence of a wide string within another wide wcsstr string (function) strchr finds the first occurrence of a character (function) wcschr finds the first occurrence of a wide character in a wide string (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_not_of find last absence of characters (public member function) find characters in the view find (public member function of std::ba- sic_string_view<CharT,Traits>) search searches for a range of elements (function template) Category: * conditionally noexcept http://cppreference.com 2024.06.10 std::basic_string::find(3)
NAME | Synopsis | Parameters | Return value | Exceptions | Example | Output: | See also | Category:
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