我遇到了线程问题，我一直试图在SO和Google上找到答案，但没有运气。
简单地说，我想创建一个可以执行一个函数的线程，该函数使用另一个函数作为参数（带有自己的参数 - 见下文）。
我已经按照这些指南（https://www.justsoftwaresolutions.co.uk/threading/multithreading-in-c++0x-part-2-function-objects-and-arguments.html）对线程进行了完美无缺的处理，除了上面提到的用例。
这是我尝试创建线程的特定行：
std::thread t(executeQuery, buildQuery(*_mVecHistIter, symbol));
这些是嵌套函数定义：
std::wstring database_con::buildQuery(vector<std::wstring> input, string symbol)
void database_con::executeQuery(wstring query)
错误：
没有构造函数的实例＆＃34; std :: thread :: thread＆＃34;匹配参数 列表
我可以简单地重建这些函数，以便buildQuery启动executeQuery。但是我想分开这些电话并确保尽可能多地从班级＆＃34; body＆＃34;为了便于阅读和维护。
任何有关该主题的更多资料的建议，指示或想法都将不胜感激！ ：）
我正在使用 MSVC 2015。
修改
#include "stdafx.h"
#include "database_con.h"
////////////////////////////////////////////////////////////////////////
// Show errors from the SQLHANDLE
void database_con::show_error(unsigned int handletype, const SQLHANDLE& handle)
{
SQLWCHAR sqlstate[1024];
SQLWCHAR message[1024];
if (SQL_SUCCESS == SQLGetDiagRec(handletype, handle, 1, sqlstate, NULL, message, 1024, NULL))
wcout << "Message: " << message << "\nSQLSTATE: " << sqlstate << endl;
}
std::wstring database_con::StringToWString(const std::string& s)
{
std::wstring temp(s.length(), L' ');
std::copy(s.begin(), s.end(), temp.begin());
return temp;
}
////////////////////////////////////////////////////////////////////////
// Builds the stored procedure query.
std::wstring database_con::buildQuery(vector<std::wstring> input, string symbol)
{
std::wstringstream builder;
builder << L"EXEC sp_addHistorical " << "@Symbol='" << L"" << StringToWString(symbol) << "'," <<
"@Date='" << (wstring)L"" << input.at(0) << "'," <<
"@Open=" << (wstring)L"" << input.at(1) << "," <<
"@Close=" << (wstring)L"" << input.at(2) << "," <<
"@MaxPrice=" << (wstring)L"" << input.at(3) << "," <<
"@MinPrice=" << (wstring)L"" << input.at(4) << "," <<
"@Volume=" << (wstring)L"" << input.at(5) << ";";
return builder.str();
}
void database_con::executeQuery(wstring query) {
if (SQL_SUCCESS != SQLExecDirectW(stmt, const_cast<SQLWCHAR*>(query.c_str()), SQL_NTS)) {
std::cout << "Execute error " << std::endl;
show_error(SQL_HANDLE_STMT, stmt);
std::wcout << L"Unsuccessful Query: " << query << std::endl;
}
// Close Cursor before next iteration starts:
SQLRETURN closeCursRet = SQLFreeStmt(stmt, SQL_CLOSE);
if (!SQL_SUCCEEDED(closeCursRet))
{
show_error(SQL_HANDLE_STMT, stmt);
// maybe add some handling for the case that closing failed.
}
}
////////////////////////////////////////////////////////////////////////
// Constructs a database connector object with the historical data and its symbol
database_con::database_con(std::vector<std::vector<std::wstring>> historical, string symbol){
/*
Set up the handlers
*/
/* Allocate an environment handle */
SQLAllocHandle(SQL_HANDLE_ENV, SQL_NULL_HANDLE, &env);
/* We want ODBC 3 support */
SQLSetEnvAttr(env, SQL_ATTR_ODBC_VERSION, (void *)SQL_OV_ODBC3, 0);
/* Allocate a connection handle */
SQLAllocHandle(SQL_HANDLE_DBC, env, &dbc);
/* Connect to the DSN */
SQLDriverConnectW(dbc, NULL, L"DRIVER={SQL Server};SERVER=ERA-PC-STUART\\JBK_DB;DATABASE=master;UID=geo;PWD=kalle123;", SQL_NTS, NULL, 0, NULL, SQL_DRIVER_COMPLETE);
/* Check for success */
if (SQL_SUCCESS != SQLAllocHandle(SQL_HANDLE_STMT, dbc, &stmt))
{
show_error(SQL_HANDLE_DBC, dbc);
std::cout << "Failed to connect";
}
std::cout << "Building and executing the query" << std::endl;
for (_mVecHistIter = historical.begin();
_mVecHistIter != historical.end();
_mVecHistIter+5) {
std::thread t(&database_con::executeQuery, *this, buildQuery(*_mVecHistIter, symbol));
std::thread t2(&database_con::executeQuery, *this, buildQuery(*_mVecHistIter, symbol));
std::thread t3(&database_con::executeQuery, *this, buildQuery(*_mVecHistIter, symbol));
std::thread t4(&database_con::executeQuery, *this, buildQuery(*_mVecHistIter, symbol));
std::thread t5(&database_con::executeQuery, *this, buildQuery(*_mVecHistIter, symbol));
t.join();
t2.join();
t3.join();
t4.join();
t5.join();
//executeQuery(buildQuery(*_mVecHistIter, symbol));
}
/*_mSymbol = symbol;
std::wstringstream stream(StringToWString(historical));
std::wstring line;
int row = 0;
while (std::getline(stream, line)) {
if (row > 0) {
vector<wstring> vHistorical = parseData(L"" + line, ',');
std::wstring SQL = buildQuery(vHistorical, _mSymbol);
if (SQL_SUCCESS != SQLExecDirectW(stmt, const_cast<SQLWCHAR*>(SQL.c_str()), SQL_NTS)) {
std::cout << "Execute error " << std::endl;
show_error(SQL_HANDLE_STMT, stmt);
std::wcout << L"Unsuccessful Query: " << SQL << std::endl;
}
// Close Cursor before next iteration starts:
SQLRETURN closeCursRet = SQLFreeStmt(stmt, SQL_CLOSE);
if (!SQL_SUCCEEDED(closeCursRet))
{
show_error(SQL_HANDLE_STMT, stmt);
// maybe add some handling for the case that closing failed.
}
}
row++;
}*/
std::cout << "Query " << _mSymbol << " ready" << std::endl;
}
database_con::~database_con() {
std::cout << "The database object has been deleted" << std::endl;
}
答案 0 :(得分：2)
&运算符来获取函数的地址。
std::thread t(&executeQuery, buildQuery(*_mVecHistIter, symbol));
^-- note the &
修改
所以，你忘记提到database_con是一个类。为了使用类成员函数作为函数接受指针的参数作为参数（在您的情况下为std::thread::thread），您必须使用带有操作数&（&database_con::executeQuery）的完全限定名称。但是，由于这是非静态成员函数，它将需要其第一个参数指针指向此类对象的实例（google std :: thread非静态成员函数）。
std::thread t(&database_con::executeQuery, this, buildQuery(*_mVecHistIter, symbol));
您是否考虑过使用std::function？
#include <functional>
#include <thread>
int foo(int arg1, int arg2)
{
return arg1 + arg2;
}
void bar(std::function<int(int, int)> fnc, int arg1, int arg2)
{
fnc(arg1, arg2);
}
int main()
{
std::thread thr{&bar, &foo, 1, 2};
}