std::basic_string::find

性病：基本[医]字符串：查找

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)

查找等于给定字符序列的第一个子字符串。搜索开始于pos，即发现的子字符串不能从前面的位置开始。pos...

1%29查找第一个子字符串等于str...

2%29查找第一个子字符串等于第一个子字符串。count所指向的字符串的字符。s...s可以包含空字符。

3%29查找第一个子字符串，该子字符串等于s字符串的长度由第一个空字符决定。

4%29找到第一个字符ch%29以下的形式规则将%28视为单字符子字符串。

5%29查找第一个子字符串与String视图相等。sv...

形式上，子字符串str据说是发现就位xpos如果以下所有内容都是正确的：

xpos >= pos

xpos + str.size() <= size()

所有职位n在str，，，Traits::eq(at(xpos+n), str.at(n))

特别是，这意味着。

只有在以下情况下才能找到子字符串pos <= size() - str.size()

空子字符串位于pos当且仅当pos <= size()

对于非空子字符串，如果pos >= size()，函数总是返回npos...

参数

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

返回值

找到的子字符串或npos如果找不到这样的子字符串。

例外

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)

例

二次

#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
}

二次

产出：

二次

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

二次

另见

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)

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