[英]How do I call a custom free with QThreadStorage?
我在QThreadStorage中存儲的每個線程都有一個sqlite3 *實例。 問題是當我退出時,QThreadStorage刪除了指針。 我如何才能調用sqlite3_close呢?
您需要將sqlite3*
指針以及sqlite3_stmt*
包裝在RAII類中。 就像您應該使用C ++而不是C進行編程一樣,:)
此類確實存在,請參見此問題 ,例如,MIT許可的sqlite3pp項目。
一個沒有包裝所有API的非常簡單的實現,可以使用轉換運算符使該實例可與sqlite的C接口函數一起輕松使用。
// https://github.com/KubaO/stackoverflown/tree/master/questions/sqlite-threadstore-21536836
#include <QtCore>
#include <sqlite3.h>
class SQLiteStmt {
Q_DISABLE_COPY(SQLiteStmt)
sqlite3_stmt* m_stmt;
int m_rc;
friend class SQLiteDB;
private:
explicit SQLiteStmt(sqlite3_stmt* stmt, int rc) : m_stmt(stmt), m_rc(rc) {}
public:
SQLiteStmt(SQLiteStmt && o) : m_stmt(o.m_stmt), m_rc(o.m_rc) {
o.m_stmt = nullptr;
}
~SQLiteStmt() { sqlite3_finalize(m_stmt); m_stmt = nullptr; }
int status() const { return m_rc; }
operator sqlite3_stmt*() const { return m_stmt; }
};
class SQLiteDB {
Q_DISABLE_COPY(SQLiteDB)
sqlite3* m_db = nullptr;
public:
SQLiteDB() = default;
int open(const QString & filename) {
close();
return sqlite3_open16(filename.utf16(), &m_db);
}
int close() {
sqlite3* const db = m_db;
m_db = nullptr;
if (db) return sqlite3_close(db);
return SQLITE_OK;
}
int exec(const QString & sql) {
auto stmt = prepare(sql);
int rc = stmt.status();
if (rc == SQLITE_OK) do {
rc = sqlite3_step(stmt);
} while (rc == SQLITE_ROW);
return rc;
}
SQLiteStmt prepare(const QString & sql) {
sqlite3_stmt* stmt;
auto rc = sqlite3_prepare16_v2(m_db, sql.utf16(), -1, &stmt, nullptr);
return SQLiteStmt{stmt, rc};
}
~SQLiteDB() { close(); }
operator sqlite3*() const { return m_db; }
};
int main() {
QThreadStorage<SQLiteDB> dbData;
SQLiteDB & db(dbData.localData());
if (db.open(":memory:") != SQLITE_OK)
qDebug() << "open failed";
if (db.exec("CREATE TABLE myTable(value NUMERIC)") != SQLITE_DONE)
qDebug() << "create failed";
if (db.exec("INSERT INTO myTable VALUES (10), (20), (30)") != SQLITE_DONE)
qDebug() << "insert failed";
auto stmt = db.prepare("SELECT * FROM myTable");
if (stmt.status() == SQLITE_OK) while (true) {
int rc = sqlite3_step(stmt);
if (rc != SQLITE_ROW) break;
qDebug() << sqlite3_column_int(stmt, 0);
}
}
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