mysql with c program - mysql

Question

I wrote a program in c language with mysql.
It does not work well.
I create a connect function to help me connect mysql
MYSQL *ts_mysql_connect(char *host, char *user, char *pass, char *database)
{
MYSQL *conn = mysql_init(NULL);
fprintf(stderr, "[ts_mysql_connect] conn-> %ld\n", conn);
if (!mysql_real_connect(conn, host, user, pass, database, 0, NULL, 0)){
fprintf(stderr, "%s\n", mysql_error(conn));
exit(1);
}
//set auto commit to false
if (mysql_autocommit(conn, 0))
fprintf(stderr, "%s\n", "SET MYSQL autocommit to off faild!");
fprintf(stderr, "[ts_mysql_connect] conn-> %ld\n", conn);
return conn;
}
and I use below the code below to call my function
MYSQL *test;
test = ts_mysql_connect(conf->run_conf->mysql_host,
conf->run_conf->mysql_user,
conf->run_conf->mysql_pass,
conf->run_conf->mysql_database);
conf->mysql_start = time(NULL);
if (verbose)
fprintf(stderr, "[ts_mysql_insert] mysql conn init at %ld\n",
&test);
exit(1);
i donot know why ts_mysql_connect return different address of the conn.
run log:
[ts_mysql_connect] conn-> 140065527302336
[ts_mysql_connect] conn-> 140065527302336
[ts_mysql_insert] mysql conn init at -1946154816
So why MYSQL *conn in [ts_mysql_insert] and [ts_mysql_connect] have different address

Answer 1

You didn't declare the function prototype of ts_mysql_connect in the second program, so the compiler assumes that the function returns an int type.
If you use -Wall directive to enable all warnings, you will see a warning message like this:
warning: implicit declaration of function ‘ts_mysql_connect’

Answer 2

#include <stdio.h>
#include <stdlib.h>
#include <my_global.h>
#include <mysql.h>
MYSQL *DatabaseConnection;
const char *ServerName = "192.168.1.12";
const char *User = "dbuser";
const char *Password = "dbpassword";
const char *Name = "test";
const char *DB_Socket_Path = "/var/run/mysqld/mysql.sock";
int execute_db_query(const char *sql_query)
{
MYSQL_RES *result = NULL;
MYSQL_ROW row;
int num_fields;
int i;
if (!DatabaseConnection)
return -1;
mysql_query(DatabaseConnection, sql_query);
result = mysql_store_result(DatabaseConnection);
if(result == NULL)
{
mysql_free_result(result);
return -1;
}
if (!result->eof) {
mysql_free_result(result);
return -1;
}
num_fields = mysql_num_fields(result);
int f_count = result->field_count;
int index =1 ;
while ((row = mysql_fetch_row(result))) {
for (i = 0; i < num_fields; i++) {
printf("%s ", row[i] ? row[i] : "NULL");
}
printf("\n");
index++;
}
mysql_free_result(result);
return 0;
}
void close_db_connection() {
mysql_close(DatabaseConnection);
mysql_library_end();
}
int init_connect() {
DatabaseConnection = mysql_init(NULL);
printf("MySQL client version: %s\n", mysql_get_client_info());
if (!mysql_real_connect(DatabaseConnection, ServerName, User, Password,
Name, 0, DB_Socket_Path, 0)) {
puts(mysql_error(DatabaseConnection));
close_db_connection();
return -1;
}
printf("Host : %s \n", mysql_get_host_info(DatabaseConnection));
printf("Server : %s: \n", mysql_get_server_info(DatabaseConnection));
printf("Protocol : %d\n", mysql_get_proto_info(DatabaseConnection));
return 0;
}
int main(void) {
puts("SQL Example");
init_connect() ;
execute_db_query("select * from test");
return EXIT_SUCCESS;
}
I see you are using socket less connection so you can pass NULL in this case.