C language variable type float and integer pass in mysql - mysql

Question

I'm a beginner in C and mysql programing.For some days now I am trying to write float and integer values that i get from sensors to a database in mySQL.So far i'm just getting an error "too many arguments to function ‘mysql_query’" and " expected ‘const char *’".Below is my simple code.
int main()
{
int var1 = 1;
float var2 = 5.1;
MYSQL *conn;
MYSQL_RES *res;
MYSQL_ROW row;
conn = mysql_init(NULL);
if (!mysql_real_connect(conn, host, user, pass, dbname,port, unix_socket, flag))
{
fprintf(stderr, "\nError: %s [%d]\n",mysql_error(conn),mysql_errno(conn));
exit(1);
}
printf("Connection successful!\n");
mysql_query(conn,"INSERT INTO variables (var1) VALUE ('%d');",var1);
mysql_query(conn, mysql_query );
}

Answer 1

It's a nice idea, but mysql_query doesn't work with variable arguments.
You need to store the query in a buffer:
char buff[1024];
snprintf(buff, sizeof buff, "INSERT INTO variables (var1) VALUES ('%d');",var1);
and then you can call mysql_query with this buffer:
mysql_query(conn, buff);
EDIT:
As pointed out by #PaulOgilvie: Notice VALUES instead of VALUE in the query.

Answer 2

You should use a prepared statement, which would also take care of the types and all that (assuming conn is a valid connection object)
MYSQL_STMT *stmt;
MYSQL_BIND params[1];
const char *query;
// This is necessary or the program will crash
memset(params, 0, sizeof(params));
query = "INSERT INTO variables (var1) VALUES (?)";
stmt = mysql_stmt_init(conn);
params[0].buffer = &var1;
params[0].buffer_type = MYSQL_TYPE_LONG;
if (stmt == NULL)
exit(1); // Ideally handle the error and solve the problem
// but for simplicity ...
if (mysql_stmt_prepare(stmt, query, strlen(query)) != 0)
exit(1);
if (mysql_stmt_bind_param(stmt, params) != 0)
exit(1);
if (mysql_stmt_execute(stmt) != 0) {
// Ideally print mysql's error
fprintf(stderr, "an error occurred\n");
}
mysql_stmt_close(stmt);
This is the good safe way to do this, and also you can reuse the prepared statement as many times as you want and they promise it will be faster and more efficient because the query is prepared so the execution plan is known and you don't need to use the snprintf() which by the way should be checked for errors and also, you should check if the query did fit into the target array, read the documentation for that.
Also, you don't need to worry about escaping strings or anything. It will all be handled transparently for you. As long as you use the correct type and of course, specify the length of strings.
Note that you can bind parameters and results too in SELECT queries.

Answer 3

Are you sure you don't need "VALUES" here instead of "VALUE":
mysql_query(conn,"INSERT INTO variables (var1) VALUE ('%d');",var1);