trying to get Database Programming with C/C++, by Manoj Debnath July 11, 2016

trying to get Database Programming with C/C++, by Manoj Debnath July 11, 2016, to work, but having issues with getting basic part to run. db_conn is not zero, and db_conn->host results in Access to field 'host' results in a dereference of a null pointer.

Code:

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CBankTransaction::CBankTransaction(const std::string HOST, const std::string USER,
                                  const std::string PASSWORD,
                                  const std::string DATABASE)
{
    db_conn = mysql_init(NULL);
    if(db_conn)
    {
        db_conn = mysql_real_connect(db_conn, HOST.c_str(), USER.c_str(),
                                PASSWORD.c_str(), DATABASE.c_str(), 0, NULL, 0);
        std::cout << "1: if(!db_conn) \n";
    }
    else
    {
        std::cout << "1: else \n";
        std::cout <<"db_conn->host = " << db_conn->host << '\n';
    }

    if(!db_conn)
    {
        std::cout << "2: if(!db_conn) \n";
        std::cout <<"db_conn->host = " << db_conn->host << '\n';
    }
    else
    {
        std::cout << "2: else \n";
        std::cout <<"db_conn->host = " << db_conn->host << '\n';
    }

}

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both:

Code:

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db_conn = mysql_init(NULL);
    if(!db_conn)

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and

Code:

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db_conn = mysql_init(NULL);
    if(db_conn)

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result in trying to access a null pointer.
is mysql server suppose to be started from outside of program?
is there suppose to be a folder made somewhere, before program is run?
something i am missing that was stated on https://www.codeguru.com/database/da...ming-with-c-c/ ?

I found "Errors In case of insufficient memory, NULL is returned. "
how to set memory, and why was it not included in example?

Quote:

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Originally Posted by micha_eleric

how to set memory, and why was it not included in example?

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DId you try to ask the author of the article?

Quote:

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Originally Posted by VictorN

DId you try to ask the author of the article?

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could not find how to ask author, which was the first thing i looked for.

Code:

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        db_conn = mysql_real_connect(db_conn, HOST.c_str(), USER.c_str(),
                                PASSWORD.c_str(), DATABASE.c_str(), 0, NULL, 0);

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The problem here is you trash your db_conn if the connect fails.
You can't go forward, you can't go back, you can't find out what happened.

Use something like this.

Code:

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if (!mysql_real_connect(db_conn, HOST.c_str(), USER.c_str(),
                                PASSWORD.c_str(), DATABASE.c_str(), 0, NULL, 0))
{
    std::cerr << "Failed to connect to database: Error: " << mysql_error(db_conn) << '\n';
}

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Then you can look up the error on the man page and figure out why it didn't work.
https://dev.mysql.com/doc/c-api/8.0/...l-connect.html