std::basic_string::find

 

C++

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Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Strings library

Null-terminated strings

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Classes

basic_string

basic_string_view (C++17)

char_traits

 

std::basic_string

Member functions basic_string::basic_string basic_string::operator= basic_string::assign basic_string::get_allocator Element access basic_string::at basic_string::operator[] basic_string::front (C++11) basic_string::back (C++11) basic_string::data basic_string::c_str basic_string::operator basic_string_view (C++17) Iterators basic_string::beginbasic_string::cbegin (C++11) basic_string::endbasic_string::cend (C++11) basic_string::rbeginbasic_string::crbegin (C++11) basic_string::rendbasic_string::crend (C++11) Capacity basic_string::empty basic_string::sizebasic_string::length basic_string::max_size basic_string::reserve basic_string::capacity basic_string::shrink_to_fit (C++11)

Operations basic_string::clear basic_string::insert basic_string::erase basic_string::push_back basic_string::pop_back (C++11) basic_string::append basic_string::operator+= basic_string::compare basic_string::replace basic_string::substr basic_string::copy basic_string::resize basic_string::swap Search basic_string::find basic_string::rfind basic_string::find_first_of basic_string::find_first_not_of basic_string::find_last_of basic_string::find_last_not_of Constants basic_string::npos

Non-member functions operator+ operator==operator!=operator<operator>operator<=operator>= swap(std::basic_string) operator<<operator>> getline stoistolstoll (C++11)(C++11)(C++11) stoulstoull (C++11)(C++11) stofstodstold (C++11)(C++11)(C++11) to_string (C++11) to_wstring (C++11) operator""s (C++14) Helper classes hash<std::string>hash<std::wstring>hash<std::u32string>hash<std::u16string> (C++11)(C++11)(C++11)(C++11)

 

size_type find( const basic_string& str, size_type pos = 0 ) const	(1)
size_type find( const CharT* s, size_type pos, size_type count ) const;	(2)
size_type find( const CharT* s, size_type pos = 0 ) const;	(3)
size_type find( CharT ch, size_type pos = 0 ) const;	(4)
size_type find( std::basic_string_view<CharT, Traits> sv,                 size_type pos = 0) const	(5)	(since C++17)

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 as if by find(std::basic_string_view<CharT, Traits>(str), pos) (since C++17)

2) Finds the first substring equal to the first count characters of the character string pointed to by s. s can include null characters. as if by find(std::basic_string_view<CharT, Traits>(s,count),pos) (since C++17)

3) Finds the first substring equal to the character string pointed to by s as if by find(std::basic_string_view<CharT, Traits>(s), pos) (since C++17). The length of the string is determined by the first null character.

4) Finds the first character ch (treated as a single-character substring by the formal rules below).

5) Finds the first substring equal to the string view sv.

Formally, a substring str is said to be found at position xpos if all of the following is 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
sv	-	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) (none)	(until C++11)
1,4) noexcept specification:   noexcept    2,3) (none)	(since C++11) (until C++14)
1) noexcept specification:   noexcept    2,3,4) (none)	(since C++14)
5) noexcept specification:   noexcept	(since C++17)

Example

Run this code

#include <string>
#include <iostream>
 
void print(std::string::size_type n, std::string const &s)
{
    if (n == std::string::npos) {
        std::cout << "not found\n";
    } else {
        std::cout << "found: " << s.substr(n) << '\n';
    }
}
 
int main()
{
    std::string::size_type n;
    std::string const s = "This is a string";
 
    // search from beginning of string
    n = s.find("is");
    print(n, s);
 
    // search from position 5
    n = s.find("is", 5);
    print(n, s);
 
    // find a single character
    n = s.find('a');
    print(n, s);
 
    // find a single character
    n = s.find('q');
    print(n, s);
}

Output:

found: is is a string
found: is a string
found: a string
not found

See also

strstr	finds the first occurrence of a substring of characters (function)
wcsstr	finds the first occurrence of a wide string within another wide 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)
search	searches for a range of elements (function template)