需要帮助了解substr c ++

Question

I'm very new to programming so please correct me if I'm wrong

strand1.substr( starting position , ending position )

If I have this code:

int main()
{
    string strand1 = "abcde";
    int pos = 1;
    string strand2 = strand1.substr(0, pos);
    cout << strand2;
    _getch();
    return 0;
}

I expect this output ab

But I only got the first letter as an output a

Answer 1

As @user657267 points out in the comments, std::string::substr takes two parameters: the starting position, and the length; not the ending position.

Thus if you wish to get "ab" from "abcde", you need to have the following:

std::string strand1 = "abcde";
auto strand2 = strand1.substr(0, 2);

Answer 2

Syntax:

string.substr(start position, length of the string);

so, try this,

string strand2 = strand1.substr(0, 2);