嵌入C++的C++
嵌入C++的C++
提问于 2017-04-20 02:51:11
当涉及到在C++中使用C++时，我遇到了一个问题。
这可能是我忽略的小东西，但在我的第一个while循环中，rowFlight[0]保存的是flightnum (数字介于1-5之间)。
我试图在我的第二个查询mysql_query(connection ,"SELECT firstName, lastName FROM passenger, manifest, flight WHERE passenger.passnum = manifest.passnum AND manifest.flightnum = flight.flightnum AND flight.flightnum = '*rowFlight[0]';");中使用它
但什么都没有归还。当我在查询后使用mysql_num_rows查看返回了多少行时，它会显示0，但是当我硬编码查询中的值(介于1到5之间)而不是使用*rowFlight[0]时，我确实会得到返回的行(我希望看到的行)。
在另一个查询中使用查询结果的正确方法是什么？
#include <iostream>
#include <iomanip>
#include <mysql.h>
using std::cout; using std::cerr;
using std::setw; using std::endl;
int main() {
MYSQL *connection, mysql;
connection = mysql_init(&mysql); //initialize instance
connection = mysql_real_connect(connection, SERVER, USER, PASSWORD, DATABASE, 0, NULL, 0);
if(connection) { //if connected successfully
MYSQL_RES *returnValFlight; //pointer to receive the return value
MYSQL_ROW rowFlight; //variable for rows
mysql_query(connection ,"SELECT * FROM flight;"); //Pull all the flights (flightnum, origination, destination, miles)
returnValFlight = mysql_store_result(connection); //returnVal is a temporary file for the results of the query, a cursor
MYSQL_RES *returnValPassenger; //pointer to receive the return value
MYSQL_ROW rowPassenger; //variable for rows
cout << endl
<< "Flight Number: Flight Origination: Flight Destination: Miles:" << endl
<< "--------------------------------------------------------------------------" << endl;
while ((rowFlight = mysql_fetch_row(returnValFlight)) != NULL) { //while not end of the cursor
cout << rowFlight[0] << rowFlight[1] << rowFlight[2] << rowFlight[3] << endl; //print flight info
mysql_query(connection ,"SELECT firstName, lastName FROM passenger, manifest, flight WHERE passenger.passnum = manifest.passnum AND manifest.flightnum = flight.flightnum AND flight.flightnum = '*rowFlight[0]';"); //query
returnValPassenger = mysql_store_result(connection); //returnVal is a temporary file for the results of the query, a cursor
while ((rowPassenger = mysql_fetch_row(returnValPassenger)) != NULL) //while not end of the cursor
cout << rowPassenger[0] << " " << rowPassenger[1] << endl; //print passengers on that flight
}
cout << endl;
mysql_free_result(returnValPassenger);
mysql_free_result(returnValFlight);
mysql_close(connection); //close connection
}
else //connection failed
cerr << "Connection Failed!" << endl;
return 0;
}回答 1
Stack Overflow用户
回答已采纳
发布于 2017-04-20 20:20:54
修复了问题，能够在查询中使用rowFlight[0]。
while ((rowFlight = mysql_fetch_row(returnValFlight)) != NULL) { //while not end of the cursor
cout << setw(7) << rowFlight[0] << setw(24) << rowFlight[1] << setw(22) << rowFlight[2] << setw(18) << rowFlight[3] << endl << endl; //print flight info (flightnum, origination, destination, miles))
ostringstream os;
os << "SELECT firstName, lastName FROM passenger, manifest WHERE passenger.passnum = manifest.passnum AND manifest.flightnum =" << rowFlight[0]; //pull all passengers on that flight
mysql_query(connection, os.str().c_str());
returnValPassenger = mysql_store_result(connection); //returnVal is a temporary file for the results of the query, a cursor
cout << setw(50) << "List Of Passengers On Flight Number " << rowFlight[0] << endl //current flight number
<< setw(50) << "Total Passengers -> " << mysql_num_rows(returnValPassenger) << endl << endl; //how mnay passengers on that flight?
while ((rowPassenger = mysql_fetch_row(returnValPassenger)) != NULL) //while not end of the cursor
cout << setw(35) << rowPassenger[0] << " " << rowPassenger[1] << endl; //print passengers on that flight
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/43509378
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