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/C++

std::basic_string::substr

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.

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