std::basic_string::substr

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< cpplrm; | stringlrm; | basic string
std::basic_string
basic_string substr( size_type pos = 0,
size_type count = npos ) const;

Returns a substring [pos, pos+count). If the requested substring extends past the end of the string, or if count == npos, the returned substring is [pos, size()).

Parameters

pos - position of the first character to include
count - length of the substring

Return value

String containing the substring [pos, pos+count).

Exceptions

std::out_of_range if pos > size()

Complexity

Linear in count

Notes

The returned string is constructed as if by basic_string(data()+pos, count), which implies that the returned string's allocator will be default-constructed the new allocator will not be a copy of this->get_allocator().

Example

#include <string>
#include <iostream>

int main()
{
    std::string a = "0123456789abcdefghij";

    // count is npos, returns [pos, size())
    std::string sub1 = a.substr(10);
    std::cout << sub1 << '\n';

    // both pos and pos+count are within bounds, returns [pos, pos+count)
    std::string sub2 = a.substr(5, 3);
    std::cout << sub2 << '\n';

    // pos is within bounds, pos+count is not, returns [pos, size()) 
    std::string sub4 = a.substr(a.size()-3, 50);
    std::cout << sub4 << '\n';

    try {
        // pos is out of bounds, throws
        std::string sub5 = a.substr(a.size()+3, 50);
        std::cout << sub5 << '\n';
    } catch(const std::out_of_range& e) {
        std::cout << "pos exceeds string size\n";
    }
}

Output:

abcdefghij
567
hij
pos exceeds string size

See also

copies characters
(public member function)
returns the number of characters
(public member function)
find characters in the string
(public member function)