我已经阅读了文档,并查看了示例,但我仍然无法弄清楚如何在C ++中将表分配给全局变量。我可能有点被宠坏了。我来自python并将表分配给全局变量使用mysqldb真的很简单。
是否可以将表分配给要在mysqlpp类外部访问的全局变量?
例如,当编译以下代码时,我收到错误:错误:'sched_recs'未在此范围内声明
#include <mysql++.h>
#include <string>
#include <time.h>
using namespace std;
using namespace mysqlpp;
int SSE (const char* timeStr)
{
time_t sse;
struct tm tm;
strptime(timeStr, "%Y-%m-%d %H:%M:%S", &tm);
sse = mktime(&tm);
return (sse);
}
int main()
{
string table = "sched_recs";
time_t now, tt;
now = time(NULL);
try
{
// Connect to the sample database.
mysqlpp::Connection conn(false);
// databasename, host, username, password
if (conn.connect("dbname", "dbhost", "dbusername", "dbpasswd")) {
// Retrieve a subset of the sample stock table set up by resetdb
// and display it.
//stmt = "select datetime from %s", table
mysqlpp::Query query = conn.query("select * from sched_recs");
mysqlpp::StoreQueryResult sched_recs = query.store();
//if (mysqlpp::StoreQueryResult tableData = query.store()) {
////cout << "We have:" << endl;
//}
}
}
catch (Exception& e)
{
cerr << "Exception: " << e.what() << endl;
}
for (size_t i = 0; i < sched_recs.num_rows(); ++i) {
if (SSE(sched_recs[i][1]) - 60 * 3 < now && SSE(sched_recs[i][2]) > now)
{
cout << '\t' << sched_recs[i][1] << endl;
//system("at -f test.py '18:30' today");
}
}
}
如果我改为将for循环移回到类中,那么一切正常,但这是有限的。这是唯一的方法吗?所有的例子似乎都是如此。
答案 0 :(得分:0)
正如Yaniro所说。
尝试以下代码段
#include <mysql++.h>
#include <string>
#include <time.h>
using namespace std;
using namespace mysqlpp;
int SSE (const char* timeStr)
{
time_t sse;
struct tm tm;
strptime(timeStr, "%Y-%m-%d %H:%M:%S", &tm);
sse = mktime(&tm);
return (sse);
}
int main()
{
string table = "sched_recs";
mysqlpp::StoreQueryResult sched_recs;
time_t now, tt;
now = time(NULL);
try
{
// Connect to the sample database.
mysqlpp::Connection conn(false);
// databasename, host, username, password
if (conn.connect("dbname", "dbhost", "dbusername", "dbpasswd")) {
// Retrieve a subset of the sample stock table set up by resetdb
// and display it.
//stmt = "select datetime from %s", table
mysqlpp::Query query = conn.query("select * from sched_recs");
sched_recs = query.store();
//if (mysqlpp::StoreQueryResult tableData = query.store()) {
////cout << "We have:" << endl;
//}
}
}
catch (Exception& e)
{
cerr << "Exception: " << e.what() << endl;
}
for (size_t i = 0; i < sched_recs.num_rows(); ++i) {
if (SSE(sched_recs[i][1]) - 60 * 3 < now && SSE(sched_recs[i][2]) > now)
{
cout << '\t' << sched_recs[i][1] << endl;
//system("at -f test.py '18:30' today");
}
}
}
请注意,此示例与您发布的示例之间的差异仅是名为mysqlpp::StoreQueryResult
的{{1}}变量声明的位置。
在此示例中,它在main的范围内声明,而不是try块的范围,因此在try块完成后变量的值仍然在范围内。
有关try和catch块范围的更多信息,请参阅Exception dangers and downsides。