Finds the first substring equal to the given character sequence. Search begins atpos, i.e. the found substring must not begin in a position precedingpos.

Formally, a substringstr is said to befound at positionxpos if all of the following aretrue:

• xpos>= pos
• xpos+ str.size()<= size()
• for all positionsn instr,Traits::eq(at(xpos+ n), str.at(n)).

In particular, this implies that

• a substring can be found only ifpos<= size()- str.size()
• an empty substring is found atpos if and only ifpos<= size()
• for a non-empty substring, ifpos>= size(), the function always returnsnpos.

[edit]Parameters

[edit]Return value

Position of the first character of the found substring ornpos 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::stringconst& s){std::cout<< id<<") ";if(std::string::npos== n)std::cout<<"not found! n == npos\n";elsestd::cout<<"found @ n = "<< n<<", substr("<< n<<") = "<<std::quoted(s.substr(n))<<'\n';} int main(){    std::string::size_type n;std::stringconst 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

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