std :: string :: substr抛出std :: out_of_range但参数是限制的

Question

I have a vector of strings:

vector<string> tokenTotals;

When push_back is called, a string of length 41 is stored and I must operate on each element of my vector and get two substrings, the first in range 0 to 28 and the second in range 29 to 36:

for(int i = 0; i < tokenTotals.size(); i++)
{
    size_t pos = tokenTotals[i].find(": ");
    cout << tokenTotals[i] << endl; // Show all strings - OK
    cout << tokenTotals[i].length() << endl; // Lenght: 41
    string first  = tokenTotals[i].substr(0, 28); // OK
    string second = tokenTotals[i].substr(29, 36); // ERROR
    cout << first << " * " << second << endl;
}

But when I try to get the second substring, I get the following error:

terminate called after throwing an instance of std::out_of_range.
what():: basic_string::substr

Any idea of what could have happened?

Answer 1

See the std::string::substr reference . The second parameter is the length of the substring, not the position of the character after the substring, so the result is an attempt to access elements out of range - std::out_of_range is thrown.

With tokenTotals[i].substr(0, 28) this mistake doesn't manifest, since the substring has both size and the position one past end 28.

Answer 2

substr(29,36);

will attempt to get a string that starts at position 29 and has a size of 36 characters. Unfortunately 29 + 36 > 41

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