在 sql 查詢中放置一個變量

Question

嘿伙計們，我正在嘗試將一個變量放入 sql 查詢中，但似乎無法使其正常工作。 下面是我的代碼，它是一個 RFID 閱讀器，可以讀取 rfid 標簽的值。 我希望將 rfid 標簽的值存儲在數據庫中。 如何在 sql 查詢中獲取變量 TagVal？ TagVal 變量需要位於 1e00ad0ca9 值所在的位置（下面的第二個查詢）。 謝謝！

#include <stdio.h>
#include <phidget21.h>
#include <stdlib.h>
#include <mysql/mysql.h>


int CCONV TagHandler(CPhidgetRFIDHandle RFID, void *usrptr, char *TagVal, CPhidgetRFID_Protocol proto) //Tag wordt gelezen en LED gaat aan
      {
        CPhidgetRFID_setLEDOn(RFID, 1);


printf("Tag Read: %s\n", TagVal);
return 0;
}

int CCONV TagLostHandler(CPhidgetRFIDHandle RFID, void *usrptr, char *TagVal, CPhidgetRFID_Protocol proto) //Tag is verwijderd van RFID lezer
{
     CPhidgetRFID_setLEDOn(RFID, 0);

printf("Tag Lost: %s\n", TagVal);
return 0;
 }



int rfid_simple()
{
int result;
const char *err;

//Declare an RFID handle
CPhidgetRFIDHandle rfid = 0;

//RFID object wordt aangemaakt
CPhidgetRFID_create(&rfid);

//Wanneer de tag gelezen wordt, wordt het uitgeprint
CPhidgetRFID_set_OnTag2_Handler(rfid, TagHandler, NULL);

//Wanneer de tag  verwijderd wordt, wordt het uitgeprint
CPhidgetRFID_set_OnTagLost2_Handler(rfid, TagLostHandler, NULL);

//RFID wordt geopend voor connectie
CPhidget_open((CPhidgetHandle)rfid, -1);

//Programma wacht totdat RFID is aangesloten
printf("Waiting for RFID to be attached....\n");
if((result = CPhidget_waitForAttachment((CPhidgetHandle)rfid, 10000)))
{
    CPhidget_getErrorDescription(result, &err);
    printf("Problem waiting for attachment: %s\n", err);
    return 0;
}


CPhidgetRFID_setAntennaOn(rfid, 1);

//read RFID event data
printf("RFID reader is aangesloten! Druk op enter om het programma af te sluiten\n");

//keep displaying RFID event data until user input is read
printf("RFID tag nodig\n");
getchar();


//RFID wordt afgesloten zodra er op Enter wordt gedrukt
printf("Ik ga afsluiten vriend...\n");
CPhidget_close((CPhidgetHandle)rfid);
CPhidget_delete((CPhidgetHandle)rfid);

return 0;
}

int main(int argc, char* argv[])
{
MYSQL *conn;

    char *server = "x";
    char *user = "x";
    char *password = "x";
    char *database = "x";

// Make the connection to the Mysql-database on server.
  conn = mysql_init(NULL);
if (!mysql_real_connect(conn, server,
     user, password, database, 0, NULL, 0)) {
  fprintf(stderr, "%s\n", mysql_error(conn));
  exit(1);
}

 //een insert into query : insert into tabelnaam VALUES(kolomnaam1, kolomnaam2, etc... )
 if (mysql_query(conn, "INSERT INTO Notifications(Notification_id, Notification) VALUES(NULL,'Open Deur')" )!=0)
  {exit(1);}

     if (mysql_query(conn, "INSERT INTO Access(Employee_id, Notification_id)VALUES('1e00ad0ca9',1)" )!=0)
     {exit(1);}

 /* close connection */
 mysql_close(conn);

rfid_simple();
return 0;
 }

Answer 1

您可以使用sprintf來構建您的字符串並輕松連接您的變量 - 替代 malloc/free。

  char buffer [1024];
  char *tagVal1 = "hello";
  char *tagVal2 = "world!";
  n=sprintf (buffer, "INSERT INTO Notifications(Notification_id, Notification) VALUES(%s,%s)", tagVal1, tagVal2);
  printf ("[%s] is a string %d chars long\n",buffer,n);