C program to add data to MYSQL database - No results added - mysql

Question

I'm trying to build a C-program to add data to my MYSQL database and I would like to use variables within the SQL string. I want to insert UNIX time (epoch) in one column and the result from an energy meter into the other (double)
Even though it builds without errors or warnings I can't get it to insert the data into the table. Can someone give me a hint of where to look?
Thankful for all help I can get as I'm pretty much fumbling in the dark
Regards,
Mikael
#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <time.h>
#include <math.h>
#include <mysql.h>
#include <my_global.h>
#include <stdlib.h> // For exit function
int loggingok; // Global var indicating logging on or off
double result = 323.234567; //Debug
double actual_time_sec;
void calculate_watts(void)
{
MYSQL *conn = mysql_init(NULL);
char *server = "localhost";
char *user = "root";
char *password = "password"; /* set me first */
char *database = "power";
char SQL_String[100];
char time_char[11];
char result_char[11];
time_t actual_time;
actual_time = time(0);
actual_time_sec = difftime(actual_time,0);
sprintf(time_char,"%g",actual_time_sec);
sprintf(result_char,"%g",result);
printf("Tid: %g\n",actual_time_sec); //Debug
printf("Resultat: %g\n", result); //Debug
strcpy(SQL_String, "INSERT INTO consumption(time,consumption) VALUES(");
strcat(SQL_String, time_char);
strcat(SQL_String, ",");
strcat(SQL_String, result_char);
strcat(SQL_String, ")");
printf("SQL: %s", SQL_String); //Debug
// SQL_String = "INSERT INTO consumption(time,consumption) VALUES('"+ actual_time_sec +"',"+ result +")";
if (!mysql_real_connect(conn, server, user, password, database, 0, NULL, 0)) {
fprintf(stderr, "%s\n", mysql_error(conn));
exit(1); }
if (mysql_query(conn, SQL_String)) {
fprintf(stderr, "%s\n", mysql_error(conn));
exit(1); }
}
int main (int argc, char *argv[])
{
printf(argv[1]); //Debug
if(strcmp(argv[1], "db")) {
loggingok=1;
printf("Efergy E2 Classic decode \n\n");
calculate_watts(); }
else {
loggingok=0; }
return 0;
}

Answer 1

here is a great example...
http://php.net/mysql_query. Note the usage of sprintf here. The 2nd and 3rd parameters work with the sprintf to place the data in these 2 parameters exactly where they are needed in the SQL statement.
$query = sprintf("SELECT firstname, lastname, address, age FROM friends
WHERE firstname='%s' AND lastname='%s'",
mysql_real_escape_string($firstname),
mysql_real_escape_string($lastname));
// Perform Query
$result = mysql_query($query);
// Check result
// This shows the actual query sent to MySQL, and the error. Useful for debugging.
if (!$result) {
$message = 'Invalid query: ' . mysql_error() . "\n";
$message .= 'Whole query: ' . $query;
die($message);
}
Please note the usage of if (!$result) this allows you to do a quick validation of if you have success or not. If an error is found the text resturned from mysql_error is placed in the message variable and then presented when the app dies.