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[英]Destructor to call free() to free dynamically allocated memory using malloc
[英]Not able to free memeory allocated by Malloc in
我有下面這段編寫的代碼,該代碼在調用時從內部數據庫中提取值。 數據庫第三列包含BLOB格式的值。 因此,對該數據庫的調用是提取開始時間和結束時間之間的所有列。 我正在使用malloc
unsigned char *valueBlobData = (unsigned char*)malloc(valueBlobSize);
為值bcoz保留內存一次可以有多個值。 現在,如果我使用:
free(valueBlobData)
列表historyRows
不包含任何值。 但是,如果我沒有空閑內存,那么我會在stl列表中收到值。 但這會導致內存泄漏。
問題是,我在錯誤的位置釋放了內存。 如果是,我如何使它工作?
bool SQHISDB::getHisVArray(unsigned long startTime, unsigned long endTime,
std::list<tHistoryRow> &historyRows)
{
int rc;
int counter = 0;
tHistoryRow tempHistoryRow; // Struct having four variables
unsigned int A1 =1, A2=2;
const char *zSql = "SELECT * "
"FROM node_values "
"WHERE A1 = ? "
"AND A2 = ? "
"AND (sourceTS BETWEEN ? AND ? ) "
";";
sqlite3_stmt *pStmt = NULL;
rc = sqlite3_prepare_v2(this->db, zSql, std::strlen(zSql), &pStmt, NULL);
if (rc != SQLITE_OK)
{
return rc;
}
sqlite3_bind_int(pStmt, 1, A1);
sqlite3_bind_int(pStmt, 2, A2);
sqlite3_bind_int64(pStmt, 3, startTime);
sqlite3_bind_int64(pStmt, 4, endTime;
while (sqlite3_step(pStmt) == SQLITE_ROW)
{
counter++;
unsigned long sourceTimestamp = sqlite3_column_int64(pStmt, 4);
unsigned int valueBlobSize = sqlite3_column_bytes(pStmt, 3);
unsigned char *valueBlobData = (unsigned char*)malloc(valueBlobSize);
std::memcpy(valueBlobData, sqlite3_column_blob(pStmt, SQLITE_HISTORYDB_INDEX_VALUE), valueBlobSize);
tempHistoryRow.sourceTimestamp = sourceTS;
tempHistoryRow.blobSize = valueBlobSize;
tempHistoryRow.blob = valueBlobData;
historyRows.push_back(tempHistoryRow);
free(valueBlobData);
}
sqlite3_finalize(pStmt);
return true;
}
實際上,您正在嘗試將historyRows
懸掛指針懸空。 這絕對是錯誤的。
對我來說,您似乎想使用簡單的向量來管理此緩沖區。
struct tHistoryRow {
std::vector<unsigned char> blob;
… … …
};
bool SQHISDB::getHisVArray(unsigned long startTime, unsigned long endTime,
std::list<tHistoryRow> &historyRows)
{
int rc;
int counter = 0;
unsigned int A1 =1, A2=2;
static const std::string zSql{ "SELECT * "
"FROM node_values "
"WHERE A1 = ? "
"AND A2 = ? "
"AND (sourceTS BETWEEN ? AND ? ) "
";" };
sqlite3_stmt *pStmt = NULL;
rc = sqlite3_prepare_v2(this->db, zSql.data(), zSql.length(), &pStmt, NULL);
if (rc != SQLITE_OK)
{
return rc;
}
sqlite3_bind_int(pStmt, 1, A1);
sqlite3_bind_int(pStmt, 2, A2);
sqlite3_bind_int64(pStmt, 3, startTime);
sqlite3_bind_int64(pStmt, 4, endTime;
while (sqlite3_step(pStmt) == SQLITE_ROW)
{
counter++;
unsigned long sourceTimestamp = sqlite3_column_int64(pStmt, 4);
unsigned int valueBlobSize = sqlite3_column_bytes(pStmt, 3);
tHistoryRow tempHistoryRow; // it would be nice to provide constructor
tempHistoryRow.blob.resize(valueBlobSize);
auto pBlob = sqlite3_column_blob(pStmt, SQLITE_HISTORYDB_INDEX_VALUE);
std::copy(pBlob, pBlob + valueBlobSize, tempHistoryRow.blob.begin());
tempHistoryRow.sourceTimestamp = sourceTS;
historyRows.push_back(std::move(tempHistoryRow));
}
sqlite3_finalize(pStmt);
return true;
}
釋放內存並不意味着“ 清除 ”內存,當您釋放內存時,它僅可用於其他分配,但是內存可能仍包含與調用free之前相同的內容( 或某些損壞的版本,這取決於方式)。分配器已實現 )。
嘗試檢查( 取消引用 )已傳遞給free()
的指針是未定義的行為。
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