MySQL C API mysql_query

Question

I have two problems with the MySQL C API. How do I get variable to be added to the table when I do the mysql_query() and how do I get the table show decimals?

Here is my code:

void insertDataToTable(MYSQL* con, float temp, int k)
{
    mysql_query(con, "INSERT INTO Weatherstation VALUES(@k,'Temperature:', @temp)");
}

Thank you!

To send variables to the MySQL server, you should use the prepared statement API (sure, you could concatenate a string representation of its value into your SQL command—but that gives rise to the possibility of SQL injection, buggy escaping and a needless waste of resources). It's not clear what you mean by "get the table show decimals", please elaborate? — eggyal
– eggyal, Commented Sep 11, 2015 at 10:43
I send a floating point value to the Weatherstation table like this: mysql_query(con, "INSERT INTO Weatherstation VALUES(1, 'Temperature:', 124.3)"); But when I logged into the database and checked that value from the table it showed just 124 without the decimal part. — jakeheik90
– jakeheik90, Commented Sep 11, 2015 at 11:09
Oh yes of course, there is the problem! I have specified it as an integer. Thank you! — jakeheik90
– jakeheik90, Commented Sep 11, 2015 at 11:20

asio_guy · Accepted Answer · 2015-09-11 10:42:47Z

2

Try this

void insertDataToTable(MYSQL* con, float temp, int k)
{
    char query[255] ;

    sprintf( query, "INSERT INTO Weatherstation VALUES(%ld,'Temperature:', %d)", temp, k );
    mysql_query(con, query );


}

answered Sep 11, 2015 at 10:42

asio_guy

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Comments

mckenzm · Accepted Answer · 2020-04-26 09:11:21Z

0

MySQL does not support host variables that well, the previous answer shows the correct approach in building the query into a string and then using mysql_query(someconnection, string).

What is absolutely shocking is that this is not documented as much as it should be. When I had to learn this I had 30 years of DB2 and C, and I had to get this from GitHub after 2 hours of fruitless searching for "MySQL Host Variables".

You should also be aware of mysql_real_query if your query is not a conventional string and contains embedded nulls, it is passed the length of the string, but can also move a strlen() call off the server.

answered Apr 26, 2020 at 9:11

mckenzm

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