std::basic_string::find

 

C++

Language

Standard library headers

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Utilities library

Strings library

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Algorithms library

Iterators library

Numerics library

Input/output library

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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

Byte strings

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Wide strings

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 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) 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)

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 first count characters of the character string pointed to by s. s can include null characters.

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.

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

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

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)

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)