CODEWITHSUNDEEP
pythonc++
mirx
mirx

Reputation: 626

Translate the code from Python to C++

Now when I understand how the code works, I would like to translate it to C++.

The original Python code:

def recv_all_until(s, crlf):
    data = ""
    while data[-len(crlf):] != crlf:
        data += s.recv(1)
    return data

Here's what I tried:

std::string recv_all_until(int socket, std::string crlf)
{
    std::string data = "";
    char buffer[1];
    memset(buffer, 0, 1);


    while(data.substr(data.length()-2, data.length()) != crlf)
    {
        if ((recv(socket, buffer, 1, 0)) == 0)
        {
            if (errno != 0)
            {
                close(socket);
                perror("recv");
                exit(1);
            }
        }
        data = data + std::string(buffer);
        memset(buffer, 0, 1);
    }

    return data;
}

But it shows:

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

I understand that the problem is inside the while loop since at first the data string is empty. So how to improve this to make it work the same as it works in Python? Thank you.

Upvotes: 2

Views: 489

Answers (2)

Brian Rodriguez
Brian Rodriguez

Reputation: 4349

If we first change your Python code a bit:

def recv_all_until(s, crlf):
    data = ""
    while not data.endswith(crlf):
        data += s.recv(1)
    return data

What we need to do in C++ becomes much clearer:

bool ends_with(const std::string& str, const std::string& suffix)
{
    return str.size() >= suffix.size() &&
        std::equal(suffix.rbegin(), suffix.rend(), str.rbegin());
}

std::string recv_all_until(int socket, const std::string& crlf)
{
    std::string data = "";
    char buffer[1];
    memset(buffer, 0, 1);

    while (!ends_with(data, crlf))
    {
        if ((recv(socket, buffer, 1, 0)) == 0)
        {
            if (errno != 0)
            {
                close(socket);
                perror("recv");
                exit(1);
            }
        }
        data = data + std::string(buffer);
        memset(buffer, 0, 1);
    }

    return data;
}

Upvotes: 1

alexeykuzmin0
alexeykuzmin0

Reputation: 6440

You have the problem in the first iteration of your while loop:

Since the data is an empty string, data.length() is equal to 0, and thus you're calling data.substr(-2, 0).

To fix this, you need to add a check for the line length to the while statement.

Also, there's a method of finding such mistakes faster than writing a stackoverflow question about it. Consider reading this article.

Upvotes: 2

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