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# std::basic_string::find

From cppreference.com
< cpp‎ | string‎ | basic string

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`.
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).
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.

### [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
sv | - | 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) (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)

### [edit] 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

### [edit] See also

strstr | finds the first occurrence of a substring of characters (function) [edit]
wcsstr | finds the first occurrence of a wide string within another wide string (function) [edit]
strchr | finds the first occurrence of a character (function) [edit]
wcschr | finds the first occurrence of a wide character in a wide string (function) [edit]
rfind | find the last occurrence of a substring (public member function) [edit]
find_first_of | find first occurrence of characters (public member function) [edit]
find_first_not_of | find first absence of characters (public member function) [edit]
find_last_of | find last occurrence of characters (public member function) [edit]
find_last_not_of | find last absence of characters (public member function) [edit]
search | searches for a range of elements (function template) [edit]

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