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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将表分配给 C++ 中的全局变量。我可能有点被宠坏了。我来自 python,使用 mysqldb 将表分配给全局变量确实是一件简单的事情。

可以将表分配给全局变量以在 mysqlpp 类之外访问吗?

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");
    }
  }

}

如果我将 for 循环移回类中,则一切正常,但这是有限的。这是唯一的方法吗?所有的例子似乎都使它看起来如此。

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1 回答 1

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正如亚尼罗建议的那样。

试试下面的代码片段

#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的唯一区别是mysqlpp::StoreQueryResult名为 的变量的声明位置sched_recs

在这个示例中,它是在 main 的范围内声明的,而不是在 try 块的范围内,因此在 try 块完成后变量的值仍在范围内。

有关 try 和 catch 块范围的更多信息,请参阅异常危险和缺点

于 2012-03-15T12:12:28.570 回答