NAME¶

std::basic_string::find - std::basic_string::find

Synopsis¶

size_type find( const basic_string& (until
str, size_type pos = 0 ) const; C++11)
size_type find( const basic_string& (since
str, size_type pos = 0 ) const C++11)
noexcept; (until
C++20)
constexpr size_type find( const (since
basic_string& str, C++20)
size_type pos = 0 ) const noexcept;
size_type find( const CharT* s, (until
size_type pos, size_type count ) C++20)
const;
constexpr size_type find( const
CharT* s, (since
size_type pos, size_type count ) C++20)
const;
size_type find( const CharT* s, (until
size_type pos = 0 ) const; C++20)
constexpr size_type find( const (since
CharT* s, size_type pos = 0 ) const; (1) C++20)
size_type find( CharT ch, size_type (until
pos = 0 ) const; C++11)
(since
size_type find( CharT ch, size_type (2) C++11)
pos = 0 ) const noexcept; (until
C++20)
constexpr size_type find( CharT ch, (since
size_type pos = 0 ) const noexcept; (3) C++20)
template < class StringViewLike > (since
size_type find( const (4) C++17)
StringViewLike& t, size_type pos = 0 (until
) const noexcept(/* see below */); C++20)
template < class StringViewLike >
(5)
constexpr size_type find( const (since
StringViewLike& t, 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.
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).
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<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 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
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::basic_string_view<CharT,
Traits>>)

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

Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2064 C++11 overload (3) and (4) were noexcept removed
LWG 2946 C++17 string_view overload causes ambiguity in avoided by making it a
some cases template
P1148R0 C++11 noexcept for overload (4)/(5) was restored
C++17 accidently dropped by LWG2064/LWG2946

See also¶

strstr finds the first occurrence of a substring of characters
(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 find characters in the view
(C++17) (public member function of std::basic_string_view<CharT,Traits>)
search searches for a range of elements
(function template)