std::basic_string<CharT,Traits,Allocator>::find - cppreference.com (original) (raw)

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.

1. 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.

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

2. 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.

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.

[edit] Parameters

[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.

If an exception is thrown for any reason, this function has no effect (strong exception safety guarantee).

[edit] Example

#include #include #include   void print(int id, std:🧵:size_type n, std::string const& s) { std::cout << id << ") "; if (std:🧵:npos == n) std::cout << "not found! n == npos\n"; else std::cout << "found @ n = " << n << ", substr(" << n << ") = " << std::quoted(s.substr(n)) << '\n'; }   int main() { std:🧵:size_type n; std::string const s = "This is a string"; /* ^ ^ ^ 1 2 3 */   // search from beginning of string n = s.find("is"); print(1, n, s);   // search from position 5 n = s.find("is", 5); print(2, n, s);   // find a single character n = s.find('a'); print(3, n, s);   // find a single character n = s.find('q'); print(4, n, s); }

Output:

1. found @ n = 2, substr(2) = "is is a string"
2. found @ n = 5, substr(5) = "is a string"
3. found @ n = 8, substr(8) = "a string"
4. not found! n == npos

[edit] Defect reports

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

[edit] See also