• Log in

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.

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

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

[edit] Example

#include <iomanip>
#include <iostream>
#include <string>
 
void print(int id, std::string::size_type n, std::string const& s)
{
 std::cout << id << ") ";
 if (std::string::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::string::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);
}

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

• In other languages

• Deutsch
• Español
• Français
• Italiano
• 日本語
• Português
• Русский
• 中文