std::basic_string::find

size_type find( const basic_string& str, size_type pos = 0 ) const;

size_type find( const CharT* s, size_type pos, size_type count ) const;

size_type find( const CharT* s, size_type pos = 0 ) const;

size_type find( CharT ch, size_type pos = 0 ) const;

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 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.

Parameters

Return value

Position of the first character of the found substring or npos if no such substring is found.

Exceptions

Example

#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);
}

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

See also