C++ variable mysql_query to database

Question

i have goal to send data from C++ code to mariaDB. I'm struggling with compilation. Will be happy as an elephant if you can help me how to send float into database. :)

float pi=3.14; 
     if (mysql_query(conn, "INSERT INTO meranie VALUES ('%f')",pi) != 0)
  {
    fprintf(stderr, "Query Failure\n");
    return EXIT_FAILURE;
  }

Forget about the database. It's not important. You're just passing it a string. So, first, research how to build strings from variable data. Then you will probably find the answer already provided. — Asteroids With Wings, Feb 10 '20 at 21:01
The MySQL API would have been relevant had `mysql_query` supported variadic arguments to do this, but it doesn't. Though we _can_ point you towards _prepared queries_ which basically do this properly... — Asteroids With Wings, Feb 10 '20 at 21:02
What is the compilation error, which line does it refer to, what have you tried? — Michael Ribbons, Feb 10 '20 at 22:26

Patrick · Answer 1 · 2020-02-11T23:32:47.507

2

You can try (C++):

float pi=3.14;
std::string insert = "INSERT INTO meranie VALUES ("+std::to_string(pi)+")";
if (mysql_query(conn, insert.c_str()) != 0){
    fprintf(stderr, "Query Failure\n");
    return EXIT_FAILURE;
}

If you want to use only C, you can try sprintf.

edited Feb 11 '20 at 23:32

answered Feb 11 '20 at 00:07

Patrick

21
2

Welcome to StackOverflow! Please don't assume that everyone is `using namespace std;`, as that is [considered bad practice](https://stackoverflow.com/questions/1452721/why-is-using-namespace-std-considered-bad-practice) by many people. Personally, I find your code hard to read, because without the `std::` prefix, I must always ask myself whether you are referring to a function of the MySQL API or the `std` namespace. You may want to edit your answer and add the `std::` prefix or at least add the line `using namespace std;` to make it obvious what is going on. I have upvoted your answer anyway. – Andreas Wenzel Feb 11 '20 at 01:09
Thanks. I didn't use __std::__ for speed and I forgot to mention __using namespace std;__. I'm a beginner in C ++. My main specialization is Java, so thank you very much for the correction. – Patrick Feb 11 '20 at 23:53

C++ variable mysql_query to database

1 Answers1