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std::basic_string<CharT,Traits,Allocator>::find

From cppreference.com
< cpp‎ | string‎ | basic string
 
C++
 
Strings library
 
std::basic_string
 
size_type find( const basic_string& str, size_type pos = 0 ) const;
 (1) (noexcept since C++11)
(constexpr since C++20)
size_type find( const CharT* s, size_type pos, size_type count ) const;
 (2) (constexpr since C++20)
size_type find( const CharT* s, size_type pos = 0 ) const;
 (3) (constexpr since C++20)
size_type find( CharT ch, size_type pos = 0 ) const;
 (4) (noexcept since C++11)
(constexpr since C++20)
template< class StringViewLike >

size_type find( const StringViewLike& t,

                size_type pos = 0 ) const noexcept(/* 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 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 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 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.

Contents

[edit] 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

[edit] Return value

Position of the first character of the found substring or npos if no such substring is found.

[edit] Exceptions

1,4) Throws nothing.
5)